1.0 Definitions

1.1 “Active mode” means the condition during the heating season in which the vented heater is connected to the power source, and either the burner or any electrical auxiliary is activated.

1.2 “Air shutter” means an adjustable device for varying the size of the primary air inlet(s) to the combustion chamber power burner.

1.3 “Air tube” means a tube which carries combustion air from the burner fan to the burner nozzle for combustion.

1.4 “Barometic draft regulator or barometric damper” means a mechanical device designed to maintain a constant draft in a vented heater.

1.5   “Condensing vented heater” means a vented heater that, during the laboratory tests prescribed in this appendix, condenses part of the water vapor in the flue gases.

1.6 “Draft hood” means an external device which performs the same function as an integral draft diverter, as defined in section 1.17 of this appendix.

1.7 “Electro-mechanical stack damper” means a type of stack damper which is operated by electrical and/or mechanical means.

1.8 “Excess air” means air which passes through the combustion chamber and the vented heater flues in excess of that which is theoretically required for complete combustion.

1.9 “Flue” means a conduit between the flue outlet of a vented heater and the integral draft diverter, draft hood, barometric damper or vent terminal through which the flue gases pass prior to the point of draft relief.

1.10 “Flue damper” means a device installed between the furnace and the integral draft diverter, draft hood, barometric draft regulator, or vent terminal which is not equipped with a draft control device, designed to open the venting system when the appliance is in operation and to close the venting system when the appliance is in a standby condition.

1.11 “Flue gases” means reaction products resulting from the combustion of a fuel with the oxygen of the air, including the inerts and any excess air.

1.12 “Flue losses” means the sum of sensible and latent heat losses above room temperature of the flue gases leaving a vented heater.

1.13 “Flue outlet” means the opening provided in a vented heater for the exhaust of the flue gases from the combustion chamber.

1.14 “Heat input” (Qin) means the rate of energy supplied in a fuel to a vented heater operating under steady-state conditions, expressed in Btu's per hour. It includes any input energy to the pilot light and is obtained by multiplying the measured rate of fuel consumption by the measured higher heating value of the fuel.

1.15 “Heating capacity” (Qout) means the rate of useful heat output from a vented heater, operating under steady-state conditions, expressed in Btu's per hour. For room and wall heaters, it is obtained by multiplying the “heat input” (Qin) by the steady-state efficency (ηss) divided by 100. For floor furnaces, it is obtained by multiplying (A) the “heat input” (Qin) by (B) the steady-state efficiency divided by 100, minus the quantity (2.8) (Lj) divided by 100, where Lj is the jacket loss as determined in section 3.2 of this appendix.

1.16 “Higher heating value” (HHV) means the heat produced per unit of fuel when complete combustion takes place at constant pressure and the products of combustion are cooled to the initial temperature of the fuel and air and when the water vapor formed during combustion is condensed. The higher heating value is usually expressed in Btu's per pound, Btu's per cubic foot for gaseous fuel, or Btu's per gallon for liquid fuel.

1.17 “IEC 62301 (Second Edition)” means the test standard published by the International Electrotechnical Commission, titled “Household electrical appliances—Measurement of standby power,” Publication 62301 Edition 2.0 2011-01 (incorporated by reference; see §430.3).

1.18 “Induced draft” means a method of drawing air into the combustion chamber by mechanical means.

1.19 “Infiltration parameter” means that portion of unconditioned outside air drawn into the heated space as a consequence of loss of conditioned air through the exhaust system of a vented heater.

1.20 “Integral draft diverter” means a device which is an integral part of a vented heater, designed to: (1) Provide for the exhaust of the products of combustion in the event of no draft, back draft, or stoppage beyond the draft diverter, (2) prevent a back draft from entering the vented heater, and (3) neutralize the stack action of the chimney or gas vent upon the operation of the vented heater.

1.21 “Manually controlled vented heaters” means either gas or oil fueled vented heaters equipped without thermostats.

1.22 “Modulating control” means either a step-modulating or two-stage control.

1.23 “Off mode” means the condition during the non-heating season in which the vented heater is connected to the power source, and neither the burner nor any electrical auxiliary is activated.

1.24 “Power burner” means a vented heater burner which supplies air for combustion at a pressure exceeding atmospheric pressure, or a burner which depends on the draft induced by a fan incorporated in the furnace for proper operation.

1.25 “Reduced heat input rate” means the factory adjusted lowest reduced heat input rate for vented home heating equipment equipped with either two stage thermostats or step-modulating thermostats.

1.26 “Seasonal off switch” means the control device, such as a lever or toggle, on the vented heater that affects a difference in off mode energy consumption as compared to standby mode consumption.

1.27   “Single-stage thermostat” means a thermostat that cycles a burner at the maximum heat input rate and off.

1.28 “Stack” means the portion of the exhaust system downstream of the integral draft diverter, draft hood or barometric draft regulator.

1.29 “Stack damper” means a device installed downstream of the integral draft diverter, draft hood, or barometric draft regulator, designed to open the venting system when the appliance is in operation and to close off the venting system when the appliance is in the standby condition.

1.30 “Stack gases” means the flue gases combined with dilution air that enters at the integral draft diverter, draft hood or barometric draft regulator.

1.31 “Standby mode” means the condition during the heating season in which the vented heater is connected to the power source, and neither the burner nor any electrical auxiliary is activated.

1.32 “Steady-state conditions for vented home heating equipment” means equilibrium conditions as indicated by temperature variations of not more than 5 °F (2.8C) in the flue gas temperature for units equipped with draft hoods, barometric draft regulators or direct vent systems, in three successive readings taken 15 minutes apart or not more than 3 °F (1.7C) in the stack gas temperature for units equipped with integral draft diverters in three successive readings taken 15 minutes apart.

1.33 “Step-modulating control” means a control that either cycles off and on at the low input if the heating load is light, or gradually, increases the heat input to meet any higher heating load that cannot be met with the low firing rate.

1.34 “Thermal stack damper” means a type of stack damper which is dependent for operation exclusively upon the direct conversion of thermal energy of the stack gases into movement of the damper plate.

1.35 “Two stage control” means a control that either cycles a burner at the reduced heat input rate and off or cycles a burner at the maximum heat input rate and off.

1.36 “Vaporizing-type oil burner” means a device with an oil vaporizing bowl or other receptacle designed to operate by vaporizing liquid fuel oil by the heat of combustion and mixing the vaporized fuel with air.

1.37 “Vent/air intake terminal” means a device which is located on the outside of a building and is connected to a vented heater by a system of conduits. It is composed of an air intake terminal through which the air for combustion is taken from the outside atmosphere and a vent terminal from which flue gases are discharged.

1.38 “Vent limiter” means a device which limits the flow of air from the atmospheric diaphragm chamber of a gas pressure regulator to the atmosphere. A vent limiter may be a limiting orifice or other limiting device.

1.39 “Vent pipe” means the passages and conduits in a direct vent system through which gases pass from the combustion chamber to the outdoor air.

2.0 Testing conditions.

2.1 Installation of test unit.

2.1.1   Vented wall furnaces (including direct vent systems). Install non-direct vent gas fueled vented wall furnaces as specified in section 8.1.3 and figure 7 or figure 10 of ANSI Z21.86 (incorporated by reference, see §430.3). Install direct vent gas fueled vented wall furnaces as specified in section 6.1.3 and figure 6 of ANSI Z21.86 (incorporated by reference, see §430.3). Install oil fueled vented wall furnaces as specified in section 36.1 of UL 730 (incorporated by reference, see §430.3).

2.1.2   Vented floor furnaces. Install vented floor furnaces for test as specified in section 38.1 of UL 729 (incorporated by reference, see §430.3).

2.1.3   Vented room heaters. Install vented room heaters for test in accordance with the manufacturer's installation and operations (I&O) manual provided with the unit.

2.2 Flue and stack requirements.

2.2.1 Gas fueled vented home heating equipment employing integral draft diverters and draft hoods (excluding direct vent systems). Attach to, and vertically above the outlet of gas fueled vented home heating equipment employing draft diverters or draft hoods with vertically discharging outlets, a five (5) foot long test stack having a cross sectional area the same size as the draft diverter outlet.

Attach to the outlet of vented heaters having a horizontally discharging draft diverter or draft hood outlet a 90 degree elbow, and a five (5) foot long vertical test stack. A horizontal section of pipe may be used on the floor furnace between the diverter and the elbow if necessary to clear any framing used in the installation. Use the minimum length of pipe possible for this section. Use stack, elbow, and horizontal section with same cross sectional area as the diverter outlet.

2.2.2   Oil fueled vented home heating equipment (excluding direct vent systems). Use flue connections for oil fueled vented floor furnaces as specified in section 38.2 of UL 729, sections 36.2 of UL 730 for oil fueled vented wall furnaces, and sections 37.1.2 and 37.1.3 of UL 896 (all incorporated by reference, see §430.3) for oil fueled vented room heaters.

2.2.3 Direct vent systems. Have the exhaust/air intake system supplied by the manufacturer in place during all tests. Test units intended for installation with a variety of vent pipe lengths with the minimum length recommended by the manufacturer. Do not connect a heater employing a direct vent system to a chimney or induced draft source. Vent the gas solely on the provision for venting incorporated in the heater and the vent/air intake system supplied with it.

2.2.4   Condensing vented heater, additional flue requirements. The flue pipe installation must not allow condensate formed in the flue pipe to flow back into the unit. An initial downward slope from the unit's exit, an offset with a drip leg, annular collection rings, or drain holes must be included in the flue pipe installation without disturbing normal flue gas flow. Flue gases should not flow out of the drain with the condensate. For condensing vented heaters that do not include means for collection of condensate, a means to collect condensate must be supplied by the test lab for the purposes of testing.

