Abstract: A calorimeter for measuring the quantity of heat flowing through a solid surface, comprises a heat insulated chamber having a recess of predetermined volume, to be placed against the surface whose heat flow is to be measured. Within the recess is a thermometer. The thermometer measures the initial temperature of the recess when the device is applied to the surface whose heat flow is to be measured, and also the final temperature of the recess after a predetermined period of time. Having regard for the temperature change during the elapsed time, and the volume of the chamber, the heat flow through the surface to which the device is applied can be calculated and displayed.