All worked examples below use explicitly chosen inputs. They are not measured household averages, utility quotes, or guaranteed savings.
Hourly and monthly costs at three example rates
Convert watts to kilowatts before multiplying by hours and price. A 1,500-watt setting draws 1.5 kW while operating at that power. The table assumes continuous full-power operation during the stated hours. The rates are scenarios, not current prices for particular states or utilities.
| Example rate | One hour | 4 hours/day | 8 hours/day |
|---|---|---|---|
| 10¢/kWh | $0.15 | $18.00 | $36.00 |
| 20¢/kWh | $0.30 | $36.00 | $72.00 |
| 30¢/kWh | $0.45 | $54.00 | $108.00 |
Reference: EIA: Measuring electricity
A thermostat changes runtime, not the price of each kWh
Being switched on for four hours does not necessarily mean heating at 1,500 watts for four hours. A thermostat may stop the heating element once the room reaches its setpoint. If it heats for half of a four-hour period, the simplified estimate is two full-power hours.
At 20¢/kWh, four scheduled hours at 50% active time cost $18 over 30 days, compared with $36 at 100%. The 50% assumption is a scenario, not a typical value. Room heat loss, weather, thermostat settings, and the heater affect cycling. Fans and controls can use electricity when the element is off, which this simplified cycling calculation does not separately model.
Does a 750-watt setting cut the cost in half?
For the same operating time, yes: half the input power uses half the energy. But it also supplies less heat during that time. If a 750-watt setting needs eight hours to do a job that a 1,500-watt setting does in four, both use 6 kWh.
Do not compare heaters using the wattage alone. Compare the energy used while delivering the comfort you actually need. Two electric resistance heaters with the same measured input power and runtime have the same electricity cost in this model, even if their purchase prices or marketing claims differ. This comparison does not extend to heat pumps, which use a different heating process.
Turn a daily change into a seasonal budget
Suppose you reduce full-power heating from four to three hours each day. At 1,500 watts and 20¢/kWh, that saves $0.30 per day, or $9 over a 30-day month. Over four such heating months, the arithmetic saving is $36. It assumes the removed hour is not replaced by another heater or additional central heating.
A space heater may reduce total spending if targeted heating lets you reduce a more expensive whole-home load. It may also simply add another load. Compare the change in your overall energy use, including gas if applicable. Do not assume a room heater automatically makes the household bill lower.
Our calculator’s annual result repeats the chosen monthly schedule 12 times. For a winter-only budget, use the monthly estimate times the number of months you expect to heat. Label that as a seasonal scenario rather than a measured annual cost.
A cost example is not a recommendation to run it unattended
The eight-hour column is a calculation scenario, not advice to run a portable heater while sleeping. CPSC advises turning space heaters off before sleeping or leaving the room, keeping them at least three feet from combustible materials, and plugging them directly into a wall outlet rather than a power strip or extension cord. Follow the heater’s instructions and safety guidance.
Reference: CPSC: Space heater safety recommendations
Sources & calculation notes
References checked 2026-10-08. Example arithmetic is calculated by HomeWattCheck. Article review dates are separate from the EIA data period displayed in our calculators.
Each calculator states its scope beside the result. Appliance tools estimate electricity at one rate; the time-of-use comparator includes two price periods and entered fixed fees. Complex tariffs may need additional calculations. State averages describe reported residential revenue per kWh, not your utility’s offer. See our data sources and methodology or state rate comparison.