This paper presents a theoretical and experimental comparison between the performance of isobutane (R600a) and n-butane (R600) for a built-in household refrigerator. Energy consumption tests were performed at two ambient temperatures (16°C and 32°C) and two thermostat positions (hot and cold). Second law efficiency was used to evaluate the performance inventory for both fluids under different system configurations. Results have shown an overall energy consumption saving up to 14% when a system originally designed to run on isobutane is optimized to run on n-butane. It was observed that due to its lower volumic refrigerant effect, the application of n-butane is beneficial for low thermal load systems such as small household refrigerators required to comply with new energy consumption policies.