2.3 Fuel supply.

2.3.1   Natural gas. For a gas fueled vented heater, maintain the gas supply to the unit under test at a normal inlet test pressure immediately ahead of all controls at 7 to 10 inches water column. Maintain the regulator outlet pressure at normal test pressure approximately at that recommended by the manufacturer. Use natural gas having a specific gravity of approximately 0.65 and a higher heating value within ±5 percent of 1,025 Btu's per standard cubic foot. Determine the actual higher heating value in Btu's per standard cubic foot for the natural gas to be used in the test with an error no greater than one percent.

2.3.2   Propane gas. For a propane-gas fueled vented heater, maintain the gas supply to the unit under test at a normal inlet pressure of 11 to 13 inches water column and a specific gravity of approximately 1.53. Maintain the regulator outlet pressure, on units so equipped, approximately at that recommended by the manufacturer. Use propane having a specific gravity of approximately 1.53 and a higher heating value within ±5 percent of 2,500 Btu's per standard cubic foot. Determine the actual higher heating value in Btu's per standard cubic foot for the propane to be used in the test

2.3.3   Other test gas. Use other test gases with characteristics as described in Table 4 of ANSI Z21.86 (incorporated by reference, see §430.3). Use gases with a measured higher heating value within ±5 percent of the values specified in the Tables section of ANSIZ21.86. Determine the actual higher heating value of the gas used in the test with an error no greater than one percent.

2.3.4   Oil supply. For an oil fueled vented heater, use No. 1 fuel oil (kerosene) for vaporizing-type burners and either No. 1 or No. 2 fuel oil, as specified by the manufacturer in the I&O manual provided with the unit, for mechanical atomizing type burners. Use test fuel conforming to the specifications given in Tables 2 and 3 of ASHRAE 103-2007 (incorporated by reference, see §430.3). Measure the higher heating value of the test fuel within ±1 percent.

2.3.5 Electrical supply. For auxiliary electric components of a vented heater, maintain the electrical supply to the test unit within one percent of the nameplate voltage for the entire test cycle. If a voltage range is used for nameplate voltage, maintain the electrical supply within one percent of the mid-point of the nameplate voltage range.

2.4 Burner adjustments.

2.4.1 Gas burner adjustments. Adjust the burners of gas fueled vented heaters to their maximum Btu ratings at the test pressure specified in section 2.3 of this appendix. Correct the burner volumetric flow rate to 60 °F (15.6C) and 30 inches of mercury barometric pressure, set the fuel flow rate to obtain a heat rate of within ±2 percent of the hourly Btu rating specified by the manufacturer as measured after 15 minutes of operation starting with all parts of the vented heater at room temperature. Set the primary air shutters in accordance with the manufacturer's recommendations to give a good flame at this adjustment. Do not allow the deposit of carbon during any test specified herein.

If a vent limiting means is provided on a gas pressure regulator, have it in place during all tests.

For gas fueled heaters with modulating controls adjust the controls to operate the heater at the maximum fuel input rate. Set the thermostat control to the maximum setting. Start the heater by turning the safety control valve to the “on” position. In order to prevent modulation of the burner at maximum input, place the thermostat sensing element in a temperature control bath which is held at a temperature below the maximum set point temperature of the control.

For gas fueled heaters with modulating controls adjust the controls to operate the heater at the reduced fuel input rate. Set the thermostat control to the minimum setting. Start the heater by turning the safety control valve to the “on” position. If ambient test room temperature is above the lowest control set point temperature, initiate burner operation by placing the thermostat sensing element in a temperature control bath that is held at a temperature below the minimum set point temperature of the control.

2.4.2   Oil burner adjustments. Adjust the burners of oil fueled vented heaters to give the CO2 reading recommended by the manufacturer and an hourly Btu input, during the steady-state performance test described below, which is within ±2 percent of the heater manufacturer's specified normal hourly Btu input rating. On units employing a power burner, do not allow smoke in the flue to exceed a No. 1 smoke during the steady-state performance test as measured by the procedure in ASTM D2156 (incorporated by reference, see §430.3). If, on units employing a power burner, the smoke in the flue exceeds a No. 1 smoke during the steady-state test, readjust the burner to give a lower smoke reading, and, if necessary a lower CO2 reading, and start all tests over. Maintain the average draft over the fire and in the flue during the steady-state performance test at that recommended by the manufacturer within ±0.005 inches of water gauge. Do not make additional adjustments to the burner during the required series of performance tests. The instruments and measuring apparatus for this test are described in section 6 and shown in Figure 8 of ASHRAE 103-2007 (incorporated by reference, see §430.3).

2.5 Circulating air adjustments.

2.5.1   Forced air vented wall furnaces (including direct vent systems). During testing, maintain the air flow through the heater as specified by the manufacturer in the I&O manual provided with the unit and operate the vented heater with the outlet air temperature between 80 °F and 130 °F above room temperature. If adjustable air discharge registers are provided, adjust them so as to provide the maximum possible air restriction. Measure air discharge temperature as specified in section 8.7 of ANSI Z21.86 (incorporated by reference, see §430.3).

2.5.2 Fan type vented room heaters and floor furnaces. During tests on fan type furnaces and heaters, adjust the air flow through the heater as specified by the manufacturer. If adjustable air discharge registers are provided, adjust them to provide the maximum possible air restriction.

2.6 Location of temperature measuring instrumentation.

2.6.1 Gas fueled vented home heating equipment (including direct vent systems). For units employing an integral draft diverter, install nine thermocouples, wired in parallel, in a horizontal plane in the five foot test stack located one foot from the test stack inlet. Equalize the length of all thermocouple leads before paralleling. Locate one thermocouple in the center of the stack. Locate eight thermocouples along imaginary lines intersecting at right angles in this horizontal plane at points one third and two thirds of the distance between the center of the stack and the stack wall.

For units which employ a direct vent system, locate at least one thermocouple at the center of each flue way exiting the heat exchanger. Provide radiation shields if the thermocouples are exposed to burner radiation.

For units which employ a draft hood or units which employ a direct vent system which does not significantly preheat the incoming combustion air, install nine thermocouples, wired in parallel, in a horizontal plane located within 12 inches (304.8 mm) of the heater outlet and upstream of the draft hood on units so equipped. Locate one thermocouple in the center of the pipe and eight thermocouples along imaginary lines intersecting at right angles in this horizontal plane at points one third and two thirds of the distance between the center of the pipe and the pipe wall.

For units which employ direct vent systems that significantly preheat the incoming combustion air, install nine thermocouples, wired in parallel, in a plane parallel to and located within 6 inches (152.4 mm) of the vent/air intake terminal. Equalize the length of all thermocouple leads before paralleling. Locate one thermocouple in the center of the vent pipe and eight thermocouples along imaginary lines intersecting at right angles in this plane at points one third and two thirds of the distance between the center of the flue pipe and the pipe wall.

Use bead-type thermocouples having wire size not greater than No. 24 American Wire Gauge (AWG). If there is a possibility that the thermocouples could receive direct radiation from the fire, install radiation shields on the fire side of the thermocouples only and position the shields so that they do not touch the thermocouple junctions.

Install thermocouples for measuring conditioned warm air temperature as described in Part VIII section 8.7 of ANSI Z21.86 (incorporated by reference, see §430.3). Establish the temperature of the inlet air by means of single No. 24 AWG bead-type thermocouple, suitably shielded from direct radiation and located in the center of the plane of each inlet air opening.

2.6.2 Oil fueled vented home heating equipment (including direct vent systems). Install nine thermocouples, wired in parallel and having equal length leads, in a plane perpendicular to the axis of the flue pipe. Locate this plane at the position shown in Figure 36.4 of UL 730, or Figure 38.1 and 38.2 of UL 729 (incorporated by reference, see §430.3) for a single thermocouple, except that on direct vent systems which significantly preheat the incoming combustion air, it shall be located within 6 inches (152.5 mm) of the outlet of the vent/air intake terminal. Locate one thermocouple in the center of the flue pipe and eight thermocouples along imaginary lines intersecting at right angles in this plane at points one third and two thirds of the distance between the center of the pipe and pipe wall.

Use bead-type thermocouples having a wire size not greater than No. 24 AWG. If there is a possibility that the thermocouples could receive direct radiation from the fire, install radiation shields on the fire side of the thermocouples only and position the shields so that they do not touch the thermocouple junctions.

Install thermocouples for measuring the conditioned warm air temperature as described in sections 37.5.8 through 37.5.18 of UL 730 (incorporated by reference, see §430.3). Establish the temperature of the inlet air by means of a single No. 24 AWG bead-type thermocouple, suitably shielded from direct radiation and located in the center of the plane of each inlet air opening.

2.7 Combustion measurement instrumentation. Analyze the samples of stack and flue gases for vented heaters to determine the concentration by volume of carbon dioxide present in the dry gas with instrumentation which will result in a reading having an accuracy of ±0.1 percentage points.

2.8 Energy flow instrumentation. Install one or more instruments, which measure the rate of gas flow or fuel oil supplied to the vented heater, and if appropriate, the electrical energy with an error no greater than one percent.

2.9   Room ambient temperature. The room ambient temperature shall be the arithmetic average temperature of the test area, determined by measurement with four No. 24 AWG bead-type thermocouples with junctions shielded against radiation, located approximately at 90-degree positions on a circle circumscribing the heater or heater enclosure under test, in a horizontal plane approximately at the vertical midpoint of the appliance or test enclosure, and with the junctions approximately 24 inches from sides of the heater or test enclosure and located so as not to be affected by other than room air.

