14 CFR § 25.1101
Carburetor air preheater design
July 13, 2020
Each carburetor air preheater must be designed and constructed to—
(a) Ensure ventilation of the preheater when the engine is operated in cold air;
(b) Allow inspection of the exhaust manifold parts that it surrounds; and
(c) Allow inspection of critical parts of the preheater itself.