The answer to how many BTU to heat a room will depend on which room and its features. As mentioned above, everything from the types of windows the rooms have, if any, to the amount of insulation and room size will have an impact on this. As a guide, 1 watt of energy is equivalent to 3.41 BTUs. The simplest way to work out how many BTU your room needs to be heated efficiently is to use our BTU calculator which will ask you step-by-step details about the room and will then recommend which radiators you need.