Heat pumps efficient, getting even better

As society looks to use less petroleum for heating, heat pumps represent an alternative that can use electricity to provide space heating and cooling. U.S. efficiency standards for heat pumps are set to tighten in 2023 -- but in many cases, the heat pumps sold today already meet those future standards.

Heat pumps can provide heat while avoiding direct combustion and carbon emissions, and can be powered by electricity from renewable resources. Heat pumps can also be cost-effective and efficient. According to the Maine Department of Environmental Protection, Maine's residential sector is responsible for 18% of the state's total greenhouse gas emissions, primarily resulting from space heating. Heat pumps offer a significant opportunity for "beneficial electrification" -- using electricity generated by lower-carbon resources to displace the direct combustion of higher-carbon fossil fuels. Nationally, according to federal data, about 13 million homes (11% of the total) use heat pumps for heating or cooling, and many states are increasing incentives for heat pump installation.

Heat pumps sold in the U.S. are subject to federal efficiency standards. Under the Energy Policy and Conservation Act of 1975, the U.S. Department of Energy has the authority to develop and implement minimum energy conservation standards for appliances and equipment , and to revise the standards if the amendments are energy-saving, technologically feasible, and economically justifiable. The subsequent National Appliance Energy Conservation Act of 1987 set minimum efficiency requirements for central air-conditioning and heat pump equipment sold in the United States. The first round of efficiency standards under that law took effect in 1992, with amendments in 2006 and 2015.

Heat pump efficiency can be measured by a metric called heating seasonal performance factor or HSPF. HSPF represents the ratio of heat output over the heating season to watt-hours of electricity used; higher numbers mean the consumer got more heat for less electricity. Under the currently effective standards set in 2015, air-source heat pumps sold in the U.S. must have a HSPF of at least 8.2. But under a 2017 Department of Energy rulemaking, beginning in 2023, the minimum HSPF will increase to 8.8.

While the tightened standard may affect some models with marginal efficiency, many heat pumps sold today already outperform the 2023 standard, as do most incentivized by state and utility programs. For example, Efficiency Maine Trust's rebate program for ductless heat pumps provides incentives for installations with a minimum HSPF of 12.0 for systems with one indoor unit or 10.0 for systems with more than one indoor unit. Because these incentivized units all exceed the future federal standard, their sales should not be affected by the 2023 standard. If nothing else, the tightening performance standards suggest that heat pumps will continue to play an increasing role in space heating and cooling over the coming years.