The thermoelectric Peltier device is positioned in a heat transfer path, between two copper blocks. It extracts heat from one block (cold reservoir) and transfers it to the other block (hotreservoir). In order to measure the heat transfer rate, the cold reservoir is fitted with an electric heater. By varying the electric power into the system,the behaviour of the system at different operating points and temperatures can be established. The heat extracted is transferred to the hot reservoir,together with heat generated by the electrical supply to the Peltier device.This heat is removed by a water cooled heat exchanger. The flow rates can be adjusted to provide a range of operating temperatures. The Peltier device can also be used to generate a small quantity of electric power when a temperature difference is applied. Instrumentation is provided to measure the temperatures of the blocks, the electric power supplied to the Peltier device, the cooling water flow rate and the cooling water temperature rise. The heater power is measured by the, and so it is possible to establish a complete energy balance for the system.