DIY Doctor UK DIY Forums

Can any one please tell me how the sizing of radiator output is measured? Is there a standard temperature differential between water input temperature and room temperature that is used to give a normalised heat output? How else do you measure the amount of heat a radiator will put out? Anyone out there know the answers?

A radiator size for a room is calculated by performing a heat loss calculation. Each component that makes up that room, such as brick walls, plaster ceilings, timber floors, glass, wooden doors lose heat at differing rates i.e. there thermal conductivness expressed as a U value (w/m2) The area of each component is multiplied by the U value and the figres added together and mulitplied by the number of times you would expect the air volume to change every hour with in that room. Multiply that by the temp. differential, that is the anticipated worst average external temperature in the UK -1 deg C or -3 deg C depending what area of the UK you are in, and the required internal temperature required . This gives a total Watts output required to heat that room to cope with those conditions.