The U.S. Supreme Court on June 8, 2026, vacated a D.C. Circuit decision that had upheld Department of Energy efficiency mandates for gas-fired furnaces and commercial water heaters, sending the case back to the appeals court for reconsideration. The high court's brief order directs the lower court to review its ruling in light of the Trump administration's stated position that the DOE rules 'rest on a legal error.'
The Biden-era rules would require residential furnaces manufactured after December 18, 2028, to meet a minimum 95% AFUE efficiency rating. Non-condensing furnaces — which dominate approximately 55% of the residential gas furnace market — cannot achieve that threshold without fundamentally changing their venting design. The practical effect would be to eliminate non-condensing furnaces from the new-equipment market.
Why it matters for contractors: Non-condensing furnace replacements are the single largest category of routine heating replacement work. They vent vertically, using existing chimney infrastructure. Condensing furnaces require horizontal PVC venting and condensate drainage — modifications that can add hundreds to thousands of dollars to a standard replacement job and are sometimes architecturally impossible in older homes.
If the mandates eventually take effect in their current form, replacement jobs that today take a few hours become multi-day renovations. Homeowners who can't afford the modifications face the prospect of having no compliant gas heating option. Trade groups including HARDI and PHCC have argued this outcome disproportionately affects low-income households and older housing stock.
What happens next: The case returns to the D.C. Circuit, which must now reconsider its prior ruling. The DOE under the Trump administration has signalled it is reviewing the efficiency standards and may delay or revise them. A delay of the October 2026 commercial water heater compliance date is considered likely. The 2028 residential furnace deadline is less immediately at risk but is now formally in play.
For distributors, the short-term signal is clear: current inventory of non-condensing furnaces remains sellable with no installation deadline, and the mandate's implementation timeline is increasingly uncertain. For contractors, the practical advice hasn't changed — know your venting options, be able to quote both condensing and non-condensing scenarios, and don't promise homeowners that non-condensing equipment will be permanently available.
