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Heating system size calculator


How many kWh does my heater need to heat my room?

Standing in a shop and trying to find a heater specific for your home can be difficult. If the "size" of the heater is too strong, it would increase your energy bill unnecessary; if the "size" is too weak, you may need to stay in front of the heater to get the best benefit out of it. The "size" here means the heating system size of a heater, which is measured by Kilo Watt Hour (kWh). To find out the specific heater size for your room, we create a simple calculator here to help you out. All you need are a tape measure, a smart phone/calculator and our tool below.


  1. Measure the size of your room in square metres. (example 4 m long x 3 m wide = 12 m2)

  2. Measure the square meters of your windows and add them all up (1 m x 1 m = 1 m2)

  3. Measure the size of your external walls (the walls NOT facing another room) and subtract the square meters for the windows (2.4 m X 3 m -1 m2 = 7.2 m2 - 1 m2 = 6.2 m2)

  4. Type all results in the relevant green fields and select your location, insulation, build/ renovated time as well as your type of glazing and room height in meters (standard is 2.4 m)

  5. Your result will be the amount of kWh you require in a heater to heat your room up to 20 degrees Celsius (for international calculator please adjust to your temperatures appropriately; for example, if you get down to -3 degrees Celsius in winter, type in at the temperature 23)

Different climates, materials and living stiles require different products for best results. Get in touch for a free consultation- we help you find what works best for you according to science, not a marketing message.


Please be aware that this is a guide to give you an estimate value for your circumstances. For exact results your house would have to undergo expensive tests. As always, our calculators are based on public available data from official sources. The far- infrared heater calculator for international circumstances should also work for temperatures down to about -10 degrees Celsius.


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