The Department of Energy has withdrawn the only federal test procedure that would have measured how commercial warm air furnaces perform at part load and how much heat they lose through the cabinet. A final rule published Oct. 7 deletes the method, known as Thermal Efficiency Two or TE2, from 10 CFR part 431. It takes effect Dec. 7.
For anyone specifying or installing gas-fired rooftop units, the practical result is that the federal efficiency number on a commercial furnace stays what it has been: thermal efficiency under the older appendix A test. A second, tougher metric won’t arrive.
What the TE2 furnace test procedure would have measured
DOE adopted TE2 as appendix B in June 2023, reasoning then that the industry test didn’t reflect a representative use cycle because it left out jacket losses and part-load operation. Use of appendix B was never mandatory. It would have become so only when DOE set an efficiency standard written in TE2 terms, and no such standard was adopted.
The department proposed pulling the method in May 2025 and now says it lacked the “clear and convincing evidence” the statute requires to depart from the industry test procedure referenced in ASHRAE Standard 90.1. Its stated conclusion: an uncertain gain in representativeness doesn’t outweigh a likely increase in burden. The rule removes the TE2 definition and appendix B and leaves appendix A as the required method.
Manufacturers’ numbers on commercial furnace testing costs
Ten parties filed written comments. Five supported withdrawal: AAON, Johnson Controls, Rheem, Trane and the trade group AHRI. The opposition came from efficiency and environmental groups, including the Appliance Standards Awareness Project, ACEEE, the Center for Biological Diversity and the Northwest Energy Efficiency Alliance, along with a group of state agencies.
The cost figures in the record are the manufacturers’ own. Trane told DOE that appendix A takes three to four weeks of setup per unit and appendix B would add roughly four more, at an added cost of $6 million to $8 million across its configurations. One of its rooftop units, it said, needed 1,600 additional thermocouples for the jacket-loss test. Johnson Controls put its bill at more than $1 million and more than a year.
DOE didn’t publish an independent estimate in the rule. Neither side quantified the energy at stake. According to the rule, none of the opponents supplied a savings figure.
What specifiers lose without a part-load efficiency metric
That last point is the weak spot in both arguments. A furnace section in a rooftop unit sits outdoors, so cabinet heat loss goes straight to the weather, and a modulating furnace spends most of its hours below full fire. A full-load combustion number can’t tell two products apart on either count. Whether the difference is large enough to matter is exactly what a test would show, and now there won’t be a federal one.
Owners working toward building performance targets feel that gap first. Programs such as Maryland’s building energy performance standards score measured building performance, not nameplate ratings, and local reach codes in California push the same direction. Mechanical engineers who want part-load data on a gas heat section will have to ask each manufacturer for it and accept whatever method the manufacturer used.
The rooftop market has other things to worry about. The refrigerant phasedown is reshaping the cooling side of the same equipment. But a tighter furnace standard built on real operating conditions now needs a new test procedure rulemaking before it can even be proposed. Trane’s setup time alone was three to four weeks a unit. The regulatory clock runs slower than that.