Within the funds available to a PHA, energy conservation measures should be accomplished with the shortest pay-back periods funded first. A PHA may make adjustments to this funding order because of insufficient funds to accomplish high-cost energy conservation measures (ECM) or where an ECM with a longer pay-back period can be more efficiently installed in conjunction with other planned modernization. A PHA may not install individual utility meters that measure the energy or fuel used for space heating in dwelling units that need substantial weatherization, when installation of meters would result in economic hardship for residents. In these cases, the ECMs related to weatherization shall be accomplished before the installation of individual utility meters.