40,000 BTU furnaces
Every certified furnace at this input rating, gas and oil, ranked by AFUE — the share of fuel that becomes heat in the house.
Data current as of July 12, 2026 · 388 certified units · source AHRI + ENERGY STAR
Which efficiency tier is worth buying at this size?
Furnace installed cost tracks the efficiency tier, not the size — so the decision at any input rating is which tier to buy, and there are two steps. Running costs below come from the certified units at this size over a 40 MMBtu season, the default our operating-cost calculator uses.
Step 1 · 80% → condensing
15-year payback
About $2,000 more to install, saving $133 a year in gas. Inside the life of a furnace — this step is worth taking.
Step 2 · condensing → modulating
Never
Another $2,750 to install for $12 a year. The gas saving is nearly nothing because the first step already captured it — buy this tier for quiet, even heat and better humidity control, not for the bill.
At this size
210 of 388
certified units are condensing (90%+ AFUE), running about $707 a year against $840 for the 80% band.
Install bands are US national typical for a like-for-like swap, compiled 2026-07-16; a condensing furnace also needs new PVC venting and a condensate drain, which is part of why the step costs what it does. Gas cost per MMBtu is computed from certified AFUE and EIA average prices — see our methodology.
Highest AFUE in this group
GE NF97X040V3BR
AFUE 97.5 · $17.23 per MMBtu to run.
Not on Amazon. Sold through installers. You can buy the filter and a smart thermostat for it yourself.
AFUE is the share of fuel a furnace turns into heat in your home. 96% AFUE wastes 4 cents of every dollar.
Every unit here is the same input rating, so the ranking is efficiency at a fixed size. Sizing is a heat-loss calculation, not a rule of thumb — a bigger furnace short-cycles rather than heating better.
The 20 highest-AFUE of 388 certified units · 1 with a verified place to buy
| Brand & model | AFUE | Input | Fuel | $/MMBtu | Buy | |
|---|---|---|---|---|---|---|
| GE NF97X040V3BR | 97.5 | 40,000 BTU | Natural Gas, Propane Gas | $17.23 | installer | |
| PHANTOM B97UR402V3BX | 97.5 | 40,000 BTU | Natural Gas, Propane Gas | $17.23 | installer | |
| AIREASE A97US2V040B12X | 97.5 | 40,000 BTU | Natural Gas, Propane Gas | $17.23 | installer | |
| LENNOX SL297UH040NV36B | 97.5 | 40,000 BTU | Natural Gas, Propane Gas | $17.23 | installer | |
| DAIKIN DR96TC0403BN | 97.5 | 40,000 BTU | Natural Gas, Propane Gas | $17.23 | installer | |
| GOODMAN GRVT960403BN | 97.5 | 40,000 BTU | Natural Gas, Propane Gas | $17.23 | Buy | |
| THERMAL ZONE TZ97UP2V040B3SA | 97.0 | 42,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| FUJITSU FF97TV304017UPS | 97.0 | 42,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| DURASTAR DR97UPAW0402317S | 97.0 | 42,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| RHEEM R972V0403A17UPS | 97.0 | 42,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| LENNOX ML297UH045XV36B | 97.0 | 44,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| GE NF97U030T2BR | 97.0 | 30,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| GE NF97D045T3BR | 97.0 | 44,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| GE NF97U045T3BR | 97.0 | 44,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| GE NF97U045V3BR | 97.0 | 44,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| COMFORT-AIRE GUH97T045B3MP | 97.0 | 44,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| CONCORD 97G2UH030BE08 | 97.0 | 30,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| AIREASE A97UH2E030B08S | 97.0 | 30,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| PHANTOM B97DR452E3B | 97.0 | 44,000 BTU | Natural Gas, Propane Gas | $17.32 | installer | |
| PHANTOM B97UR452E3B | 97.0 | 44,000 BTU | Natural Gas, Propane Gas | $17.32 | installer |
Showing the top 20 by AFUE. All 388 certified units in this group are filterable in the full database — we rank here rather than dump, because a table nobody can read is not a resource.
Capacity and efficiency are AHRI-certified values; $/MMBtu is computed by us from EIA energy prices — see methodology. Input rating is the fuel the burner consumes; output is lower by exactly the AFUE.