The system requires electricity to operate the loop pump, the compressor and the circulating fan (in forced air distribution). It also uses electricity in the backup mode to deliver sufficient heat on very cold days, and requires power throughout the year to operate the water heating component. The amount of power used will depend on the size of the unit, operating times and sizing considerations, but an average residential unit would require 11,000 kWh per year, which represents an annual cost of $935 (based on 2001 retail prices).