The value TRA is the room ambient temperature measured at the last of the three successive readings taken 15 minutes apart described in section 3.1.1 or 3.1.2 as applicable. During the time period required to perform all the testing and measurement procedures specified in section 3.0 of this appendix, maintain the room ambient temperature within ±5 °F (±2.8 C) of the value TRA. At no time during these tests shall the room ambient temperature exceed 100 °F (37.8 C) or fall below 65 °F (18.3 C).

Locate a thermocouple at each elevation of draft relief inlet opening and combustion air inlet opening at a distance of approximately 24 inches from the inlet openings. The temperature of the air for combustion and the air for draft relief shall not differ more than ±5 °F from the room ambient temperature as measured above at any point in time. This requirement for combustion air inlet temperature does not need to be met once the burner is shut off during the testing described in sections 3.3 and 3.6 of this appendix.

2.10 Equipment used to measure mass flow rate in flue and stack. The tracer gas chosen for this task should have a density which is less than or approximately equal to the density of air. Use a gas unreactive with the environment to be encountered. Using instrumentation of either the batch or continuous type, measure the concentration of tracer gas with an error no greater than 2 percent of the value of the concentration measured.

2.11   Equipment with multiple control modes. For equipment that has both manual and automatic thermostat control modes, test the unit according to the procedure for its automatic control mode, i.e. single-stage, two stage, or step-modulating.

3.0 Testing and measurements.

3.1 Steady-state testing.

3.1.1   Gas fueled vented home heating equipment (including direct vent systems). Set up the vented heater as specified in sections 2.1, 2.2, and 2.3 of this appendix. The draft diverter shall be in the normal open condition and the stack shall not be insulated. (Insulation of the stack is no longer required for the vented heater test.) Begin the steady-state performance test by operating the burner and the circulating air blower, on units so equipped, with the adjustments specified by sections 2.4.1 and 2.5 of this appendix, until steady-state conditions are attained as indicated by three successive readings taken 15 minutes apart with a temperature variation of not more than ±3 °F (1.7 C) in the stack gas temperature for vented heaters equipped with draft diverters or ±5 °F (2.8 C) in the flue gas temperature for vented heaters equipped with either draft hoods or direct vent systems. The measurements described in this section are to coincide with the last of these 15 minute readings.

On units employing draft diverters, measure the room temperature (TRA) as described in section 2.9 of this appendix and measure the steady-state stack gas temperature (TS,SS) using the nine thermocouples located in the 5 foot test stack as specified in section 2.6.1 of this appendix. Secure a sample of the stack gases in the plane where TS,SS is measured or within 3.5 feet downstream of this plane. Determine the concentration by volume of carbon dioxide (XCO2S) present in the dry stack gas. If the location of the gas sampling differs from the temperature measurement plane, there shall be no air leaks through the stack between these two locations.

On units employing draft hoods or direct vent systems, measure the room temperature (TRA) as described in section 2.9 of this appendix and measure the steady-state flue gas temperature (TF,SS), using the nine thermocouples located in the flue pipe as described in section 2.6.1 of this appendix. Secure a sample of the flue gas in the plane of temperature measurement and determine the concentration by volume of CO2 (XCO2F) present in dry flue gas. In addition, for units employing draft hoods, secure a sample of the stack gas in a horizontal plane in the five foot test stack located one foot from the test stack inlet; and determine the concentration by volume of CO2 (XCO2S) present in dry stack gas.

Determine the steady-state heat input rate (Qin) including pilot gas by multiplying the measured higher heating value of the test gas by the steady-state gas input rate corrected to standard conditions of 60 °F and 30 inches of mercury. Use measured values of gas temperature and pressure at the meter and the barometric pressure to correct the metered gas flow rate to standard conditions.

After the above test measurements have been completed on units employing draft diverters, secure a sample of the flue gases at the exit of the heat exchanger(s) and determine the concentration of CO2 (XCO2F) present. In obtaining this sample of flue gas, move the sampling probe around or use a sample probe with multiple sampling ports in order to assure that an average value is obtained for the CO2 concentration. For units with multiple heat exchanger outlets, measure the CO2 concentration in a sample from each outlet to obtain the average CO2 concentration for the unit. A manifold (parallel connected sampling tubes) may be used to obtain this sample.

For heaters with single-stage thermostat control (wall mounted electric thermostats), determine the steady-state efficiency at the maximum fuel input rate as specified in section 2.4 of this appendix.

For gas fueled vented heaters equipped with either two stage control or step-modulating control, determine the steady-state efficiency at the maximum fuel input rate and at the reduced fuel input rate, as specified in section 2.4.1 of this appendix.

For manually controlled gas fueled vented heaters with various input rates, determine the steady-state efficiency at a fuel input rate that is within ±5 percent of 50 percent of the maximum rated fuel input rate as indicated on the nameplate of the unit or in the manufacturer's installation and operation manual shipped with the unit. If the heater is designed to use a control that precludes operation at other than maximum rated fuel input rate (single firing rate) determine the steady state efficiency at the maximum rated fuel input rate only.

3.1.2   Oil fueled vented home heating equipment (including direct vent systems). Set up and adjust the vented heater as specified in sections 2.1, 2.2, and 2.3.4 of this appendix. Begin the steady-state performance test by operating the burner and the circulating air blower, on units so equipped, with the adjustments specified by sections 2.4.2 and 2.5 of this appendix, until steady-state conditions are attained as indicated by a temperature variation of not more than ±5 °F (2.8 C) in the flue gas temperature in three successive readings taken 15 minutes apart. The measurements described in this section are to coincide with the last of these 15 minutes readings.

For units equipped with power burners, do not allow smoke in the flue to exceed a No. 1 smoke during the steady-state performance test as measured by the procedure described in ASTM D2156 (incorporated by reference, see §430.3). Maintain the average draft over the fire and in the breeching during the steady-state performance test at that recommended by the manufacturer ±0.005 inches of water gauge.

Measure the room temperature (TRA) as described in section 2.9 of this appendix. Measure the steady-state flue gas temperature (TF,SS) using nine thermocouples located in the flue pipe as described in section 2.6.2 of this appendix. From the plane where TF,SS was measured, collect a sample of the flue gas and determine the concentration by volume of CO2 (XCO2F) present in dry flue gas. Measure and record the steady-state heat input rate (Qin).

For manually controlled oil fueled vented heaters, determine the steady-state efficiency at a fuel input rate that is within ±5 percent of 50 percent of the maximum fuel input rate; or, if the design of the heater is such that the fuel input rate cannot be set to ±5 percent of 50 percent of the maximum rated fuel input rate, determine the steady-state efficiency at the minimum rated fuel input rate as measured in section 3.1.2 of this appendix for manually controlled oil fueled vented heaters.

3.1.3 Auxiliary Electric Power Measurement. Allow the auxiliary electrical system of a gas or oil vented heater to operate for at least five minutes before recording the maximum auxiliary electric power measurement from the wattmeter. Record the maximum electric power (PE) expressed in kilowatts. For vented heaters with modulating controls, the recorded (PE) shall be maximum measured electric power multiplied by the following factor (R). For two stage controls, R = 1.3. For step modulating controls, R = 1.4 when the ratio of minimum-to-maximum fuel input is greater than or equal to 0.7, R = 1.7 when the ratio of minimum-to-maximum fuel input is less than 0.7 and greater than or equal to 0.5, and R = 2.2 when the ratio of minimum-to-maximum fuel input is less than 0.5.

3.2   Jacket loss measurement. Conduct a jacket loss test for vented floor furnaces. Measure the jacket loss (Lj) in accordance with ASHRAE 103-2007 section 8.6 (incorporated by reference, see §430.3), applying the provisions for furnaces and not the provisions for boilers.

3.3   Measurement of the off-cycle losses for vented heaters equipped with thermal stack dampers. Unless specified otherwise, the thermal stack damper should be at the draft diverter exit collar. Attach a five foot length of bare stack to the outlet of the damper. Install thermocouples as specified in section 2.6.1 of this appendix.

For vented heaters equipped with single-stage thermostats, measure the off-cycle losses at the maximum fuel input rate. For vented heaters equipped with two stage thermostats, measure the off-cycle losses at the maximum fuel input rate and at the reduced fuel input rate. For vented heaters equipped with step-modulating thermostats, measure the off-cycle losses at the reduced fuel input rate.

Allow the vented heater to heat up to a steady-state condition. Feed a tracer gas at a constant metered rate into the stack directly above and within one foot above the stack damper. Record tracer gas flow rate and temperature. Measure the tracer gas concentration in the stack at several locations in a horizontal plane through a cross-section of the stack at a point sufficiently above the stack damper to ensure that the tracer gas is well mixed in the stack.

Continuously measure the tracer gas concentration and temperature during a 10-minute cool-down period. Shut the burner off and immediately begin measuring tracer gas concentration in the stack, stack temperature, room temperature, and barometric pressure. Record these values as the midpoint of each one-minute interval between burner shut-down and ten minutes after burner shut-down. Meter response time and sampling delay time shall be considered in timing these measurements.

3.4 Measurement of the effectiveness of electro-mechanical stack dampers. For vented heaters equipped with electro-mechanical stack dampers, measure the cross sectional area of the stack (As), the net area of the damper plate (Ao), and the angle that the damper plate makes when closed with a plane perpendicular to the axis of the stack (Ω). The net area of the damper plate means the area of the damper plate minus the area of any holes through the damper plate.

