Calculate Power of a Heating

How powerful does the heating need to be for which room? Here you can calculate the output of a radiator in watts (W) from the room size and insulation. The basic value is the performance per m², it depends on the insulation. 80 is used for well-insulated buildings and 150 for poorly insulated buildings. 100 is a good reference value for new buildings. A Central European climate and a desired room temperature of 20° C are assumed. Other factors that can play a role are room layout, ceiling height, type and number of joints and others that are not considered here.

Instead of one radiator, the power can also be distributed over more than one. This calculator is used to roughly estimate the required heating capacity. Contact a specialist company before installation or replacement. The recommended power is higher than the minimum power because more powerful radiators are more efficient.


Type of room: Bathroom   with sloping roof  
Basic value: W/m²
Room size:
Minimum power of the radiator : W
Recommended power of the radiator : W

Please enter room size, minimum power or recommended power, the other values will be calculated.

Minimum power = basic value * room size
Recommended power = minimum power * 1.4
10% more for bathrooms, 20% less for sloping roof.
1 kilowatt (KW) = 1000 watts (W)
m² = square meters

Thermal image radiator
Thermal image of a radiator, photography in infrared.

Here you can convert metric units into customary and imperial units and convert temperature units.

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