Bottom-freezer refrigerator designs are usually less efficient than top-freezer refrigerators of a similar size. However, several models of bottom-freezer refrigerators are certified as energy-efficient appliances by the Energy Star program of the U.S. Department of Energy.
Most modern refrigerator designs place the compressor for the refrigerator in the base of the appliance. Because of this, waste heat from the compressor is located much closer to the freezer in bottom-freezer designs, forcing the refrigerator to use more energy to keep the freezer cold as compared to a top-freezer model.
For example, the most energy-efficient bottom-freezer refrigerator with an Energy Star rating as of 2015 uses 337 kilowatt-hours of energy per year, while a comparable top-freezer refrigerator uses 336 kilowatt-hours of electricity and has an additional 1.5 cubic feet of capacity.