3.5 Pilot light measurement.

3.5.1 Measure the energy input rate to the pilot light (QP) with an error no greater than 3 percent for vented heaters so equipped.

3.5.2 For manually controlled heaters where the pilot light is designed to be turned off by the user when the heater is not in use, that is, turning the control to the OFF position will shut off the gas supply to the burner(s) and to the pilot light, the measurement of QP is not needed. This provision applies only if an instruction to turn off the unit is provided on the heater near the gas control valve (e.g. by label) by the manufacturer.

3.6 Optional procedure for determining Dp′ DF′ and Ds for systems for all types of vented heaters. For all types of vented heaters, Dp′ DF′ and DS can be measured by the following optional cool down test.

Conduct a cool down test by letting the unit heat up until steady-state conditions are reached, as indicated by temperature variation of not more than 5 °F (2.8 °C) in the flue gas temperature in three successive readings taken 15 minutes apart, and then shutting the unit off with the stack or flue damper controls by-passed or adjusted so that the stack or flue damper remains open during the resulting cool down period. If a draft was maintained on oil fueled units in the flue pipe during the steady-state performance test described in section 3.1 of this appendix, maintain the same draft (within a range of −.001 to + .005 inches of water gauge of the average steady-state draft) during this cool down period.

Measure the flue gas mass flow rate (mF,OFF) during the cool down test described above at a specific off-period flue gas temperature and corrected to obtain its value at the steady-state flue gas temperature (TF,SS), using the procedure described below.

Within one minute after the unit is shut off to start the cool down test for determining DF, begin feeding a tracer gas into the combustion chamber at a constant flow rate of VT, and at a point which will allow for the best possible mixing with the air flowing through the chamber. (On units equipped with an oil fired power burner, the best location for injecting this tracer gas appears to be through a hole drilled in the air tube.) Periodically measure the value of VT with an instantaneously reading flow meter having an accuracy of ±3 percent of the quantity measured. Maintain VT at less than 1 percent of the air flow rate through the furnace. If a combustible tracer gas is used, there should be a delay period between the time the burner gas is shut off and the time the tracer gas is first injected to prevent ignition of the tracer gas.

Between 5 and 6 minutes after the unit is shut off to start the cool down test, measure at the exit of the heat exchanger the average flue gas temperature, T*F,Off. At the same instant the flue gas temperature is measured, also measure the percent volumetric concentration of tracer gas CT in the flue gas in the same plane where T*F,Off is determined. Obtain the concentration of tracer gas using an instrument which will result in an accuracy of ±2 percent in the value of CT measured. If use of a continuous reading type instrument results in a delay time between drawing of a sample and its analysis, this delay should be taken into account so that the temperature measurement and the measurement of tracer gas concentration coincide. In addition, determine the temperature of the tracer gas entering the flow meter (TT) and the barometric pressure (PB).

The rate of the flue gas mass flow through the vented heater and the factors DP, DF, and DS are calculated by the equations in sections 4.5.1 through 4.5.3 of this appendix.

3.6.1   Procedure for determining (DF and DP) of vented home heating equipment with no measurable airflow. On units whose design is such that there is no measurable airflow through the combustion chamber and heat exchanger when the burner(s) is off (as determined by the test procedure in section 3.6.2 of this appendix), DF and DP may be set equal to 0.05.

3.6.2   Test Method to Determine Whether the Use of the Default Draft Factors (DF and DP) of 0.05 is Allowed. Manufacturers may use the following test protocol to determine whether air flows through the combustion chamber and heat exchanger when the burner(s) is off using a smoke stick device. The default draft factor of 0.05 (as allowed per section 3.6.1 of this appendix) may be used only for units determined pursuant to this protocol to have no air flow through the combustion chamber and heat exchanger.

3.6.2.1   Test Conditions. Wait for two minutes following the termination of the vented heater's on-cycle.

3.6.2.2   Location of Test Apparatus

3.6.2.2.1   After all air currents and drafts in the test chamber have been minimized, position the operable smoke stick/pencil as specified, based on the following equipment configuration: for horizontal combustion air intakes, approximately 4 inches from the vertical plane at the termination of the intake vent and 4 inches below the bottom edge of the combustion air intake, or for vertical combustion air intakes, approximately 4 inches horizontal from vent perimeter at the termination of the intake vent and 4 inches down (parallel to the vertical axis of the vent). In the instance where the boiler combustion air intake is closer than 4 inches to the floor, place the smoke device directly on the floor without impeding the flow of smoke.

3.6.2.2.2   Monitor the presence and the direction of the smoke flow.

3.6.2.3   Duration of Test. Continue monitoring the release of smoke for no less than 30 seconds.

3.6.2.4   Test Results

3.6.2.4.1   During visual assessment, determine whether there is any draw of smoke into the combustion air intake.

3.6.2.4.2   If absolutely no smoke is drawn into the combustion air intake, the vented heater meets the requirements to allow use of the default draft factor of 0.05 pursuant to Section 8.8.3 and/or 9.10 of ASHRAE 103-2007 (incorporated by reference, see §430.3).

3.6.2.4.3   If there is any smoke drawn into the intake, use of default draft factor of 0.05 is prohibited. Proceed with the methods of testing as prescribed in section 3.6 of this appendix, or select the appropriate default draft factor from Table 1.

3.7 Measurement of electrical standby mode and off mode power.

3.7.1 Standby power measurements. With all electrical auxiliaries of the vented heater not activated, measure the standby power (PW,SB) in accordance with the procedures in IEC 62301 (Second Edition) (incorporated by reference, see §430.3), except that section 2.9, Room ambient temperature, and the voltage provision of section 2.3.5, Electrical supply, of this appendix shall apply in lieu of the IEC 62301 (Second Edition) corresponding sections 4.2, Test room, and 4.3, Power supply. Clarifying further, the IEC 62301 (Second Edition) sections 4.4, Power measuring instruments, and section 5, Measurements, shall apply in lieu of section 2.8, Energy flow instrumentation, of this appendix. Measure the wattage so that all possible standby mode wattage for the entire appliance is recorded, not just the standby mode wattage of a single auxiliary. The recorded standby power (PW,SB) shall be rounded to the second decimal place, and for loads greater than or equal to 10W, at least three significant figures shall be reported.

3.7.2 Off mode power measurement. If the unit is equipped with a seasonal off switch or there is an expected difference between off mode power and standby mode power, measure off mode power (PW,OFF) in accordance with the standby power procedures in IEC 62301 (Second Edition) (incorporated by reference, see §430.3), except that section 2.9, Room ambient temperature, and the voltage provision of section 2.3.5, Electrical supply, of this appendix shall apply in lieu of the IEC 62301 (Second Edition) corresponding sections 4.2, Test room, and 4.3, Power supply. Clarifying further, the IEC 62301 (Second Edition) sections 4.4, Power measuring instruments, and section 5, Measurements, shall apply in lieu of section 2.8, Energy flow instrumentation, of this appendix. Measure the wattage so that all possible off mode wattage for the entire appliance is recorded, not just the off mode wattage of a single auxiliary. If there is no expected difference in off mode power and standby mode power, let PW,OFF = PW,SB, in which case no separate measurement of off mode power is necessary. The recorded off mode power (PW,OFF) shall be rounded to the second decimal place, and for loads greater than or equal to 10W, at least three significant figures shall be reported.

3.8   Condensing vented heaters—measurement of condensate under steady-state and cyclic conditions. Attach condensate drain lines to the vented heater as specified in the manufacturer's I&O manual provided with the unit. The test unit shall be level prior to all testing. A continuous downward slope of drain lines from the unit shall be maintained. The drain lines must facilitate uninterrupted flow of condensate during the test. The condensate collection container must be glass or polished stainless steel to facilitate removal of interior deposits. The collection container shall have a vent opening to the atmosphere, be dried prior to each use, and be at room ambient temperature. The humidity of the room air shall at no time exceed 80 percent relative humidity. For condensing units not designed for collecting and draining condensate, drain lines must be provided during testing that meet the criteria set forth in this section 3.8. Units employing manual controls and units not tested under the optional tracer gas procedures of sections 3.3 and 3.6 of this appendix shall only conduct the steady-state condensate collection test.

3.8.1   Steady-state condensate collection test. Begin steady-state condensate collection concurrently with or immediately after completion of the steady-state testing of section 3.1 of this appendix. The steady-state condensate collection period shall be 30 minutes. Condensate mass shall be measured immediately at the end of the collection period to minimize evaporation loss from the sample. Record fuel input during the 30-minute condensate collection steady-state test period. Measure and record fuel higher heating value (HHV), temperature, and pressures necessary for determining fuel energy input (Qc,ss). The fuel quantity and HHV shall be measured with errors no greater than ±1 percent. Determine the mass of condensate for the steady-state test (Mc,ss) in pounds by subtracting the tare container weight from the total container and condensate weight measured at the end of the 30-minute condensate collection test period. The error associated with the mass measurement instruments shall not exceed ±0.5 percent of the quantity measured.

For units with step-modulating or two stage controls, the steady-state condensate collection test shall be conducted at both the maximum and reduced input rates.

3.8.2   Cyclic condensate collection tests. If existing controls do not allow for cyclical operation of the tested unit, control devices shall be installed to allow cyclical operation of the vented heater. Run three consecutive test cycles. For each cycle, operate the unit until flue gas temperatures at the end of each on-cycle, rounded to the nearest whole number, are within 5 °F of each other for two consecutive cycles. On-cycle and off-cycle times are 4 minutes and 13 minutes respectively. Control of ON and OFF operation actions shall be within ±6 seconds of the scheduled time. For fan-type vented heaters, maintain circulating air adjustments as specified in section 2.5 of this appendix. Begin condensate collection at one minute before the on-cycle period of the first test cycle. Remove the container one minute before the end of each off-cycle period. Measure condensate mass for each test-cycle. The error associated with the mass measurement instruments shall not exceed ±0.5 percent of the quantity measured.

