80% vs 96% furnace: what is the difference?

What AFUE means

AFUE stands for annual fuel utilization efficiency. ENERGY STAR defines it as, in general, the percentage of the heat in the incoming fuel that is converted to space heat instead of being lost.

So an 80% AFUE furnace turns about 80% of its gas into heat for the house and loses the rest, mostly out the exhaust. A 96% furnace loses about 4%. DOE's Energy Saver page calls 80% to 83% AFUE mid-efficiency and 90% to 98.5% AFUE high-efficiency condensing.

What the federal minimum is, and what is still unsettled

The federal efficiency table in 10 CFR 430.32 sets the minimum for non-weatherized gas furnaces at 80.0% AFUE for units manufactured on or after November 19, 2015. The same table lists 95.0% AFUE for units manufactured on and after December 18, 2028. So an 80% furnace is legal to buy today.

The 2028 date is not settled. As of October 22, 2026:

• DOE finalized the 95% standard in 2023. The CFR table shows the compliance date as December 18, 2028.
• In April 2026 DOE published a notice (91 FR 22477) asking for comment on a petition from the American Gas Association and the American Public Gas Association and the National Propane Gas Association. They asked DOE to move the furnace compliance date to January 1, 2030 at a minimum. DOE was seeking views on whether to grant it. Comments closed May 27, 2026.
• On June 8, 2026 the U.S. Supreme Court granted review in American Gas Association v. Department of Energy (No. 25-879), vacated the D.C. Circuit's November 2025 decision that had upheld the rule, and sent the case back for further consideration in light of the government's changed position. The Court did not strike down the standard. Holland & Knight says the standards remain in effect on remand.
• As of October 22, 2026 the CFR still lists December 18, 2028. DOE has said it is reconsidering the rule and, per ACHR News, has proposed delaying it while the case continues, but we found no final rule moving the date. It could change.

Venting: the biggest practical difference

An 80% furnace sends exhaust up a type B metal vent to the roof, according to a Washington Gas Light presentation given at a 2014 DOE workshop. DOE Energy Saver notes mid-efficiency units have a greater risk of depositing acidic condensation in chimneys.

A condensing furnace pulls extra heat out of the exhaust in a second heat exchanger. The same presentation says it requires PVC venting, will not connect to existing venting when replacing a furnace, and lists condensate disposal as a drawback. Lennox's manual for a condensing model says the connections are PVC and the condensate line must slope down to a drain, routed inside conditioned space to avoid freezing.

If your gas water heater shares the old furnace chimney, the same Lennox manual says the existing vent pipe for the other appliance must be checked, and that without the furnace's heat it is probably oversized. A contractor needs to check that before swapping equipment.

Safety: if you ever smell gas or suspect carbon monoxide, leave the house and call 911 or M.U.D. at 402.554.7777 from outside.

ENERGY STAR criteria for Nebraska and Iowa

ENERGY STAR puts Nebraska and Iowa in its U.S. North region. For the North, its key product criteria call for gas furnaces rated 97% AFUE or greater, plus no more than 2.0% air leakage. The U.S. South threshold is 95%.

So a 96% furnace does not meet the North criteria, and neither does an 80% one. Carrier's page for its Infinity 98 furnace says only certain sizes meet ENERGY STAR North (97%+).

Rebates in Omaha and Council Bluffs

M.U.D.'s rebate page currently lists no furnace rebate for single-family homes. Its furnace rebate, up to $500, is for developer and multi-family housing only, and the page says it does not apply to residential single-family dwellings. Offers change, so check M.U.D.'s rebate page before you buy.

MidAmerican Energy's Iowa residential page lists an instant discount of $2.40 per MBtuh for natural gas furnaces. It is available only through a participating provider, and equipment must be purchased, installed and operating between January 1 and December 31, 2026. MidAmerican's equipment qualifications sheet lists the furnace discount for gas furnaces rated 95% AFUE or higher, so an 80% unit would not qualify.

Omaha's winters and how to weigh it

The National Weather Service's Omaha monthly climate report for January 2026 lists the 1991 to 2020 normals for January as 15.2 degrees F (average low) and 33.6 degrees F (average high).

Higher AFUE means less fuel lost per unit of heat. We give no dollar savings figure because it depends on your house, your gas rate, and the installation. What you can compare:

• 80%: metal vent or chimney (a contractor must confirm yours can be reused), no condensate drain, more heat lost in exhaust.
• 90% to 96%: PVC venting and a condensate drain, less heat lost, new venting work likely.
• For pricing and sizing, see new furnace and AC cost in Omaha and what size furnace you need.

Compare quotes

Ask any contractor to itemize the venting work so quotes compare evenly. To reach one independent local contractor, get a free quote. We are a referral service, not an HVAC contractor.

Need a repair first? Start with furnace repair in Omaha.

Sources

• Furnaces Key Product Criteria (ENERGY STAR)
• 10 CFR 430.32, Energy and water conservation standards (eCFR)
• Energy Conservation Standards for Consumer Furnaces, final rule, 88 FR 87502 (Federal Register)
• Notification of Petition for Rulemaking, 91 FR 22477 (Federal Register)
• Docket No. 25-879, American Gas Association v. Department of Energy (Supreme Court of the United States)
• U.S. Supreme Court Reopens DOE's Rarely Challenged Efficiency Standards (Holland & Knight)
• 95% Furnace Efficiency Rule to Get New Hearing (ACHR News)
• Furnaces and Boilers (U.S. DOE Energy Saver)
• Workshop presentation, Kevin Dunn, Washington Gas Light, Oct. 9, 2014 (hosted by U.S. DOE)
• ML196UHEK installation instructions (Lennox)
• Infinity 98 Gas Furnace (Carrier)
• Rebates (M.U.D.)
• Iowa Residential Instant Discounts and Rebates (MidAmerican Energy)
• HVAC Instant Discount equipment qualifications (MidAmerican Energy)
• January 2026 Climate Report, Omaha (National Weather Service Omaha/Valley)