How Much Does It Cost to Run a Furnace?
About $6.32 a day for a common 80,000 BTU/hr gas furnace at 95% AFUE, lit 5 hours and burning $1.50/therm gas — roughly $190 a month in the heating season. An electric furnace putting the same heat into the same ducts costs $544. Set your own furnace, runtime and fuel price below.
Fuel
The nameplate rating — gas burned per hour, not heat delivered.
Hours actually lit, not hours the thermostat is on. A cycling furnace fires a fraction of the day.
76,000 BTU/hr of heat reaches the ducts; the rest goes up the flue.
On your gas bill. Gas prices swing far more by region and season than electricity does.
A gas furnace still runs an electric blower on every call for heat.
A single-speed PSC motor draws about 400 W; a variable-speed ECM nearer 150 W. Worth $0.32 a day here.
Cost to run this furnace, per day
$6.32
5 hours of burner runtime at $1.26 an hour — $189.60 a month, or $948.00 across a 5-month heating season.
Gas burned
4.0 therms
a day, plus 2.0 kWh for the blower
Heat delivered
380k BTU
a day, at 76,000 BTU/hr into the ducts
Price of that heat
$16.63
per million BTU delivered — the number that compares fuels
80,000 BTU/hr ÷ 100,000 = 0.80 therms an hour × $1.50 = $1.20, plus $0.06 of blower × 5 hours = $6.32 a day. Raise the AFUE and this figure does not move — the furnace burns the same gas per hour. What moves is the heat you get for it.
What the same heat would cost on an electric furnace
To put the same 76,000 BTU/hr into the ducts, an electric furnace needs 22.3 kW of elements and would cost $544.18 a month against this furnace's $189.60 — $47.74 per million BTU against $16.63. Staying on gas saves $354.58 a month. At $0.16/kWh, gas stops being the cheaper heat once it passes $4.45/therm.
Check the runtime against your own gas bill
Implied burner runtime
150 h · 5.0 h/day
A 80,000 BTU/hr furnace burns 0.80 therms an hour, so 120 therms is 150 hours of flame. Subtract any other gas appliances from the bill first — a gas water heater is usually the big one — and put the result into the runtime box above for a figure that is yours rather than ours.
Nameplate BTU is fuel input. Heat delivered is input × AFUE, with electric resistance treated as 100% AFUE because it has no flue. A therm is 100,000 BTU; a kWh is 3,412 BTU. Monthly figures use a 30-day month and a 5-month heating season. The blower is charged at 400 W on every burner hour, on either fuel; because it sits in the airstream its waste heat reaches the house anyway, so that is a slightly conservative assumption. Gas at $1.50/therm is a starting point to overwrite, not a claim about your utility. Nothing here includes equipment or installation. Not sure of your electricity rate? Check average rates by state.
How much does it cost to run a gas furnace?
Daily cost = nameplate BTU/hr ÷ 100,000 × price per therm × burner hours, plus the blower
Two things trip people up here, and they pull in opposite directions. The BTU on the nameplate is fuel going in, not heat coming out — so it, and not AFUE, sets what an hour of burning costs. And “hours” means burner runtime, not the hours the thermostat is switched on. A furnace cycles; it is lit for a fraction of the winter.
Worked example (80,000 BTU/hr at 95% AFUE, 5 hours, $1.50/therm, 400 W blower at $0.16/kWh): 80,000 ÷ 100,000 = 0.80therms an hour × $1.50 = $1.20, plus $0.06 of blower, is $1.26 an hour. Over 5 hours that is $6.32 per day, or $189.60 over a 30-day month.
Daily cost by burner runtime and gas price
Rows are hours the burner is actually lit. Columns are gas prices, which swing far more by region and season than electricity does. All figures are for an 80,000 BTU/hr furnace with its blower running.
| Burner runtime | $1.00/therm | $1.50/thermDefault | $2.00/therm | $2.50/therm |
|---|---|---|---|---|
| 1 hour a day | $0.86 | $1.26 | $1.66 | $2.06 |
| 2 hours a day | $1.73 | $2.53 | $3.33 | $4.13 |
| 5 hours a dayTypical cold-month average | $4.32 | $6.32 | $8.32 | $10.32 |
| 8 hours a day | $6.91 | $10.11 | $13.31 | $16.51 |
| 12 hours a day | $10.37 | $15.17 | $19.97 | $24.77 |
| 24 hours a dayContinuous — a furnace that never satisfies | $20.74 | $30.34 | $39.94 | $49.54 |
The blower is charged at 400 W on every burner hour, which is $0.06 an hour at $0.16/kWh — a single-speed PSC motor. A variable-speed ECM blower draws nearer 150 W. Find your electricity rate on the rates by state page.
