google -> Watt Heathttp://en.wikipedia.org/ (...)
"As a form of energy heat has the unit joule (J) in the International System of Units (SI). However, in many applied fields in engineering the British Thermal Unit (BTU) and the calorie are often used. The standard unit for the rate of heat transferred is the watt (W), defined as joules per second."
Det er et spørgsmål om hvor meget varme den kan flytte.