Hong Life CalculatorsUnderstanding the space heater running cost calculator — concept and principle
Portable electric heaters are cheap to buy but can be expensive to run, because they turn electricity directly into heat at a high wattage. This calculator estimates monthly energy use and monthly and yearly cost from the heater's power, daily running hours and your electricity price, so you can compare it with central heating or decide how many hours of use you can afford.
How it is calculated
- kWh per month = W ÷ 1000 × hours per day × days per month
- Monthly cost = kWh per month × price per kWh
- Yearly cost = monthly cost × 12
Use the setting you actually run (many heaters have low and high settings) and the hours the element is really on. Days per month lets you model only the cold season.
The principle
Energy is power × time; a 2,000 W heater on for one hour uses 2 kWh. Every resistive heater, whether fan heater, oil-filled radiator, convector or infrared panel, converts electrical energy into heat with essentially 100% efficiency, so 1 kWh of electricity always gives about 1 kWh of heat. No resistive model is "more efficient" than another in that sense; they differ only in how quickly and where the heat is delivered. A heat pump is different: it moves heat from outside, typically delivering two to four units of heat per unit of electricity. A thermostat saves money by switching the element off once the room is warm, so real hours at full power are often lower than the hours switched on.
Worked example
- Inputs: 2,000 W, 5 hours per day, 30 days, $0.25 per kWh.
- Power in kW: 2,000 ÷ 1,000 = 2 kW.
- Monthly energy: 2 × 5 × 30 = 300 kWh.
- Monthly cost: 300 × $0.25 = $75.00.
- Yearly cost: $75.00 × 12 = $900.00.
| Power (W) | Monthly cost |
|---|---|
| 500 | $18.75 |
| 1,000 | $37.50 |
| 1,500 | $56.25 |
| 2,000 | $75.00 |
| 2,500 | $93.75 |
| 3,000 | $112.50 |
| 4,000 | $150.00 |
How to read the result
The yearly figure assumes twelve months of identical use, so for a winter-only heater count only the heating months. Heating one small room for a few hours can be cheaper than running whole-house heating, but heating several rooms this way usually costs more than gas or a heat pump. Use the heating fuel comparison calculator to compare the cost per kWh of heat.
Common mistakes
- Believing claims that one resistive heater produces more heat per kWh than another.
- Using the full running time when a thermostat cycles the element.
- Counting twelve months for a seasonal appliance.
Frequently asked questions
Are oil-filled radiators cheaper to run than fan heaters?
Per kWh, no; both turn electricity into the same amount of heat. Oil-filled units release heat more slowly and evenly after switching off.
How much does a space heater cost per hour?
Its kW times your price: 2 kW × $0.25 = $0.50 per hour at full power.
Is a space heater cheaper than central heating?
Only when you heat a small area for a short time. For the whole home, gas or a heat pump is usually cheaper per unit of heat.
Sources: U.S. Department of Energy, Energy Saver — portable heaters · U.S. Consumer Product Safety Commission — space heater safety