Fuel input shall be recorded during the entire test period starting at the beginning of the on-time period of the first cycle to the beginning of the on-time period of the second cycle, from the beginning of the on-time period of the second cycle to the beginning of the on-time period of the third cycle, etc., for each of the test cycles. Fuel HHV, temperature, and pressure necessary for determining fuel energy input, Qc, shall be recorded. Determine the mass of condensate for each cycle, Mc, in pounds. If at the end of three cycles, the sample standard deviation is within 20 percent of the mean value for three cycles, use total condensate collected in the three cycles as Mc; if not, continue collection for an additional three cycles and use the total condensate collected for the six cycles as Mc. Determine the fuel energy input, Qc, during the three or six test cycles, expressed in Btu.

4.0 Calculations.

4.1   Annual fuel utilization efficiency for gas fueled or oil fueled vented home heating equipment equipped without manual controls or with multiple control modes as per 2.11 and without thermal stack dampers. The following procedure determines the annual fuel utilization efficiency for gas fueled or oil fueled vented home heating equipment equipped without manual controls and without thermal stack dampers.

4.1.1 System number. Obtain the system number from Table 1 of this appendix.

4.1.2   Off-cycle flue gas draft factor. Based on the system number, determine the off-cycle flue gas draft factor (DF) from Table 1 of this appendix or the test method and calculations of sections 3.6 and 4.5 of this appendix.

4.1.3   Off-cycle stack gas draft factor. Based on the system number, determine the off-cycle stack gas draft factor (Ds) from Table 1 of this appendix or from the test method and calculations of sections 3.6 and 4.5 of this appendix,.

4.1.4 Pilot fraction. Calculate the pilot fraction (PF) expressed as a decimal and defined as:

PF = QP/Qin

where:

QP = as defined in 3.5 of this appendix

Qin = as defined in 3.1 of this appendix at the maximum fuel input rate

4.1.5 Jacket loss for floor furnaces. Determine the jacket loss (Lj) expressed as a percent and measured in accordance with section 3.2 of this appendix. For other vented heaters Lj = 0.0.

4.1.6   Latent heat loss. For non-condensing vented heaters, obtain the latent heat loss (LL,A) from Table 2 of this appendix. For condensing vented heaters, calculate a modified latent heat loss (LL,A*) as follows:

For steady-state conditions:

LL,A*= LL,A−LG,SS + LC,SS

where:

LL,A = Latent heat loss, based on fuel type, from Table 2 of this appendix,

LG,SS = Steady-state latent heat gain due to condensation as determined in section 4.1.6.1 of this appendix, and

LC,SS = Steady-state heat loss due to hot condensate going down the drain as determined in 4.1.6.2 of this appendix.

For cyclic conditions: (only for vented heaters tested under the optional tracer gas procedures of section 3.3 or 3.6)

LL,A*= LL,A−LG + LC

where:

LL,A = Latent heat loss, based on fuel type, from Table 2 of this appendix,

LG = Latent heat gain due to condensation under cyclic conditions as determined in section 4.1.6.3 of this appendix, and

LC = Heat loss due to hot condensate going down the drain under cyclic conditions as determined in section 4.1.6.4 of this appendix.

4.1.6.1   Latent heat gain due to condensation under steady-state conditions. Calculate the latent heat gain (LG,SS) expressed as a percent and defined as:

where:

100 = conversion factor to express a decimal as a percent,

1053.3 = latent heat of vaporization of water, Btu per pound,

Mc,ss = mass of condensate for the steady-state test as determined in section 3.8.1 of this appendix, pounds, and

Qc,ss = fuel energy input for steady-state test as determined in section 3.8.1 of this appendix, Btu.

4.1.6.2   Heat loss due to hot condensate going down the drain under steady-state conditions. Calculate the steady-state heat loss due to hot condensate going down the drain (LC,SS) expressed as a percent and defined as:

where:

LG,SS = Latent heat gain due to condensation under steady-state conditions as defined in section 4.1.6.1 of this appendix,

1.0 = specific heat of water, Btu/lb− °F,

TF,SS = Flue (or stack) gas temperature as defined in section 3.1 of this appendix, °F,

70 = assumed indoor temperature, °F,

0.45 = specific heat of water vapor, Btu/lb− °F, and

45 = average outdoor temperature for vented heaters, °F.

4.1.6.3   Latent heat gain due to condensation under cyclic conditions. (only for vented heaters tested under the optional tracer gas procedures of section 3.3 or 3.6 of this appendix) Calculate the latent heat gain (LG) expressed as a percent and defined as:

where:

100 = conversion factor to express a decimal as a percent,

1053.3 = latent heat of vaporization of water, Btu per pound,

Mc = mass of condensate for the cyclic test as determined in 3.8.2 of this appendix, pounds, and

Qc = fuel energy input for cyclic test as determined in 3.8.2 of this appendix, Btu.

4.1.6.4   Heat loss due to hot condensate going down the drain under cyclic conditions. (only for vented heaters tested under the optional tracer gas procedures of section 3.3 or 3.6 of this appendix) Calculate the cyclic heat loss due to hot condensate going down the drain (LC) expressed as a percent and defined as:

where:

LG = Latent heat gain due to condensation under cyclic conditions as defined in section 4.1.6.3 of this appendix,

1.0 = specific heat of water, Btu/lb− °F,

TF,SS = Flue (or stack) gas temperature as defined in section 3.1 of this appendix,

70 = assumed indoor temperature, °F,

0.45 = specific heat of water vapor, Btu/lb− °F, and

45 = average outdoor temperature for vented heaters, °F.

4.1.7 Ratio of combustion air mass flow rate to stoichiometric air mass flow rate. Determine the ratio of combustion air mass flow rate to stoichiometric air mass flow rate (RT,F), and defined as:

RT,F = A + B/XCO2F

where:

A = as determined from Table 2 of this appendix

B = as determined from Table 2 of this appendix

XCO2F = as defined in 3.1 of this appendix

4.1.8   Ratio of combustion and relief air mass flow rate to stoichiometric air mass flow rate. For vented heaters equipped with either an integral draft diverter or a draft hood, determine the ratio of combustion and relief air mass flow rate to stoichiometric air mass flow rate (RT,S), and defined as:

RT,S = A + [B/XCO2S]

where:

A = as determined from Table 2 of this appendix,

B = as determined from Table 2 of this appendix, and

XCO2S = as defined in section 3.1 of this appendix.

4.1.9 Sensible heat loss at steady-state operation. For vented heaters equipped with either an integral draft diverter or a draft hood, determine the sensible heat loss at steady-state operation (LS,SS,A) expressed as a percent and defined as:

where:

LS,SS,A = C(RT,S + D)(TS,SS−TRA)

C = as determined from Table 2 of this appendix

RT,S = as defined in 4.1.8 of this appendix

D = as determined from Table 2 of this appendix

TS,SS = as defined in 3.1 of this appendix

TRA = as defined in 2.9 of this appendix

For vented heaters equipped without an integral draft diverter, determine (LS,SS,A) expressed as a percent and defined as:

LS,SS,A = C(RT,F + D)(TF,SS−TRA)

where:

C = as determined from Table 2 of this appendix

RT,F = as defined in 4.1.7 of this appendix

D = as determined from Table 2 of this appendix

TF,SS = as defined in 3.1 of this appendix

TRA = as defined in 2.9 of this appendix

4.1.10   Steady-state efficiency. For vented heaters equipped with single-stage thermostats, calculate the steady-state efficiency (excluding jacket loss), ηSS, expressed in percent and defined as:

ηSS = 100−LL,A−LS,SS,A

where:

LL,A = latent heat loss, as defined in section 4.1.6 of this appendix (for condensing vented heaters LL,A* for steady-state conditions), and

LS,SS,A = sensible heat loss at steady-state operation, as defined in section 4.1.9 of this appendix.

For vented heaters equipped with either two stage controls or with step-modulating controls, calculate the steady-state efficiency at the reduced fuel input rate, ηSS−L, expressed in percent and defined as:

ηSS−L = 100−LL,A−LS,SS,A

where:

LL,A = latent heat loss, as defined in section 4.1.6 of this appendix (for condensing vented heaters LL,A* for steady-state conditions at the reduced firing rate), and

LS,SS,A = sensible heat loss at steady-state operation, as defined in section 4.1.9 of this appendix, in which LS,SS,A is determined at the reduced fuel input rate.

For vented heaters equipped with two stage controls, calculate the steady-state efficiency at the maximum fuel input rate, ηSS−H, expressed in percent and defined as:

ηSS−H = 100−LL,A−LS,SS,A

where:

LL,A = latent heat loss, as defined in section 4.1.6 of this appendix (for condensing vented heaters LL,A* for steady-state conditions at the maximum fuel input rate), and

LS,SS,A = sensible heat loss at steady-state operation, as defined in section 4.1.9 of this appendix, in which LS,SS,A is measured at the maximum fuel input rate.

