Bulk density and dilatometer measurements were carried out for stoichiometric iron aluminide (FeAl) in order to determine the thermal vacancy concentrations as a function of time and temperature. For temperatures of 600 °C and below the specimen bulk density or length were found to depend on heat treatment history, i.e., they were not unique functions of the temperature. This path dependence suggests a lack of active sources and sinks for thermal vacancies in FeAl at temperatures below ≈600 °C.