A study was made of an automatic- and a manual-defrost refrigerator/freezer combination, andan upright and a chest freezer to measure the effect on energy consumption of five variableusage conditions: thermostat setting, ambient temperature, food load, door-opening frequency,and relative humidity. No evaluation was made of the effect of frost build-up.Ambient temperature and thermostat settings were found to have considerably greater effect onenergy consumption than door-opening and relative humidity changes for the specimens tested.