Space Heater vs Furnace Calculator
| Electric rate ↓ · monthly bill → (gas $1.50/therm, 95% AFUE) | $80 bill | $120 | $160 | $200 |
|---|---|---|---|---|
| 10¢ per kWh | Furnace | Zone wins | Zone wins | Zone wins |
| 15¢ per kWh | Furnace | Furnace | Zone wins | Zone wins |
| 20¢ per kWh | Furnace | Furnace | Furnace | Zone wins |
| 25¢ per kWh | Furnace | Furnace | Furnace | Furnace |
Enter your electric rate, gas rate, furnace efficiency and what the whole house costs to heat in a winter month. The calculator prices an 8-hour evening both ways: one 1,500 W heater holding the room you are in, against the furnace carrying the house.
Per unit of heat the gas furnace wins at almost every American rate pair - a space heater is resistance heat, the most expensive heat there is. Zone heating can still win the evening, because you are not replacing the furnace, only keeping it off while one sealed room is occupied. The catch is brutal: if the thermostat never drops, you are paying twice for the same warm air.
How to use
- Both rates come off the utility bill - cents per kWh for the heater, dollars per therm for gas.
- The furnace AFUE is on the yellow sticker: 80 is an aging unit, 95 is modern.
- Use a real winter month for the whole-house bill, not a shoulder-season one. The verdict updates live and remembers your numbers.
Frequently asked questions
Is it cheaper to run a space heater than the furnace?
Only when the heater evening - 12 kWh at your rate, $2.04 at 17 cents - costs less than your share of the furnace evening, roughly a third of one day of the monthly bill. Zone heating wins on high bills and cheap electricity; the calculator runs your exact pair.
How much does a 1,500 watt space heater cost per hour?
Rate times 1.5: 17-cent power is about 26 cents an hour, 30-cent power is 45. An evening of it can out-cost many whole-house furnace evenings, because resistance heat is priced per BTU at roughly triple gas.
Can a space heater heat a whole house?
No: about 5,100 BTU per hour against a furnace pushing 40,000 to 80,000. It holds one closed room. Whole-house comfort from plug-in heaters means a dozen of them on circuits that were never wired for the job.
Do I save money if the space heater and furnace both run?
Never. The heater only saves money as a substitute - the furnace stays off, or the thermostat drops several degrees while the heater carries the occupied room. Both running at once is double-priced heat for the same air.
What about an all-electric home?
Then the heater and the furnace are the same resistance heat per BTU, and zone heating wins on area alone: warming 200 square feet instead of 2,000. That is the one case where the space heater is strictly the same machine with a smaller scope.