A simple method for measuring thermal diffusivity is considered. It consists in suddenly heating one end of a sample and measuring the time it takes for a heat wave to arrive at the other end. This paper considers the application of this method for two kinds of boundary conditions relating to the heat input. These conditions correspond to step‐function heating (a) by radiation and (b) by a good contact to a constant‐temperature heat source, such as liquid metal.In addition to consideration of the effects on the analytic solution due to radiation heat loss, other factors which affect the accuracy and sensitivity of the technique are discussed. The heat‐wave method is related to many other techniques for measuring thermal diffusivity, ranging from Angstrom's original method to several pulse heating techniques which have been described recently. The interrelationships between these different techniques are discussed.