For vented heaters equipped with step-modulating thermostats, calculate the weighted-average steady-state efficiency in the modulating mode, ηSS−MOD, expressed in percent and defined as:

where:

ηSS-H = steady-state efficiency at the maximum fuel input rate, as defined in section 4.1.10 of this appendix,

ηSS-L = steady-state efficiency at the reduced fuel input rate, as defined in section 4.1.10 of this appendix,

TOA* = average outdoor temperature for vented heaters with step-modulating thermostats operating in the modulating mode and is obtained from Table 3 or Figure 1 of this appendix, and

TC = balance point temperature which represents a temperature used to apportion the annual heating load between the reduced input cycling mode and either the modulating mode or maximum input cycling mode and is obtained either from Table 3 of this appendix or calculated by the following equation:

TC = 65−[(65−15)R]

where:

65 = average outdoor temperature at which a vented heater starts operating,

15 = national average outdoor design temperature for vented heaters, and

R = ratio of reduced to maximum heat output rates, as defined in section 4.1.13 of this appendix.

4.1.11 Reduced heat output rate. For vented heaters equipped with either two stage thermostats or step-modulating thermostats, calculate the reduced heat output rate

(Qred-out) defined as:

Qred-out = ηSS-L Qred-in

where:

ηSS-L = as defined in 4.1.10 of this appendix

Qred-in = the reduced fuel input rate

4.1.12 Maximum heat output rate. For vented heaters equipped with either two stage thermostats or step-modulating thermostas, calculate the maximum heat output rate (Qmax-out) defined as:

Qmax,out = hSS,H Qmax,in

where:

ηSS-H = as defined in 4.1.10 of this appendix

Qmax-in = the maximum fuel input rate

4.1.13 Ratio of reduced to maximum heat output rates. For vented heaters equipped with either two stage thermostats or step-modulating thermostats, calculate the ratio of reduced to maximum heat output rates (R) expressed as a decimal and defined as:

R = Qred-out/Qmax-out

where:

Qred-out = as defined in 4.1.11 of this appendix

Qmax-out = as defined in 4.1.12 of this appendix

4.1.14 Fraction of heating load at reduced operating mode. For vented heaters equipped with either two stage thermostats or step-modulating thermostats, determine the fraction of heating load at the reduced operating mode (X1) expressed as a decimal and listed in Table 3 of this appendix or obtained from Figure 2 of this appendix.

4.1.15   Fraction of heating load at maximum operating mode or noncycling mode. For vented heaters equipped with either two stage thermostats or step-modulating thermostats, determine the fraction of heating load at the maximum operating mode or noncycling mode (X2) expressed as a decimal and listed in Table 3 of this appendix or obtained from Figure 2 of this appendix.

4.1.16   Weighted-average steady-state efficiency. For vented heaters equipped with single-stage thermostats, the weighted-average steady-state efficiency (ηSS-WT) is equal to ηSS, as defined in section 4.1.10 of this appendix. For vented heaters equipped with two stage thermostats, ηSS-WT is defined as:

ηSS-WT = X1ηSS-L + X2ηSS-H

where:

X1 = as defined in section 4.1.14 of this appendix

ηSS-L = as defined in section 4.1.10 of this appendix

X2 = as defined in section 4.1.15 of this appendix

ηSS-H = as defined in section 4.1.10 of this appendix

For vented heaters equipped with step-modulating controls, ηSS-WT is defined as:

ηSS-WT = X1ηSS-L + X2ηSS-MOD

where:

X1 = as defined in section 4.1.14 of this appendix

ηSS-L = as defined in section 4.1.10 of this appendix

X2 = as defined in section 4.1.15 of this appendix

ηSS-MOD = as defined in section 4.1.10 of this appendix

4.1.17 Annual fuel utilization efficiency. Calculate the annual fuel utilization efficiency (AFUE) expressed as percent and defined as:

AFUE=[0.968ηSS − WT] − 1.78DF − 1.89DS − 129PF − 2.8 LJ + 1.81

where:

ηSS-WT = as defined in 4.1.16 of this appendix

DF = as defined in 4.1.2 of this appendix

DS = as defined in 4.1.3 of this appendix

PF = as defined in 4.1.4 of this appendix

LJ = as defined in 4.1.5 of this appendix

4.2 Annual fuel utilization efficiency for gas or oil fueled vented home heating equipment equipped with manual controls. The following procedure determines the annual fuel utilization efficiency for gas or oil fueled vented home heating equipment equipped with manual controls.

4.2.1   Average ratio of stack gas mass flow rate to flue gas mass flow rate at steady-state operation. For vented heaters equipped with either direct vents or direct exhaust or that are outdoor units, the average ratio of stack gas mass flow rate to flue gas mass flow rate at steady-state operation (S/F) shall be equal to unity. (S/F = 1) For all other types of vented heaters, calculate (S/F) defined as:

where:

RT,S = as defined in section 4.1.8 of this appendix with XCO2s as measured in section 3.1. of this appendix

RT,F = as defined in section 4.1.7 of this appendix with XCO2F as measured in section 3.1. of this appendix

4.2.2   Multiplication factor for infiltration loss during burner on-cycle. Calculate the multiplication factor for infiltration loss during burner on-cycle (KI,ON) defined as:

where:

100 = converts a decimal fraction into a percent

0.24 = specific heat of air

A/F = stoichiometric air/fuel ratio, determined in accordance with Table 2 of this appendix

S/F = as defined in section 4.2.1 of this appendix

0.7 = infiltration parameter

RT,F = as defined in section 4.1.7 of this appendix

HHVA = average higher heating value of the test fuel, determined in accordance with Table 2 of this appendix

4.2.3 On-cycle infiltration heat loss. Calculate the on-cycle infiltration heat loss (LI,ON) expressed as a percent and defined as:

LI,ON = KI,ON (70-45)

where:

KI,ON = as defined in 4.2.2 of this appendix

70 = average indoor temperature

45 = average outdoor temperature

4.2.4 Weighted-average steady-state efficiency.

4.2.4.1   For manually controlled heaters with various input rates the weighted average steady-state efficiency (ηSS−WT), is determined as follows:

ηSS-WT = 100−LL,A−LS,SS,A

where:

LL,A = latent heat loss, as defined in section 4.1.6 of this appendix (for condensing vented heaters, LL,A* for steady-state conditions), and

LS,SS,A = steady-state efficiency at the reduced fuel input rate, as defined in section 4.1.9 of this appendix and where LL,A and LS,SS,A are determined:

(1) at 50 percent of the maximum fuel input rate as measured in either section 3.1.1 of this appendix for manually controlled gas vented heaters or section 3.1.2 of this appendix for manually controlled oil vented heaters, or

(2) at the minimum fuel input rate as measured in either section 3.1.1 of this appendix for manually controlled gas vented heaters or section 3.1.2 of this appendix for manually controlled oil vented heaters if the design of the heater is such that the ±5 percent of 50 percent of the maximum fuel input rate cannot be set, provided this minimum rate is no greater than 2⁄3 of the maximum input rate of the heater.

4.2.4.2 For manually controlled heater with one single firing rate the weighted average steady-state efficiency is the steady-state efficiency measured at the single firing rate.

4.2.5 Part-load fuel utilization efficiency. Calculate the part-load fuel utilization efficiency (ηu) expressed as a percent and defined as:

ηu = ηSS-WT−LI,ON

where:

ηSS-WT = as defined in 4.2.4 of this appendix

LI,ON = as defined in 4.2.3 of this appendix

4.2.6 Annual Fuel Utilization Efficiency.

4.2.6.1 For manually controlled vented heaters, calculate the AFUE expressed as a percent and defined as:

where:

2,950 = average number of heating degree days

ηSS = as defined as ηSS−WT in 4.2.4 of this appendix

ηu = as defined in 4.2.5 of this appendix

Qin−max = as defined as Qin at the maximum fuel input rate, as defined in 3.1 of this appendix

4,600 = average number of non-heating season hours per year

QP = as defined in 3.5 of this appendix

2.083 = (65 − 15) / 24 = 50 / 24

65 = degree day base temperature, °F

15 = national average outdoor design temperature for vented heaters as defined in section 4.1.10 of this appendix

24 = number of hours in a day

4.2.6.2 For manually controlled vented heaters where the pilot light can be turned off by the user when the heater is not in use as described in section 3.5.2, calculate the AFUE expressed as a percent and defined as:

AFUE=ηu

where:

ηu = as defined in section 4.2.5 of this appendix

4.3   Annual fuel utilization efficiency by the tracer gas method. The annual fuel utilization efficiency shall be determined by the following tracer gas method for all vented heaters equipped with thermal stack dampers.

