Free tool
See what your gas, propane, oil or electric furnace costs to run per hour, day and month, and what it costs to run the furnace fan all the time.
For gas, propane and oil: cost per hour = input BTU ÷ BTU per unit of fuel × price per unit. The calculator uses 100,000 BTU per therm of natural gas, about 91,500 BTU per gallon of propane and about 138,500 BTU per gallon of heating oil. For an electric furnace: kilowatts × price per kWh.
Multiply by the hours the burner runs each day. That figure is not the same as hours of heat. The burner cycles on and off, so a furnace that heats all day may run only 8 hours.
The default prices are examples. Replace them with the price on your latest bill or delivery receipt.
A gas furnace with an 80,000 BTU input burns 0.8 therms an hour. At $1.50 a therm that is about $1.20 an hour while the burner is on. Your price and furnace size change the answer.
A 500 watt blower used 24 hours a day for 30 days uses 360 kWh. At 17 cents per kWh that is about $61 a month. A newer ECM motor at 150 watts costs about a third of that.
Not the fuel burned per hour. An efficient furnace turns more of that fuel into heat, so it runs for fewer hours to warm the same house.
On the rating plate inside the furnace door. Look for Input in BTU per hour, or Output for the heat delivered. Electric furnaces list kilowatts.
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On the furnace label as Input. Common sizes are 40,000 to 120,000.
On your bill. 1 CCF is close to 1 therm. The default is only an example.
How long the furnace actually runs in a day, not how long the heat is on. It is often 6 to 12 hours in cold weather.
Per hour of running
$1.20
Per day
$9.60
Per month (30 days)
$288
Formula: input BTU ÷ BTU per unit of fuel × fuel price, times hours run. Cost is based on the fuel you burn, so efficiency changes how much heat you get, not how much fuel the burner uses while it is on. Your real bill also depends on the blower, the weather and how often the thermostat calls for heat.
Look at the motor label. Older PSC motors often use 400 to 700 W, newer ECM motors often 100 to 250 W.
Per hour
$0.085
Per day (24 h)
$2.04
Per month, fan always on
$61.20
Fan-only use of 500 W draws 360 kWh a month.