Refrigerator-freezers energy consumption is greatly affected by room temperature, door opening and thermostat setting position. Two frost free household refrigerator freezers of the same capacity were tested in the laboratory to determine the sensitivity of their energy consumption to various usage conditions. The experiments were conducted to investigate the effect of single variables, such as temperature, thermostat setting positions and door opening, and their combined effect on energy consumption. Our investigation reveals that room temperature has the higher effect on energy consumption, followed by door opening. Thermostat setting position has the lower effect on energy consumption. More detailed tests were performed under different room temperature, thermostat setting position arid door opening conditions. With the experimental results, a first order mathematical model has been developed to investigate their combined effect on energy consumption. The test results are discussed and presented.