Electric Radiator Running Cost Calculator
Estimate the cost of running a plug-in electric radiator, panel heater or oil-filled radiator. Add wattage, thermostat duty cycle, room hours, tariff and heating season to see daily and monthly cost.
Heater and Room Inputs
Estimated Heating Cost
Thermostat duty cycle is the key assumption. Measure with a plug-in meter if you need a tighter estimate.
This result turns a heater label into a room-use estimate. The duty cycle line matters because a thermostatic radiator that cycles can cost far less than the same heater running at full power.
What Drives Electric Radiator Cost
Wattage
A 2 kW heater uses 2 kWh if it runs at full power for one hour. That simple fact makes direct electric heat easy to cost.
Thermostat
Once the room reaches temperature, a thermostat may cycle the heater on and off. The duty cycle field estimates that average draw.
Room heat loss
Insulation, draughts, room size, outside temperature and door opening decide how often the heater has to run.
How to Use the Calculator
Enter the radiator wattage, then enter the hours you use it on a typical day. A 2 kW heater running for five hours at full power would use 10 kWh. In real rooms, a thermostat may reduce that if the room reaches the set temperature. Use 100% for a worst case, 50% to 70% for a heater cycling in a moderate room, and a lower value only if you have evidence from a meter or smart plug.
Enter days per week and the season length to plan monthly and winter costs. A heater used in a home office for five hours on weekdays has a very different annual cost from a bathroom heater used for 30 minutes after showers. If you use several heaters at the same time, enter the count or add their wattages together.
Electric radiators are nearly 100% efficient at turning electricity into heat in the room, but electricity can be expensive per kWh. Efficiency does not mean low cost. The cheapest option may be heating only the occupied room for a short time, but comfort, damp control and health needs matter too.
Formula and Method
average power in kW = radiator watts / 1000 x duty cycle x number of heaters
daily kWh = average power in kW x hours per day
daily cost = daily kWh x electricity unit rate
weekly cost = daily cost x days used per week
30-day cost = daily cost x 30
season cost = daily cost x season days used + included standing charge
full-power hourly cost = radiator kW x electricity unit rate x number of heaters
The standing charge is optional because most households pay it regardless of heater use. Include it only for a separate supply or a property-cost comparison.
Use Case Table
| Use case | Likely inputs | Cost pattern | Practical check |
|---|---|---|---|
| Home office boost | 1.5 to 2 kW, 3 to 6 hours, weekdays. | Moderate weekly cost if one room only. | Close doors and reduce draughts before raising the setting. |
| Bathroom warm-up | 1 to 2 kW, 0.5 to 1 hour. | Low per use, but can add up daily. | Use suitable bathroom-rated equipment only. |
| Whole flat direct electric heating | Several heaters, long hours. | High winter cost. | Review tariff, insulation, controls and heating system options. |
| Frost protection | Low thermostat setting, long period. | Depends on room heat loss and weather. | Use a thermostat and check pipes, damp and ventilation. |
Reducing Cost Without Losing Comfort
- Use the thermostat: Running at maximum after the room is warm wastes money.
- Heat the person and room together: Warm clothing, rugs and draught reduction can lower the heater setting.
- Use timers: Avoid heating an empty room by accident.
- Check plug safety: High-wattage heaters should not be run through weak extension leads or overloaded sockets.
- Control moisture: Very cold rooms can create condensation risk. Cost saving should not create damp or health problems.
Worked Example
A 2 kW electric radiator is used for five hours on five days each week. The room reaches temperature, so the duty cycle is estimated at 55%. Average power is 1.1 kW and daily use is 5.5 kWh. At 24.67p per kWh, that is about £1.36 per use day and about £6.78 per five-day week.
If the duty cycle is actually 100%, the daily cost almost doubles. A plug-in meter or smart plug reading can replace guesswork, especially in a room used all winter.
Room-by-Room Planning
Electric radiators are often used as top-up heat, so a single whole-house estimate can hide the useful detail. Cost a bathroom boost, a home office day and an evening living-room period separately. Each room has a different heat loss pattern, and each pattern calls for a different duty cycle. A small insulated room may reach temperature quickly, while a draughty room with solid walls may keep a heater close to full output.
Use the result to test changes before buying extra heaters. A timer may cut forgotten hours, a thermostat may stop overheating, and closing doors can reduce the heated volume. In some homes, improving curtains, draught-proofing or loft insulation may reduce the duty cycle more effectively than changing heater type. Do not reduce heating below a level that protects health, pipework and damp-prone rooms.
FAQ
Are oil-filled radiators cheaper than fan heaters?
At the same wattage and run time, the electricity cost is the same. Comfort, noise, heat distribution and thermostat behaviour can differ.
What duty cycle should I use?
Use 100% for worst case. Use a lower value only if the thermostat cycles or you have measured energy use.
Does the calculator include gas heating comparison?
No. It estimates electric radiator cost. Comparing heating systems needs boiler, heat pump or tariff detail.
Should I include more than one heater?
Yes if they run at the same time on the same pattern. If rooms have different use, calculate each room separately.
Can insulation change the result?
Yes. Better insulation, fewer draughts and closed doors can reduce the duty cycle, which is often the biggest uncertainty.
Sources
- Ofgem (2026) ‘Energy price cap unit rates and standing charges‘. Office of Gas and Electricity Markets.
- Energy Saving Trust (2026) ‘Heating your home‘. Energy Saving Trust.
- Electrical Safety First (2026) ‘Portable heater safety‘. Electrical Safety First.