How to find your real burner runtime
Do not guess it — read it off the gas bill. Your furnace burns 0.80 therms an hour, so therms billed ÷ 0.80 is the number of hours it was lit. A bill showing 120 therms of heating gas means 150 hours of flame, or 5.0 hours a day. Subtract any other gas appliances first; a gas water heater is usually the big one. The calculator above will do this for you.
Gas vs. electric furnace running costs
Gas is billed per therm and electricity per kilowatt-hour, so the two can only be compared in the currency the house cares about: heat delivered. Every row below puts the same 380,000 BTU into the ducts each day — the output of our 80,000 BTU/hr furnace over 5 hours — and differs only in what that costs. Less efficient furnaces meet the demand by running longer.
| Furnace | Runtime a day | Fuel a day | Per million BTU | Per month | Per season |
|---|---|---|---|---|---|
| Gas, 80% AFUENon-condensing — vents through a metal flue | 5.9 h | 4.75 therms | $19.75 | $225.15 | $1126 |
| Gas, 90% AFUEEntry-level condensing — vents through PVC | 5.3 h | 4.22 therms | $17.56 | $200.13 | $1001 |
| Gas, 95% AFUEThe common high-efficiency unit | 5.0 h | 4.00 therms | $16.63 | $189.60 | $948 |
| Gas, 98% AFUETop of the condensing range | 4.8 h | 3.88 therms | $16.12 | $183.80 | $919 |
| Electric, 100% AFUE22.3 kW of resistance elements | 5.0 h | 111 kWh | $47.74 | $544.18 | $2721 |
Gas at $1.50/therm, electricity at $0.16/kWh, a 400 W blower on every row, a 30-day month and a 5-month season. Fuel only — equipment and installation are outside this comparison. Note that the gas rows all burn 0.80 therms an hour: a higher AFUE does not make the flame cheaper, it makes the flame shorter.
The two numbers worth remembering
A million BTU of heat costs $16.63 from the gas furnace and $47.74 from the electric one — a factor of 2.9. Gas stops winning only above $4.45/therm, or if electricity drops below $0.054/kWh — a rate no state averages. Idaho, the cheapest, is $0.10, nearly twice it. Because both furnaces deliver the same heat they run the same hours, so the blower cancels out of both sides and these break-evens depend on fuel prices alone.
The efficient furnace is the expensive one
The electric furnace is 100% efficient. It has no flue, so nothing is thrown away — every kilowatt-hour becomes heat in the duct. It is also 2.9 times dearer to feed, because a BTU bought as electricity simply costs more than a BTU bought as gas. Efficiency describes what a machine does with the energy you buy; it says nothing about what that energy cost. This is the single most common confusion in heating, and it is why efficiency ratings can never be compared across fuels.
A whole-home electric furnace is a wiring problem too
Matching 76,000 BTU/hr with resistance elements takes 22.3 kW, which pulls 93 amps continuously at 240 volts. The NEC sizes a continuous load at 125% of its current, so that wants a 116 A circuit — larger, on its own, than the entire electrical service in many older homes. Our electric furnace appliance page models a more typical 10 kW unit at $9.60 a day — but 10 kW is only 34,120 BTU/hr, well under half the heat of the gas furnace above. That is the honest reason the two pages disagree.
Does a higher-AFUE furnace pay for itself?
AFUE is the share of the fuel that becomes heat in the house rather than exhaust up the flue. Going from 80% to 95% cuts gas use by exactly 1 − 80/95, or 15.8% — no more and no less, whatever the weather does.
80% AFUE, per season
$1126
95% AFUE, per season
$948
Saved per season
$178
That saving is real and it recurs every winter. It is also a small fraction of what a furnace costs installed, so on fuel savings alone the payback runs to many seasons — and an old furnace that still works owes you nothing. The moment to buy efficiency is the moment the old unit fails and you are writing a cheque for a furnace regardless. Until then the money is on the demand side: sealing, insulation and the thermostat all cut burner hours for a fraction of what a furnace costs.
How to reduce your heating bill
Everything on this page multiplies burner hours by the cost of an hour. You cannot do much about the cost of an hour — it is the gas price and the nameplate. Burner hours are where the money is, and every item below takes hours off.
Turn the thermostat down, and set it back
Heat loss is proportional to the temperature difference across the walls, so a lower setpoint means a smaller difference and fewer burner hours. Setting back overnight and while the house is empty costs nothing to do — the furnace makes up the difference more cheaply than it would have spent holding the temperature.
