Space Heater vs Central Heat Cost Calculator
Compare heating one room with an electric space heater against heating the whole house with a gas furnace, at your state's electricity and natural-gas prices.
Space heater vs central heat cost
A19Scenario A
Sets the electricity rate. Pick US average if you're not sure.
From EIA for US average. Use the rate on your bill if you know it.
Rate used: 18.2¢/kWh · US average · EIA, August 2026 · gas $1.48/therm (EIA 2025 annual) (data as of 2026-10-25) ·
Output (heating capacity) on the furnace's data plate, not the input rating.
0.80 for older furnaces, 0.90–0.98 for condensing models.
Hours the burner is actually lit, not hours the heat is 'on'.
Difference per month (furnace − space heater)
The furnace heats the whole house for $108.83 a month more than one room on the space heater.
Estimate. Formula and sources are under “How it works”. Change any input; the result updates as you type.
2026 note: The federal 25C and 25D tax credits ended for installations after Dec 31, 2025. Our numbers use 2026 rules. State rebates, HEAR/HOMES programs and utility programs may still apply.
Formula
How it works
- Space heater per month = heater watts ÷ 1,000 × hours × 30 × electricity rate
- Furnace per month = furnace BTU/h ÷ 100,000 × gas price per therm ÷ AFUE × burner hours × 30
- Difference = furnace per month − space heater per month
One therm is 100,000 BTU. A furnace that delivers 80,000 BTU/h of heat burns 0.8 therm ÷ AFUE for every hour its burner is lit (0.89 therm at 90%): dividing by AFUE adds back the heat lost up the flue. If you only know the input rating, multiply it by the AFUE to get the output. The space heater's cost follows the usual watts × hours × rate. A space heater only pays off when it heats one room and the central thermostat is turned down, so the furnace actually runs fewer hours.
Sources: 1 therm = 100,000 BTU; residential natural-gas price by state (EIA, $/Mcf ÷ 10.37 to $/therm); electricity rate from EIA Electric Power Monthly table 5.6.A.
Worked example
A worked example
In Illinois, a 1,500 W space heater running 8 hours a day costs an estimated $69.55 a month at the state's electricity rate. A 100,000 BTU/h furnace at 80% AFUE with its burner lit 6 hours a day, at $1.08 a therm, costs $243.00 a month. The furnace heats the whole house for $173.45 more. That's the price of heating every room instead of one.
Reference
Reference table
Space heater vs furnace cost per month in US average (18.2¢/kWh, $1.48/therm)
| 60,000 BTU/h | 80,000 BTU/h | 100,000 BTU/h | 1,500 W heater · 6 h | |
|---|---|---|---|---|
| 2 burner h | $59.20 | $78.93 | $98.67 | $49.03 |
| 4 burner h | $118.40 | $157.87 | $197.33 | $49.03 |
| 6 burner h | $177.60 | $236.80 | $296.00 | $49.03 |
| 8 burner h | $236.80 | $315.73 | $394.67 | $49.03 |
Questions
FAQ
Is it cheaper to heat one room with a space heater?
Usually, if you turn the central heat down at the same time. At US average prices, a 1,500 W heater for 6 hours costs an estimated $49.03 a month, while an 80,000 BTU/h furnace at 90% AFUE with 4 burner hours a day costs $157.87. Heating several rooms with several space heaters loses that advantage quickly.
Is a space heater cheaper than a heat pump?
Usually not, for the same heat. A space heater turns 1 kWh into 1 kWh of heat. A heat pump moves heat from outside and delivers about 2.2 to 3.5 kWh of heat per kWh over a season, depending on the climate zone. The Mini Split calculator shows a heat pump's running cost in heat mode.
How low should I set the thermostat if I'm using a space heater?
Low enough that the furnace rarely runs while you're in the heated room, and never so low that pipes could freeze. Lower the "burner hours" input to see what fewer furnace hours are worth in your state.
Why is the difference so small in California?
Gas is expensive there ($2.12 a therm in our data) and so is electricity (29.8¢/kWh). A 1,500 W heater for 4 hours costs an estimated $53.55 a month against $80.34 for a 60,000 BTU/h furnace at 95% AFUE running 2 hours: a gap of $26.79.
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