80% vs 95% AFUE Furnace: What the Efficiency Rating Means

AFUE, annual fuel utilization efficiency, is the share of a furnace’s fuel energy that becomes heat over a heating season, so an 80% AFUE furnace turns about 80% of its fuel into heat and a 95% furnace about 95%. The federal minimum for most gas furnaces today is 80% AFUE. A Department of Energy (DOE) rule raises it to 95% for indoor and mobile home gas furnaces made from December 18, 2028, but as of September 29, 2026 that rule is back before an appeals court and DOE is weighing a petition to delay it.

What AFUE measures

AFUE is a seasonal average, not a snapshot. DOE’s Federal Energy Management Program defines it as the ratio of useful energy output to energy input, expressed as a percentage, over the entire heating season.

The rating comes from a federal test, and the Federal Trade Commission’s Energy Labeling Rule covers furnaces: manufacturers must make the EnergyGuide label for each model available on a publicly accessible website (16 CFR 305.22). That label is the place to confirm the AFUE a quote names.

The federal minimums today

The minimum depends on the fuel and on where the furnace sits. The current floors in 10 CFR 430.32 are:

• Non-weatherized gas furnace (installed indoors): 80% AFUE.
• Mobile home gas furnace: 80% AFUE.
• Weatherized gas furnace (installed outdoors): 81% AFUE.
• Non-weatherized oil furnace: 83% AFUE.
• Mobile home oil furnace: 75% AFUE.
• Weatherized oil furnace: 78% AFUE.

The 80% gas furnace floor has applied to units made since November 19, 2015.

Where the 95% rule stands on September 29, 2026

The rule exists but its future is open. DOE adopted it in a final rule published December 18, 2023: 95% AFUE for non-weatherized gas furnaces and mobile home gas furnaces, with compliance required from December 18, 2028. It appears in the current federal regulations, and DOE’s furnace page still lists that date.

Three later events matter:

• February 19, 2026: the American Gas Association, the American Public Gas Association and the National Propane Gas Association petitioned DOE to push the compliance date to January 1, 2030 at the earliest. DOE published the petition for comment on April 27, 2026, with comments due May 27, 2026.
• April 28, 2026: in a brief to the Supreme Court, the federal government said DOE has determined that the rules are factually and legally flawed and is considering a new rulemaking to correct them.
• June 8, 2026: in American Gas Association v. Department of Energy, the Supreme Court granted the petition, vacated the appeals court judgment that had upheld the rules, and sent the case back to the D.C. Circuit in light of the government’s position.

Two points hold whatever happens next. The rule applies to furnaces manufactured on or after the compliance date, so a furnace already in a house is not affected. And any change to the date or the level would come through a new DOE action or a court decision, both of which are public.

80% or 95%: non-condensing and condensing

The two efficiency tiers are different machines. DOE’s April 2026 notice describes the 95% level as one that effectively requires condensing technology, and according to DOE’s Federal Energy Management Program, furnaces that meet ENERGY STAR are condensing furnaces: they recover heat that would otherwise leave with the flue gas. The same guidance strongly recommends sealed combustion, explaining that condensing furnaces should not burn indoor air, because contaminants from common household products can corrode them.

That design changes the installation. Under the 2024 International Fuel Gas Code:

• A furnace vented with plastic pipe must be listed for it, and the manufacturer’s instructions must name the pipe material (Section 503.4.1).
• Provisions must be made to collect and dispose of condensate from the venting of condensing appliances (Section 503.9).
• When an appliance is permanently disconnected from an existing chimney or vent, that chimney or vent must be resized as necessary to control condensation and give the remaining appliances the draft they need (Section 501.15).

The last rule matters in houses where a water heater or boiler shares a chimney with the old furnace: disconnecting the furnace triggers the code’s resizing check for whatever stays on that chimney.

ENERGY STAR levels since July 31, 2026

ENERGY STAR raised its furnace requirement on July 31, 2026, when Version 5.0 of its specification took effect:

• Gas furnaces in the U.S. North: at least 97% AFUE.
• Gas furnaces in the U.S. South: at least 95% AFUE.
• Oil furnaces: at least 87% AFUE.
• Furnace air leakage (the specification’s Qleak): 2.0% or less.

A furnace qualifies under the specification in effect on its date of manufacture, so a unit built before July 31, 2026 may carry the label under the earlier specification.

ENERGY STAR’s North means states with 5,000 or more population-weighted heating degree days. The list includes, among others, Colorado, Illinois, Michigan, Minnesota, New Jersey, New York, Ohio, Pennsylvania, Washington and Wisconsin. The South includes Arizona, California, Florida, Georgia, Maryland, North Carolina, Texas and Virginia.

Choosing between them

ENERGY STAR sets a higher bar in the North, where the heating season is longer. Where the heating season is short, the difference between 80% and 95% applies to fewer hours of burning fuel.

The house often decides as much as the climate. A condensing furnace needs a route for a plastic vent to the outdoors, a place to drain condensate, and a plan for any appliance left on the old chimney. A contractor can tell after seeing the house whether those are simple or not.

Size matters for both types. ENERGY STAR’s design rules for new homes recommend a furnace output of 100% to 140% of the calculated heat loss, and DOE’s purchasing guidance lists oversizing among the installation problems that cause efficiency losses, occupant discomfort and shortened equipment life.

When a professional is needed, and what to ask

Replacing a gas furnace involves gas piping, venting and combustion safety. It is work for a qualified contractor, and the model International Residential Code requires a permit for it (Section R105.1). The questions below make two quotes comparable:

• What AFUE does the proposed furnace carry, and where is its EnergyGuide label?
• For a gas furnace in a northern state: does it meet ENERGY STAR Version 5.0, meaning 97% AFUE or higher?
• How will it vent? Where will the plastic vent run and end outdoors, and where will the condensate drain go?
• If a water heater or boiler stays on the old chimney, how will the chimney be checked and resized for it under Section 501.15 of the fuel gas code?
• Is the furnace sealed-combustion?
• What heat-loss calculation sets the size, and what percentage of that load is the proposed furnace’s output?
• Who obtains the permit, and when is the final inspection?