Abstract: A heat meter comprises a transducer (6) for measuring the rate of flow of water through a conduit (58) and a transducer (10) for measuring the temperature difference between two spaced locations (90, 92) of the conduit (58). The output of the flow rate transducer (6) is supplied as an input to the temperature difference measurement transducer (10) and the output of the temperature difference measurement transducer (10) is supplied to a digital display unit (14) to display the amount of thermal power exchanged with the water between the two spaced locations.