Space Heater Electricity Cost Calculator
Enter your appliance data and electricity tariff to calculate energy use and cost. Example inputs are editable.
Enter your values and select Calculate.
Enter actual heating on-time. A thermostat may switch heating off during a longer elapsed period. Excludes off-cycle consumption. Energy charges only; fixed fees and taxes are excluded unless included in your rate. Use one currency consistently. Decimal point or comma accepted; no thousands separators.
Calculation formula
Daily kWh = input watts × accumulated heating hours / 1000. Period energy = daily energy × days. Period cost = period energy × price per kWh.
Check your heater's selected heat setting: the model and setting determine its rated power. For example, Lasko lists 900–1,500 W and 120 V for its model 6435. At a constant 1,500 W, one hour uses 1.5 kWh and costs $0.30 at an assumed $0.20/kWh.
Calculate your electricity cost with your own watts, hours and tariff.
Heat setting and thermostat time are different inputs
A lower heat setting can reduce the power drawn while heating. A thermostat can also reduce total heating time by switching the heater off when the selected temperature is reached. Do not confuse eight hours with the heater available to operate and eight hours of uninterrupted full-power heating. Record the setting and accumulated on-time, or measure energy directly.
An eight-hour period with half the time heating
For a simplified 1,500 W heater that heats for four hours during an eight-hour period, heating energy is 1.5 × 4 = 6 kWh. At $0.20/kWh that is $1.20. Continuous heating for all eight hours would be 12 kWh and $2.40. This comparison excludes any separate off-cycle consumption and assumes the same full-power draw whenever heating is active.
Six examples of power, time and electricity cost
Illustrative constant-power heating periods. Ratings other than the documented Lasko settings are example inputs, not a product survey. The $0.20/kWh tariff is illustrative, not a quoted local rate. Calculations use unrounded inputs; displayed results are rounded.
| Input power | Operating time | Energy | Cost at $0.20/kWh |
|---|---|---|---|
| 750 W | 1 hours | 0.750 kWh | $0.150 |
| 900 W | 2 hours | 1.800 kWh | $0.360 |
| 1500 W | 1 hours | 1.500 kWh | $0.300 |
| 1500 W | 4 hours | 6.000 kWh | $1.200 |
| 1500 W | 6 hours | 9.000 kWh | $1.800 |
| 1500 W | 8 hours | 12.000 kWh | $2.400 |
Energy (kWh) = average electrical input watts × hours ÷ 1,000. Multiply energy by the actual price per kWh for the energy charge. Include other billing components separately. The watts to kWh calculator handles another duration.
Compare equal comfort and equal periods
A lower-wattage heater may run longer to supply the desired heat. To compare operating costs fairly, record energy over equivalent occupied periods and note the room conditions. The calculation cannot tell whether the heater is adequate for a room. Use the heater exactly as its manual directs; a wattage calculation does not approve the outlet, extension arrangement or unattended operation.
Use the right inputs in the electricity-cost calculator
Enter one device or add it to a household inventory. When watts already represent the average over your entered hours, use a 100% duty factor. When watts represent an on-state value, use accumulated on-time or an appropriate duty factor, but do not apply both reductions. Keep product ratings, measured results and assumptions distinguishable in your comparison.
Frequently asked questions
Does a 1,500 W heater use 1.5 kWh every hour?
Only if it draws that power continuously for the whole hour.
Does choosing a lower thermostat temperature change its watt rating?
It can change the time spent heating. The selected heat mode and appliance design determine the on-state rating.
Are all small heaters 1,500 W?
No. Check the specific appliance; size and appearance do not establish electrical input.
Technical source
Lasko's model 6435 specification lists 900–1,500 W output, 120 V and a thermostat. These specifications apply to that model. This calculator's worked scenarios are calculations, not measurements performed on products.
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