Can running an air conditioner in reverse save the planet?

It’s necessary but not sufficient. We also need to weatherize homes and clean the grid.

Stabilizing Earth’s temperature requires that humans add no net greenhouse gasses to the atmosphere. Keeping the increase in temperature relative to pre-industrial times to below 1.5°C requires that we get to net-zero emissions before mid-century. To achieve this, we must stop burning fossil fuels like natural gas to heat our buildings and switch to efficient electric heating solutions such as heat pumps.

Electric heat pumps—air conditioners running in reverse—are a mature technology that can use electricity to efficiently heat homes. However, deploying them effectively for people and the planet also requires rapid progress on two complementary fronts. First, we must shift the electric grid to net-zero generation sources. Second, we must improve America’s housing stock, making homes more energy-efficient.

Currently, only about one in 10 U.S. households use heat pumps. Our recent analysis shows that about a third of single-family households would save money by switching to heat pumps from whatever heating technology they currently use. Heat pumps are most likely to save people money if they live in mild climates, if they currently use resistive heating, and if their houses are large and old. In new homes, even in Boston and Minneapolis’s cold climates, installing a heat pump — which works as an air conditioner in the summer and a heater in the winter — might be cheaper than installing a furnace and an air conditioner separately.

In much of the Midwest and parts of the East Coast, switching from natural gas to heat pumps would raise people’s heating bills. This is because heat pumps that extract heat from the ambient air get less efficient as that air gets colder and because in most parts of the country, electricity is more expensive than natural gas. Heat pumps are also often more expensive to install than natural gas furnaces.

Higher heating bills hurt low-income households, who already spend a disproportionate share of their money on energy. Thirteen million homes reported leaving their homes below the 64°F considered healthy. American families sometimes have to choose between enough warmth or enough to eat. Policymakers can help low-income households become more efficient to lower their bills. The federal government’s Weatherization Assistance Program was set up to do just that. Expanding it, as the Energy Act of 2020 seeks to do, will strike a blow for energy justice and the climate.

Another barrier to heat pump adoption is that homeowners are not aware of their benefits. The DOE’s Home Energy Score initiative should help people account for energy use in their home buying and renting decisions and drive them to more efficient homes.

Whether electrification of heating produces a benefit to the environment and for human health depends on the electricity grid. We found that a shift to an air source heat pump from natural gas would increase CO₂ emissions from heating a typical single-family home in large parts of the east coast and mid-Atlantic, the Midwest, and even parts of the West. Even in parts of the country where switching from natural gas to heat pumps would cut CO₂ emissions, the change increases damages from the emissions of so-called criteria pollutants, including sulfur dioxide (SO₂), oxides of nitrogen (NO_x), and fine particulate matter (PM_2.5). This increase is large enough to overwhelm the benefit from reduced CO₂ emissions if those emissions are valued at $40 per ton of CO₂ avoided. But, if the grid were rapidly decarbonized, a heat pump installed in the next few years in any part of the country would over its lifetime reduce health and environmental harms.

Heat pump adoption is a valuable tool for decarbonizing residential energy consumption. It would save money for 1/3 of single-family homeowners today. The Department of Energy is developing programs to help homeowners realize this opportunity. However, heat pumps are not a panacea, as progress in electrification is entangled with progress in decarbonizing electricity. To make electrification work in a way that does not exacerbate already-glaring inequities, we need to rapidly clean up the electric grid and make the U.S. housing stock much more efficient.

Parth Vaishnav is an Assistant Professor of Sustainable Systems in Climate + Energy at the University of Michigan.

Thomas Deetjen is a Research Associate at the University of Texas Center for Electromechanics.

Photo by Michael Tuszynski from Pexels