4.3.1   On-cycle sensible heat loss. For vented heaters equipped with single-stage thermostats, calculate the on-cycle sensible heat loss (LS,ON) expressed as a percent and defined as:

LS,ON = LS,SS,A

where:

LS,SS,A = as defined in section 4.1.9 of this appendix

For vented heaters equipped with two stage thermostats, calculate LS,ON defined as:

LS,ON = X1LS,SS,A-red + X2LS,SS,A-max

where:

X1 = as defined in section 4.1.14 of this appendix

LS,SS,A-red = as defined as LS,SS,A in section 4.1.9 of this appendix at the reduced fuel input rate

X2 = as defined in section 4.1.15 of this appendix

LS,SS,A-max = as defined as LS,SS,A in section 4.1.9 of this appendix at the maximum fuel input rate

For vented heaters with step-modulating controls, calculate LS,ON defined as:

LS,ON = X1LS,SS,A-red + X2LS,SS,A-avg

where:

X1 = as defined in section 4.1.14 of this appendix

LLS,SS,A-red = as defined in section 4.3.1 of this appendix

X2 = as defined in section 4.1.15 of this appendix

LS,SS,A-avg = average sensible heat loss for step-modulating vented heaters operating in the modulating mode

where:

LS,SS,A-avg = as defined in section 4.3.1 of this appendix

TC = as defined in section 4.1.10 of this appendix

TOA* = as defined in section 4.1.10 of this appendix

15 = as defined in section 4.1.10 of this appendix

4.3.2   On-cycle infiltration heat loss. For vented heaters equipped with single-stage thermostats, calculate the on-cycle infiltration heat loss (LI,ON) expressed as a percent and defined as:

LI,ON = KI,ON(70−45)

where:

KI,ON = as defined in section 4.2.2 of this appendix

70 = as defined in section 4.2.3 of this appendix

45 = as defined in section 4.2.3 of this appendix

For vented heaters equipped with two stage thermostats, calculate LI,ON defined as:

LI,ON = X1KI,ON-Max(70−TOA*) + X2KI,ON,red(70−TOA)

where:

X1 = as defined in section 4.1.14 of this appendix

KI,ON-max = as defined as KI,ON in section 4.2.2 of this appendix at the maximum heat input rate

70 = as defined in section 4.2.3 of this appendix

TOA* = as defined in section 4.3.4 of this appendix

KI,ON,red = as defined as KI,ON in section 4.2.2 of this appendix at the minimum heat input rate

TOA = as defined in section 4.3.4 of this appendix

X2 = as defined in section 4.1.15 of this appendix

For vented heaters equipped with step-modulating thermostats, calculate LI,ON defined as:

LI,ON = X1KI,ON-avg(70−TOA*) + X2KI,ON,red(70−TOA)

where:

X1 = as defined in section 4.1.14 of this appendix

70 = as defined in section 4.2.3 of this appendix

TOA* = as defined in section 4.3.4 of this appendix

X2 = as defined in section 4.1.15 of this appendix

TOA = as defined in section 4.3.4 of this appendix

4.3.3   Off-cycle sensible heat loss. For vented heaters equipped with single-stage thermostats, calculate the off-cycle sensible heat loss (LS,OFF) at the maximum fuel input rate. For vented heaters equipped with step-modulating thermostats, calculate LS,OFF defined as:

LS,OFF = X1 LS,OFF,red

where:

X1 = as defined in section 4.1.14 of this appendix, and

LS,OFF,red = as defined as LS,OFF in section 4.3.3 of this appendix at the reduced fuel input rate.

For vented heaters equipped with two stage controls, calculate LS,OFF defined as:

LS,OFF = X1 LS,OFF,red + X2 LS,OFF,Max

where:

X1 = as defined in section 4.1.14 of this appendix,

LS,OFF,red = as defined as LS,OFF in section 4.3.3 of this appendix at the reduced fuel input rate,

X2 = as defined in section 4.1.15 of this appendix, and

LS,OFF,Max = as defined as LS,OFF in section 4.3.3 of this appendix at the maximum fuel input rate.

Calculate the off-cycle sensible heat loss (LS,OFF) expressed as a percent and defined as:

where:

100 = conversion factor for percent,

0.24 = specific heat of air in Btu per pound— °F,

Qin = fuel input rate, as defined in section 3.1 of this appendix in Btu per minute (as appropriate for the firing rate),

ton = average burner on-time per cycle and is 20 minutes,

Σ mS,OFF (TS,OFF −TRA) = summation of the ten values (for single-stage or step-modulating models) or twenty values (for two tage models) of the quantity, mS,OFF (TS,OFF −TRA), measured in accordance with section 3.3 of this appendix, and

mS,OFF = stack gas mass flow rate pounds per minute.

TS,OFF = stack gas temperature measured in accordance with section 3.3 of this appendix,

TRA = average room temperature measured in accordance with section 3.3 of this appendix,

PB = barometric pressure in inches of mercury,

VT = flow rate of the tracer gas through the stack in cubic feet per minute,

CT* = concentration by volume of the active tracer gas in the mixture in percent and is 100 when the tracer gas is a single component gas,

CT = concentration by volume of the active tracer gas in the diluted stack gas in percent,

TT = temperature of the tracer gas entering the flow meter in degrees Fahrenheit, and

(TT + 460) = absolute temperature of the tracer gas entering the flow meter in degrees Rankine.

4.3.4   Average outdoor temperature. For vented heaters equipped with single-stage thermostats, the average outdoor temperature (TOA) is 45 °F. For vented heaters equipped with either two stage thermostats or step-modulating thermostats, TOA during the reduced operating mode is obtained from Table 3 or Figure 1 of this appendix. For vented heaters equipped with two stage thermostats, TOA* during the maximum operating mode is obtained from Table 3 or Figure 1 of this appendix.

4.3.5   Off-cycle infiltration heat loss. For vented heaters equipped with single stage thermostats, calculate the off-cycle infiltration heat loss (LI,OFF) at the maximum fuel input rate. For vented heaters equipped with step-modulating thermostats, calculate LI,OFF defined as:

LI,OFF = X1LI,OFF,red

where:

X1 = as defined in section 4.1.14 of this appendix

LI,OFF,red = as defined in LI,OFF in section 4.3.5 of this appendix at the reduced fuel input rate

For vented heaters equipped with two stage thermostats, calculate LI,OFF defined as:

LI,OFF = X1LI,OFF,red + X2LI,OFF,max

where:

X1 = as defined in section 4.1.14 of this appendix

LI,OFF,red = as defined as LI,OFF in section 4.3.5 of this appendix at the reduced fuel input rate

X2 = as defined in section 4.1.15 of this appendix

LI,OFF,Max = as defined as LI,OFF in section 4.3.5 of this appendix at the maximum fuel input rate

Calculate the off-cycle infiltration heat loss (LI,OFF) expressed as a percent and defined as:

where:

100 = conversion factor for percent

0.24 = specific heat of air in Btu per pound— °F

1.3 = dimensionless factor for converting laboratory measured stack flow to typical field conditions

0.7 = infiltration parameter

70 = assumed average indoor air temperature, °F

TOA = average outdoor temperature as defined in section 4.3.4 of this appendix

Qin = fuel input rate, as defined in section 3.1 of this appendix in Btu per minute (as appropriate for the firing rate)

ton = average burner on-time per cycle and is 20 minutes

Σ mS,OFF = summation of the twenty values of the quantity, mS,OFF, measured in accordance with section 3.3 of this appendix

mS,OFF = as defined in section 4.3.3 of this appendix

4.3.6   Part-load fuel utilization efficiency. Calculate the part-load fuel utilization efficiency (ηu) expressed as a percent and defined as:

where:

Cj = 2.8, adjustment factor,

Lj = jacket loss as defined in section 4.1.5,

LL,A = Latent heat loss, as defined in section 4.1.6 of this appendix (for condensing vented heaters LL,A* for cyclic conditions),

ton = Average burner on time which is 20 minutes,

LS,ON = On-cycle sensible heat loss, as defined in section 4.3.1 of this appendix,

LS,OFF = Off-cycle sensible heat loss, as defined in section 4.3.3 of this appendix,

LI,ON = On-cycle infiltration heat loss, as defined in section 4.3.2 of this appendix,

LI,OFF = Off-cycle infiltration heat loss, as defined in section 4.3.5 of this appendix,

PF = Pilot fraction, as defined in section 4.1.4 of this appendix, and

tOFF = average burner off-time per cycle, which is 20 minutes.

4.3.7 Annual Fuel Utilization Efficiency.

Calculate the AFUE expressed as a percent and defined as:

where:

2,950 = average number of heating degree days

ηSS-WT = as defined in 4.1.16 of this appendix

ηu = as defined in 4.3.6 of this appendix

Qin−max = as defined in 4.2.6 of this appendix

4,600 = as specified in 4.2.6 of this appendix

QP = as defined in 3.5 of this appendix

2.083 = as specified in 4.2.6 of this appendix

4.4 Stack damper effectiveness for vented heaters equipped with electro-mechanical stack dampers. Determine the stack damper effectiveness for vented heaters equipped with electro-mechanical stack dampers (Do), defined as:

Do = 1.62 [1—AD cos Ω/AS]

where:

AD = as defined in 3.4 of this appendix

Ω = as defined in 3.4 of this appendix

AS = as defined in 3.4 of this appendix

4.5 Addition requirements for vented home heating equipment using indoor air for combustion and draft control. For vented home heating equipment using indoor air for combustion and draft control, DF, as described in section 4.1.2 of this appendix, and DS, as described in section 4.1.3 of this appendix, shall be determined from Table 1 of this appendix.

4.5.1   Optional procedure for determining DP for vented home heating equipment. Calculate the ratio (DP) of the rate of flue gas mass through the vented heater during the off-period, MF,OFF(TF,SS), to the rate of flue gas mass flow during the on-period, MF,SS(TF,SS), and defined as:

DP = MF,OFF(TF,SS)/MF,SS(TF,SS)

For vented heaters in which no draft is maintained during the steady-state or cool down tests, MF,OFF(TF,SS) is defined as:

For oil fueled vented heaters in which an imposed draft is maintained, as described in section 3.6 of this appendix, MF,OFF(TF,SS) is defined as:

MF,OFF(TF,SS) = MF,OFF(T*F,OFF)

where:

TF,SS = as defined in section 3.1.1 of this appendix,

T*F,OFF = flue gas temperature during the off-period measured in accordance with section 3.6 of this appendix in degrees Fahrenheit, and

TRA = as defined in section 2.9 of this appendix.

