Heat Output Calculator

For radiators to be able to heat your home, they need to pass their warmth to the air in the room. The efficiency of their "heat loss" is measured in BTUs (British Thermal Units) or Watts (1 BTU is approximately 0.3 Watts).

Factors such as the radiator size, design and material it is contructed from will govern the BTU/Watt heat output - larger radiators have more surface area to lose their heat to the room. Aluminium radiators are light in comparison to steel or cast iron but give off their heat more efficiently too and so will have a greater BTU output than a similarly sized steel or cast iron radiator.

The heat your room requires will depend on the room dimensions, windows/exterior doors and the wall/ceiling types.

How do I calculate the BTUs needed for my room?

Our BTU Calculator is an accurate guide as to what level of BTU and Watt output will efficiently heat your room. Please note: the calculated figure is for the combined heat output of all radiators and/or towel rails in your room (larger rooms may require more than one).

What dimensions does my radiator need to be?

This depends on the design of the radiator you choose. For larger rooms, it might be better to opt for two (or more) radiators which can distribute heat more evenly, with any calculated heat requirements split accordingly.

We always recommend the use of thermostatic radiator valves where possible as they allow individual adjustments to heat outputs from each radiator. Even if the radiator is a little over-sized for a room, the thermostatic radiator valves (TRVs) will keep your temperatures controlled whilst also allowing for additional performance during cold spells.

For the best advice, a suitably qualified heating engineer is recommended.