Source of the difference: COP
All resistance heaters are physically equally efficient: an oil-filled radiator drawing 2 kW and a fan heater drawing 2 kW both give the room 2 kW of heat. There is no such thing as a 'low-consumption heater'; there is only a heater with lower power that gives less heat. An air conditioner, on the other hand, is a heat pump: it moves the heat in the outdoor air inside. An air conditioner with a COP of 3 gives about 3 kWh of heat for 1 kWh of electricity.
| Device | Heat delivered per 1 kWh of electricity | When does it make sense? |
|---|---|---|
| Oil-filled radiator | About 1 kWh | Short-term, backup heating; quiet and slow |
| Fan heater / electric stove | About 1 kWh | Short periods in a small space like a bathroom |
| Infrared heater | About 1 kWh | Outdoors or spot heating of a single person |
| Inverter air conditioner (mild weather) | About 3-4 kWh | Rooms used continuously |
| Inverter air conditioner (below freezing) | About 1.5-2.5 kWh | Still more efficient than a heater; capacity drops |
The values show the general trend; the exact value depends on the unit's model and the SCOP value on its label.
A simple calculation for your own bill
Multiply the heater's power (kW) by hours of use: a 2 kW heater running 5 hours a day uses 10 kWh. An air conditioner with a SCOP of 3 delivers the same heat with about 3.3 kWh. The difference multiplied by your electricity unit price shows the monthly saving. To do the calculation per device, you can use our energy cost calculator.
Safety if you use a heater
- Do not plug high-power heaters into extension cords or multi-socket strips; the capacity of the socket and the line can be exceeded.
- Keep them away from curtains, furniture, and laundry.
- Choose a model with tip-over protection and overheat protection.
- Do not run more than one heater on the same line; a fuse that trips often is a warning.
Decision: which one in which situation?
For a living room, study, or shop that is heated more than a few hours a day, an air conditioner is far more economical; if you have an air conditioner at home, using it instead of a heater often lowers the bill noticeably. If you have no air conditioner and only need short extra heat in winter, a small heater may be enough. For a permanent solution, an inverter air conditioner suited to the room size: how many BTU air conditioner should I buy.
Air conditioner installation for winter heating
Write your room size and how you use it; we will determine the right capacity and prepare an installation quote.
You can find the right settings for heating with an air conditioner in our guide to heating with an air conditioner, and a comparison with natural gas in our article is heating with an air conditioner cheaper than natural gas.
Frequently asked questions
Which uses less electricity, an oil-filled radiator or an air conditioner?
For the same heat, an inverter air conditioner uses about one third of the electricity of an oil-filled radiator in mild weather.
Is an infrared heater economical?
An infrared heater also converts electricity to heat one to one. Its advantage is that it heats the person in front of it, not the air; it is not more efficient than an air conditioner at heating a whole room.
Can an air conditioner cost more than a heater?
Almost never in continuous use. Even though an air conditioner's efficiency drops in very cold weather, it is generally still higher than a resistance heater.
What do you recommend for the bathroom?
For short-term use, a bathroom-rated heater with suitable safety features may be enough; pay attention to its suitability for damp environments.