Change the filter
A clogged filter makes the blower work against a restriction and slows the airflow across the heat exchanger, which lengthens every cycle. It is the cheapest maintenance in the house and the one most often skipped.
Seal the ducts before anything else
Ducts running through an unheated attic or crawlspace leak heat you have already paid to make. Sealing and insulating those runs cuts burner hours without touching the furnace, the thermostat, or your comfort.
Stop the air leaks
Weatherstripping, caulk and attic-hatch insulation reduce the heat the house sheds, which is the demand your furnace exists to meet. A tighter envelope is the one upgrade that pays off on every fuel and every future furnace. More in our energy savings guide.
Do not zone-heat on top of central heat
A space heater only saves money if the central thermostat comes down as it goes on. Run one alongside a furnace at its usual setpoint and you have simply added a 1.5 kW load to the bill.
Price a heat pump before you replace
A heat pump moves heat rather than making it, so it delivers several units of heat per unit of electricity — which is how electricity can beat gas despite costing $48 per million BTU as resistance heat. Our heat pump running costs page works the comparison against this furnace, and finds it closer than either camp admits.
Related Guides
Cost to Run a Space Heater
When heating one room beats heating the whole house
Cost to Run a Heat Pump
The electric alternative, priced per BTU against this furnace
Space Heater vs. Central Heat
Heat pump, gas furnace and electric furnace compared per room
Electric Furnace Cost Calculator
Quick watts-and-hours estimate on the main tool
Electricity Rates by State
What the blower — and any electric heat — really costs you
How to Save on Energy Bills
Practical tips by room with savings
Compare Appliance Costs
See how heating stacks up against everything else you run
Frequently Asked Questions
How much does it cost to run a gas furnace all day?
Taken literally — the burner lit for all 24 hours — a 80,000 BTU/hr furnace at 95% AFUE costs about $30.34 a day at $1.50/therm, blower included. Almost no furnace does that. A furnace cycles: it fires, satisfies the thermostat, and shuts off. On a genuinely cold day 8–12 hours of burner runtime is a lot, which is $10.11–$15.17. On an average cold-month day it is nearer 5 hours, or $6.32. If your burner truly is lit 24 hours a day, the furnace is undersized for the weather or the house is losing heat as fast as it makes it — either way the fix is not on the thermostat.
How much does it cost to run an electric furnace?
Roughly 2.9 times what the equivalent gas furnace costs. To deliver the same 76,000 BTU/hr, an electric furnace needs 22.3 kW of resistance elements, which at the US average $0.16/kWh comes to $544.18 a month against the gas furnace's $189.60. Smaller units cost proportionally less: our electric furnace appliance page models a 10 kW unit for 6 hours a day, which is $9.60 a day — but 10 kW is only 34,120 BTU/hr, well under half the heat of the gas furnace above.
Is a gas furnace cheaper to run than an electric furnace?
At typical US prices, by a wide margin — about 2.9 to one. A million BTU of heat costs $16.63 from a 95% AFUE gas furnace at $1.50/therm, and $47.74 from an electric furnace at $0.16/kWh. Gas only loses if it passes $4.45/therm, or if electricity falls below $0.054/kWh — and no state average is close to the latter. Idaho, the cheapest, is $0.10. Note that the electric furnace is the more efficient machine of the two: it wastes nothing up a flue. Efficiency and cheapness are different questions.
How many therms does a furnace use per hour?
Divide the nameplate BTU/hr by 100,000, because a therm is 100,000 BTU by definition. A 80,000 BTU/hr furnace burns 0.80 therms an hour of burner runtime, whatever its AFUE — efficiency changes the heat you get out, not the gas that goes in. This also runs backwards, which is the most useful thing on this page: 120 therms of heating gas on a bill means 150 hours the burner was lit, or 5.0 hours a day. Subtract other gas appliances first — a gas water heater is usually the big one.
Does a 95% AFUE furnace really save money over an 80%?
It cuts gas use by 15.8%, which is exactly 1 − 80/95. Over a 5-month season heating the same house, that is $948 instead of $1126 — about $178 saved. Worth having, but it is a fraction of what a replacement furnace costs installed, so on fuel savings alone the payback runs to many seasons. The time to buy the efficient furnace is when the old one has failed and you are buying a furnace regardless.
Why is the BTU number on my furnace not the heat it produces?
Because it is the fuel going in, not the heat coming out. A 80,000 BTU/hr gas furnace burns that much gas an hour; at 95% AFUE, 76,000 BTU/hr of it reaches the ducts and the rest leaves up the flue. This is why raising AFUE does not lower your cost per hour — the burner consumes the same gas — it lowers the hours the burner has to run. Electric furnaces are the exception: they have no flue, so input and output are the same number.