Section 431.76 - Uniform test method for the measurement of energy efficiency of commercial warm air furnaces(a)Scope. This section prescribes the test requirements used to measure the energy efficiency of commercial warm air furnaces with a rated maximum input of 225,000 Btu per hour or more.(b)Testing and calculations -(1) Thermal efficiency. Test in accordance with appendix A to subpart D of this part when making representations of thermal efficiency.(2)Thermal efficiency two. Test in accordance with appendix B to subpart D of this part when making representations of thermal efficiency two. 80 FR 42663 , July 17, 2015