The 95% AFUE rule is a U.S. Department of Energy minimum-efficiency standard for residential gas furnaces. AFUE — Annual Fuel Utilization Efficiency — measures the share of fuel a furnace turns into usable heat over a heating season. The DOE published the final rule on December 18, 2023 under the Energy Policy and Conservation Act, codified at 10 CFR Part 430. It sets a minimum of 95% AFUE for new non-weatherized residential gas furnaces and mobile-home furnaces manufactured on or after December 18, 2028, five years after publication. The current federal minimum is 80% AFUE, so the rule is a substantial step up that, in practice, requires condensing furnace technology.
A furnace at 95% AFUE converts 95 cents of every fuel dollar into heat, versus 80 cents for a standard furnace. Reaching 95% requires a condensing design with a secondary heat exchanger that pulls heat from the exhaust until water vapor condenses out. That changes installation: a condensing furnace needs PVC venting and a condensate drain rather than a conventional metal flue, which can add cost in homes not already set up for it. The rule applies by date of manufacture, so it governs what factories may build after the compliance date, not what is already installed. It does not require anyone to replace a working 80% AFUE furnace, and units built before the date can still be sold and installed under normal sell-through.
The rule is finalized and remains in effect, but its legal footing is again unsettled. After the DOE issued the standard, a gas-industry coalition led by the American Gas Association petitioned the U.S. Court of Appeals for the D.C. Circuit to overturn it; in November 2025 the court upheld the standard in a 2-1 decision. The coalition then asked the U.S. Supreme Court to review that ruling, and on June 8, 2026 the Supreme Court vacated the D.C. Circuit decision and sent the case back for reconsideration in light of the federal administration's changed position. The Supreme Court did not strike down the furnace standard itself — the 95% AFUE rule remains in effect and the December 18, 2028 compliance date stands while the appeals court reconsiders, with no announced timeline. Because the compliance date is keyed to manufacture in late 2028, none of this affects furnaces sold or installed in 2026.
For a household replacing a furnace in 2026, the rule is the backdrop to the efficiency-tier decision rather than a hard constraint: an 80% AFUE furnace is still legal to buy and install today, but a 95%+ condensing furnace is where the federal minimum is headed and what a replacement done now can lock in. A high-efficiency 95%+ AFUE condensing furnace typically costs roughly $800 to $2,000 more than a standard model, and that gap reflects both the equipment and the PVC-venting and condensate-drain work — so the venting feasibility of the home is a real input, not a detail. In colder regions the fuel savings on a condensing unit pay that gap back faster; in milder Sun Belt markets with a low heating load the payback stretches out, which is why right-sizing with a Manual J load calculation matters more than chasing the top efficiency tier. Because the litigation is back before the D.C. Circuit, treat the 2028 date as the rule as finalized rather than a certainty, and ask the installer about venting before committing to a condensing furnace.