Radiators are often not correctly sized for the room size or intended use. It is important to correctly size radiators for the size of room to be heated and environmental conditions. Rooms with large windows, north facing [in northern hemisphere] and south facing [in southern hemisphere] take more energy to maintain at a comfortable temperature. Radiator sizing also needs to take account of ceiling height. As heat rises a larger radiator size is needed for higher ceilings.
Always check manufacturers data for heat output, stated in BTU/Watt values. Note bathroom towel rail type radiators are generally not suitable to heat a bathroom. Be sure to calculate room heating requirements when choosing a towel radiator.
The table below details the correct values for different types of rooms and locations. The values are based on 1m³. You can multiply the table values by the volume of your room [length x width x height] to see what you need. Manufacturers and Retailers can give details of Watts/BTU values for each radiator size and type.
|Per m³||lounge, sitting room, study, games room, dressing room, dining room||bedrooms, bathrooms and shower rooms||common areas, halls, landings and kitchens|
|Approximate heat loss value||Approximate heat loss value||Approximate heat loss value|
|standard room, where non of the factors below apply||51||174||41||140||31||106|
|north facing room||59||200||47||161||36||122|
|very large windows or french windows||61||209||49||168||37||127|
|very large double glazed or french windows||56||191||45||154||34||116|
|north facing with double glazing||54||183||43||147||33||111|
|north facing* with large windows or french windows||69||235||55||189||42||143|
|north facing room with very large double glazed windows or french windows||64||218||51||175||39||132|
* North facing in northern hemisphere and south facing in southern hemisphere. This is because the exterior structure of the building is in permanent shade. This could also apply to buildings in close proximity to each other. It may also be the case that exterior walls are in permanent shade.
When adding a new radiator to an existing system it is important to check the radiator sizes of all existing radiators. The heat output capacity of your boiler needs to be checked to confirm the additional radiator[s] will work efficiently.