Heat meters measure the quantities of heat consumed in an installation (e.g., a hot water type heating system). They consist essentially either of a liquid supply meter, two thermometers placed respectively at the intake and outlet of the conduit, and a counting and totalising mechanism. This group also covers thermocouple heat meters. Small heat meters of the types mounted on radiators in blocks of flats so that central heating costs can be fairly divided resemble thermometers and contain a liquid which evaporates under the effect of heat.