AFUE Savings Calculator — Free Online Calculator
AFUE (Annual Fuel Utilization Efficiency) is the share of a furnace's fuel that becomes usable heat — a 95% furnace wastes 5%, an 80% furnace wastes 20%. This calculator compares two AFUE ratings and shows the annual fuel cost, dollar savings, and 15-year payoff of the more efficient furnace, so you can tell whether the upgrade pays for itself.
Comparing cooling instead? Use the SEER Savings Calculator. Need to size the furnace first? Use the Furnace BTU Calculator.
Compare two AFUE ratings
Older furnaces: 60–70% · 2015+ minimum: 80%
Condensing furnaces: 90–98.5%
You'd save every year
At 80% AFUE
$1,500/yr
At 95% AFUE
$1,263/yr
Over a 15-year lifespan
$3,553 saved · 15.8% less fuel
See the breakdown
Estimates assume rated AFUE and steady output; real use varies with weather, thermostat habits, and duct losses.
Annual heating cost by AFUE (quick reference)
80,000 BTU furnace · 1,000 full-load hours/yr · $1.50/therm. Your numbers scale with size, climate, and gas price.
| AFUE rating | Fuel used | Annual cost | vs. 80% |
|---|---|---|---|
| 80% (older / 2015 minimum) | 1,000 therms | $1,500 | — |
| 90% | 889 therms | $1,333 | save $167/yr |
| 92% | 870 therms | $1,304 | save $196/yr |
| 95% (2028 standard) | 842 therms | $1,263 | save $237/yr |
| 96% | 833 therms | $1,250 | save $250/yr |
| 98% | 816 therms | $1,224 | save $276/yr |
Estimates for comparison only. Actual usage varies with weather, home condition, and how you run your thermostat.
Sources & standards: U.S. DOE — finalized 95% AFUE furnace standard (Dec 2028), U.S. DOE Energy Saver — Furnaces & Boilers (AFUE 80–98.5%), U.S. EIA — residential natural gas prices.
The formula, explained in plain English
AFUE is just "heat delivered per fuel burned." Once you know that, the savings math is three short steps — and one elegant shortcut.
What AFUE means
The % of fuel energy that becomes heat over a season. A 90% AFUE furnace turns 90% of the gas into heat and sends the other 10% up the flue.
Why ÷ (AFUE/100)?
You must burn more fuel than the heat you actually need, because some is wasted. A lower AFUE burns more fuel for the same warmth.
The 95% rule
Today's minimum is 80% AFUE. The U.S. DOE's finalized standard raises it to 95% AFUE for new non-weatherized gas furnaces effective December 2028.
Condensing furnaces
90–98.5% AFUE models add a second heat exchanger to capture flue heat. They need a condensate drain and PVC venting to handle the cooler exhaust.
Worked examples
Three common upgrade decisions — including one where the upgrade isn't obviously worth it.
Replacing an old furnace — 80% → 95%, 80,000 BTU, moderate climate (1,000 hrs)
80,000 BTU output · $1.50/therm.
old: 800 ÷ 0.80 = 1,000 therms → $1,500/yr
new: 800 ÷ 0.95 = 842 therms → $1,263/yr
savings = $237/yr · 15.8% less fuel
Result: about $237 per year, roughly $3,550 over 15 years — a strong tailwind on top of replacing a furnace that was due anyway.
Cold climate, big furnace — 80% → 96%, 100,000 BTU, 1,800 hrs
100,000 BTU output · $1.50/therm.
old: 1,800 ÷ 0.80 = 2,250 therms → $3,375/yr
new: 1,800 ÷ 0.96 = 1,875 therms → $2,813/yr
savings = $562/yr · 16.7% less fuel
Result: about $562 a year — efficiency pays fastest where winters are long and the furnace runs the most hours.
The honest case — 92% → 96%, small 60,000 BTU, mild climate (600 hrs)
60,000 BTU output · $1.50/therm.
92%: 360 ÷ 0.92 = 391 therms → $587/yr
96%: 360 ÷ 0.96 = 375 therms → $563/yr
savings = $24/yr · 4.2% less fuel
Result: about $24 a year. Replacing a working 92% furnace just to reach 96% won't pay back on fuel alone — efficiency pays best on big systems, long winters, or furnaces already due for replacement.
Frequently asked questions
Common questions about AFUE ratings and furnace efficiency savings.
What is AFUE?
Annual Fuel Utilization Efficiency: the percentage of a furnace's fuel energy that becomes usable heat over a full season. 95% AFUE means 95% of the gas becomes heat and 5% is lost up the flue.
How much does upgrading from 80% to 95% AFUE save?
It cuts fuel use about 15.8% (1 − 80/95). For an 80,000 BTU furnace running 1,000 hours a year at $1.50/therm that's roughly $237/year, or about $3,550 over a 15-year life.
What's the formula for AFUE savings?
% fuel saved = 1 − (old AFUE ÷ new AFUE). For dollars: output therms = furnace BTU × heating hours ÷ 100,000; input therms = output ÷ (AFUE ÷ 100); multiply by your $/therm and subtract. The calculator above runs all of it instantly.
What AFUE should I buy?
Today's minimum is 80%. The U.S. DOE has finalized a 95% AFUE minimum for new non-weatherized gas furnaces effective December 2028, so a 95–96% condensing furnace is the future-proof choice for most homes — especially in cold climates.
Is a 96% AFUE furnace worth it over 80%?
Usually yes when you're replacing the furnace anyway: the fuel savings (~17%) plus the coming 95% standard make condensing furnaces the default. Replacing a healthy 90%+ furnace just to gain a few points rarely pays back on fuel alone.
Does AFUE apply to electric furnaces or heat pumps?
No. AFUE rates fuel-burning furnaces and boilers. Electric furnaces are nearly 100% efficient at the unit but expensive to run; heat pump heating is rated by HSPF — use our HSPF Savings Calculator or Operating Cost Calculator to compare fuels.
What's a condensing furnace?
A 90%+ AFUE furnace with a second heat exchanger that pulls extra heat from the exhaust, condensing its water vapor. It vents through PVC and needs a condensate drain, but wrings far more heat from the same gas.
Selling the high-efficiency upgrade? Quote it in seconds.
Energy savings win the conversation — a fast, professional estimate wins the job. TradesQuote turns the full replacement into a line-item quote: equipment, labor, materials, and disposal, with quantities, unit prices, and totals validated by a built-in quality control agent.
AI line-item estimates
Quantities, unit prices, and totals generated instantly.
Knowledge base
Upload past jobs so estimates reflect your real pricing.
Shareable & signable
Clients review, accept, and sign from a public link.
No credit card required · 14-day free trial · Cancel anytime