Heat Loss Calculation and Radiator Selection

There are two main factors that will help you in specifying the right radiator:


  1. Desired room temperature
  2. The heat loss from the room.This depends on a wide range of factors such as the wall type (brick, insulated brick etc), number of exernal walls, what is above / below the room, window surface, window material etc.


The heat loss calculations can be complicated therefore we recommend that a heating engineer is consulted for precise calculation. However there is a practical method to calculate the heat loss and radiator size that is required. The heat loss from the room can be broadly calculated by measuring the space in cubic meters and then applying the following factors to the figure arrived at.

Lounges: 50
Bedrooms & Kitchens: 45
Common Areas: 40


“Heat loss = Room Volume (H x W x L) x Factor”

Room Height: 2,5 mt
Room Width: 5,0 mt
Room Length: 6,0 mt
Therefore Room Volume is: H (2,5mt) X W (5,0mt) X L (6,0mt) = 75m3

For a lounge that is 75m3 the heat loss can be calculated as follows:

75m3 x 50= 3,750 Watts (@Dt50C)

It may not be possible to choose a radiator that will exactly match the required heat therefore any radiator with the nearest output can be chosen. For large rooms two radiators may be required for better room comfort. The total output of the two radiators together needs to be equal to the required heat.