Air source heat pumps work in most of the United States; however, they are not cost-effective in areas with extended periods of sub-freezing temperatures, according to the U.S. Department of Energy. As of 2015, manufacturers are working on technology to make them cost effective for all climates.
Heat pumps are the most efficient electric heat sources in moderate climates, reports the U.S. Department of Energy. They produce three times as much heat as an electric furnace using the same amount of energy. However, at lower temperatures, they become less effective. At these temperatures, because the heat pump is unable to supply enough heat to keep the house warm, it activates the backup heating source, usually a set of resistance coils. Forced-air electrical resistance heating is one of the least effective and most expensive ways to heat a home.
While the cold-climate heat pump is not yet available to consumers, it uses a two-speed fan and two compressors to remain efficient to 15 degrees Fahrenheit. A plate heat exchanger makes it effective at temperatures below zero.
The all-climate heat pump features a design that allows it to remain efficient at low temperatures without using an alternative heat source. While the initial investment is high, the unit could reduce costs for heating and cooling by 25 to 60 percent.