A thermocouple‐type radiometer is constructed by mounting a blackened thin‐foil heat‐flux sensor on a reflective heat‐sink block. Either the sensor alone or the completed assembly is calibrated in a thermal conductivity apparatus. The device measures total hemispheric radiation and is estimated to be accurate to within 2%. Simplicity and ruggedness make the radiometer well suited for measuring output of radiant heaters in hostile factory environments.