PB = barometric pressure measured in accordance with section 3.6 of this appendix in inches of mercury,

VT = flow rate of tracer gas through the vented heater measured in accordance with section 3.6 of this appendix in cubic feet per minute,

CT = concentration by volume of tracer gas present in the flue gas sample measured in accordance with section 3.6 of this appendix in percent,

CT* = concentration by volume of the active tracer gas in the mixture in percent and is 100 when the tracer gas is a single component gas,

TT = the temperature of the tracer gas entering the flow meter measured in accordance with section 3.6 of this appendix in degrees Fahrenheit, and

(TT + 460) = absolute temperature of the tracer gas entering the flow meter in degrees Rankine.

MF,SS(TF,SS) = Qin[RT,F(A/F) + 1]/[60HHVA]

Qin = as defined in section 3.1 of this appendix,

RT,F = as defined in section 4.1.7 of this appendix,

A/F = as defined in section 4.2.2 of this appendix, and

HHVA = as defined in section 4.2.2 of this appendix.

4.5.2   Optional procedure for determining off-cycle draft factor for flue gas flow for vented heaters. For systems numbered 1 through 10, calculate the off-cycle draft factor for flue gas flow (DF) defined as:

DF = DP

For systems numbered 11 or 12: DF = DP DO

For systems complying with section 3.6.1 or 3.6.2, DF = 0.05

Where:

DP = as defined in section 4.5.1. of this appendix, and

DO = as defined in section 4.4 of this appendix.

4.5.3   Optional procedure for determining off-cycle draft factor for stack gas flow for vented heaters. Calculate the off-cycle draft factor for stack gas flow (DS) defined as:

For systems numbered 1 or 2: DS = 1.0

For systems numbered 3 or 4: DS = (DP + 0.79)/1.4

For systems numbered 5 or 6: DS = DO

For systems numbered 7 or 8 and if DO(S/F)<1:DS = DO DP

For systems numbered 7 or 8 and if DO(S/F)>1:

DS = DO DP + [0.85−DO DP] [DO(S/F)−1]/[S/F−1]

where:

DP = as defined in section 4.5.1 or 3.6.1 of this appendix, as applicable

DO = as defined in section 4.4 of this appendix

4.6 Annual energy consumption.

4.6.1 National average number of burner operating hours. For vented heaters equipped with single stage controls or manual controls, the national average number of burner operating hours (BOH) is defined as:

BOHSS = 1,416AFA DHR−1,416 B

where:

1,416 = national average heating load hours for vented heaters based on 2,950 degree days and 15 °F outdoor design temperature

AF = 0.7067, adjustment factor to adjust the calculated design heating requirement and heating load hours to the actual heating load experienced by the heating system

DHR = typical design heating requirements based on QOUT, from Table 4 of this appendix.

QOUT = [(ηSS/100)−Cj (Lj/100)] Qin

Lj = jacket loss as defined in 4.1.5 of this appendix

Cj = 2.8, adjustment factor as defined in 4.3.6 of this appendix

ηSS = steady-state efficiency as defined in 4.1.10 of this appendix, percent

Qin = as defined in 3.1 of this appendix at the maximum fuel input rate

A = 100,000/[341,300PE + (Qin−QP)ηu]

B = 2.938(QP) ηu A/100,000

100,000 = factor that accounts for percent and kBtu

PE = as defined in 3.1.3 of this appendix

QP = as defined in 3.5 of this appendix

ηu = as defined in 4.3.6 of this appendix for vented heaters using the tracer gas method, percent

= as defined in 4.2.5 of this appendix for manually controlled vented heaters, percent

= 2,950 AFUEηSS Qin/[2,950 ηSS Qin—AFUE(2.083)(4,600)QP], for vented heaters equipped without manual controls and without thermal stack dampers and not using the optional tracer gas method, where:

AFUE = as defined in 4.1.17 of this appendix, percent

2,950 = average number of heating degree days as defined in 4.2.6 of this appendix

4,600 = average number of non-heating season hours per year as defined in 4.2.6 of this appendix

2.938 = (4,160/1,416) = ratio of the average length of the heating season in hours to the average heating load hours

2.083 = as specified in 4.2.6 of this appendix

4.6.1.1 For vented heaters equipped with two stage or step modulating controls the national average number of burner operating hours at the reduced operating mode is defined as:

BOHR = X1EM/Qred-in

where:

X1 = as defined in 4.1.14 of this appendix

Qred-in = as defined in 4.1.11 of this appendix

EM = average annual energy used during the heating season

= (Qin−QP)BOHSS + (8,760−4,600)QP

Qin = as defined in 3.1 of this appendix at the maximum fuel input rate

QP = as defined in 3.5 of this appendix

BOHSS = as defined in 4.6.1 of this appendix, in which the term PE in the factor A is increased by the factor R, which is defined in 3.1.3 of this appendix as:

R = 1.3 for two stage controls

= 1.4 for step modulating controls when the ratio of minimum-to-maximum fuel input is greater than or equal to 0.7

= 1.7 for step modulating controls when the ratio of minimum-to-maximum fuel input is less than 0.7 and greater than or equal to 0.5

= 2.2 for step modulating controls when the ratio of minimum-to-maximum fuel input is less than 0.5

A = 100,000/[341,300 PE R + (Qin − QP)ηu]

8,760 = total number of hours per year

4,600 = as specified in 4.2.6 of this appendix

4.6.1.2 For vented heaters equipped with two stage or step modulating controls the national average number of burner operating hours at the maximum operating mode (BOHH) is defined as:

BOHH = X2EM/Qin

where:

X2 = as defined in 4.1.15 of this appendix

EM = average annual energy used during the heating season

= (Qin−QP)BOHSS + (8,760−4,600)QP

Qin = as defined in 3.1 of this appendix at the maximum fuel input rate

4.6.2 Average annual fuel energy for gas or oil fueled vented heaters. For vented heaters equipped with single stage controls or manual controls, the average annual fuel energy consumption (EF) is expressed in Btu per year and defined as:

EF = BOHSS (Qin−QP) + 8,760 QP

where:

BOHSS = as defined in 4.6.1 of this appendix

Qin = as defined in 3.1 of this appendix

QP = as defined in 3.5 of this appendix

8,760 = as specified in 4.6.1 of this appendix

4.6.2.1 For vented heaters equipped with either two stage or step modulating controls EF is defined as:

EF = EM + 4,600QP

where:

EM = as defined in 4.6.1.2 of this appendix

4,600 = as specified 4.2.6 of this appendix

QP = as defined in 3.5 of this appendix

4.6.3 Average annual auxiliary electrical energy consumption for vented heaters. For vented heaters with single-stage controls or manual controls, the average annual auxiliary electrical consumption (EAE) is expressed in kilowatt-hours and defined as:

EAE = BOHSSPE + ESO

Where:

BOHSS = as defined in 4.6.1 of this appendix

PE = as defined in 3.1.3 of this appendix

ESO = as defined in 4.7 of this appendix

4.6.3.1 For vented heaters with two-stage or modulating controls, EAE is defined as:

EAE = (BOHR + BOHH)PE + ESO

Where:

BOHR = as defined in 4.6.1 of this appendix

BOHH = as defined in 4.6.1 of this appendix

PE = as defined in 3.1.3 of this appendix

ESO = as defined in 4.7 of this appendix

4.6.4 Average annual energy consumption for vented heaters located in a different geographic region of the United States and in buildings with different design heating requirements.

4.6.4.1 Average annual fuel energy consumption for gas or oil fueled vented home heaters located in a different geographic region of the United States and in buildings with different design heating requirements. For gas or oil fueled vented heaters the average annual fuel energy consumption for a specific geographic region and a specific typical design heating requirement (EFR) is expressed in Btu per year and defined as:

EFR = (EF−8,760 QP)(HLH/1,416) + 8,760QP

where:

EF = as defined in 4.6.2 of this appendix

8,760 = as specified in 4.6.1 of this appendix

QP = as defined in 3.5 of this appendix

HLH = heating load hours for a specific geographic region determined from the heating load hour map in Figure 3 of this appendix

1,416 = as specified in 4.6.1 of this appendix

4.6.4.2 Average annual auxiliary electrical energy consumption for gas or oil fueled vented home heaters located in a different geographic region of the United States and in buildings with different design heating requirements. For gas or oil fueled vented home heaters the average annual auxiliary electrical energy consumption for a specific geographic region and a specific typical design heating requirement (EAER) is expressed in kilowatt-hours and defined as:

EAER = EAE HLH/1,416

where:

EAE = as defined in 4.6.3 of this appendix

HLH = as defined in 4.6.4.1 of this appendix

1,416 = as specified in 4.6.1 of this appendix

4.7 Average annual electric standby mode and off mode energy consumption.

Calculate the annual electric standby mode and off mode energy consumption, ESO, defined as, in kilowatt-hours:

ESO = ((PW,SB * (4160—BOH)) + (PW,OFF * 4600)) * K

Where:

PW,SB = vented heater standby mode power, in watts, as measured in section 3.7 of this appendix

4160 = average heating season hours per year

PW,OFF = vented heater off mode power, in watts, as measured in section 3.7 of this appendix

4600 = average non-heating season hours per year

K = 0.001 kWh/Wh, conversion factor for watt-hours to kilowatt-hours

BOH = burner operating hours as calculated in section 4.6.1 of this appendix where for single-stage controls or manual controls vented heaters BOH = BOHSS and for vented heaters equipped with two-stage or modulating controls BOH = (BOHR + BOHH).

[49 FR 12169, Mar. 28, 1984, as amended at 62 FR 26162, May 12, 1997; 77 FR 74571, Dec. 17, 2012; 80 FR 806, Jan. 6, 2015]