To compute the heat loss, we need to sum heat loss through all the surfaces of the room and take into account different characteristics of the materials used in the construction. The total heat loss is a sum of losses through walls, floor, and ceiling.

To use the heat loss calculator and to find the power of the heater you need to give the dimensions of your room, specify on which floor it is and what type of insulation the walls have. If you are unsure which insulation type to choose, go for the worse insulation. It’s safer to be pessimistic.

Finally, you should also specify how many external walls are there. In the advanced mode, you can also include the number of windows and doors.

With this information, we can compute the heat loss ( in watts divided by the temperature difference).

The last bit of the information needed is the difference of temperatures between inside (internal temperature) and outside (ambient temperature). The internal temperature depends on your comfort. The ambient temperature should be the minimum temperature occurring in your region-for Bulgaria it’s usually -15oC.

Knowing the heat loss, we can estimate the power of a heater/radiator in Watts.

Then you can select the radiator with the closest power from the “Heat output” drop-down menu.