Air-source heat pumps are central to efforts to reduce building emissions. They use electricity to move heat out of the house in summer and into the house in winter. Over the course of a heating or cooling season, heat pumps can move three or more units of heat for every unit of electricity they consume. When combined with low-carbon electricity from wind and photovoltaics, they can deliver year-round comfort without fossil fuels.
Conventional heat pumps perform best under mild conditions. As outdoor temperatures drop, their efficiency—and the amount of heat they can deliver—falls off rapidly. Below a certain temperature, typically 30-40°F, they can no longer keep up with the house’s needs, and supplemental heat is required. The reliance on supplemental heat, particularly electric resistance, has given heat pumps a reputation as an expensive choice. Conventional heat pumps’ poor performance at lower temperatures has also limited their use in colder regions.
In the last two decades, a new generation of heat pumps suitable for colder climate zones has emerged. Many of these “cold-climate heat pumps” perform well at temperatures below 0°F. Their increased efficiency and the reduced need for supplemental heat make them a cost-effective alternative to electric baseboards, propane, and fuel oil. In some regions, they can achieve operating costs comparable to natural gas.
Unfortunately, public perception of heat pumps is influenced by the limitations of conventional equipment. To build confidence in the new technology, the Northeast Energy Efficiency Partnership (NEEP) and the EPA Energy Star program have established criteria for what constitutes a cold-climate heat pump. In this article, I’ll go over these criteria, then discuss features that allow cold-climate heat pumps to perform well at low temperatures.
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