You can heat a building in many ways. A boiler heats water and cycles it through radiators that heat rooms. A furnace transfers heat to air, which it then pushes through vents into living spaces.
Most American homes run these devices by burning fossil fuels. Depending on your geographic location and the age of your home and its systems, those fuels might include distillate fuel oil (mostly still used in the Northeast), propane (common in rural areas), or natural gas (common everywhere else). Every one of these releases carbon dioxide into the atmosphere when burned.
But boilers and furnaces aren’t your only options. Instead of heating the air, heat pumps move heat from one place to another by converting a substance called refrigerant between its liquid and gas forms. Your refrigerator is a heat pump. So is an air conditioner. Both of those devices pump heat in reverse: Warm air is absorbed by the refrigerant coils and pumped out. Your fridge and AC unit move heat in only one direction. But a heat pump can do both, meaning that the same appliance can heat in the winter—even in very cold climates—and cool in the summer. (“Heat pump” is a terrible, confusing name for these gadgets.)
Heat pumps have been around for decades, but they didn’t used to be very efficient, especially in extremely cold weather. That’s changing. Now some cold-climate heat pumps can transfer heat effectively in subzero temperatures. An oil- or gas-fueled furnace (or other backup heat sources) might be required on the coldest days, but on all the others, your heat can be electric.
In Maine, the lack of natural-gas infrastructure made it easy for the state to encourage electrification of home heating. Central air is uncommon in the state, and installing a heat pump adds cool air-conditioning for free. Maine’s electricity grid is already very clean, and these new heat-pump devices are much more efficient than window AC units.
Michael Stoddard, the executive director of the Efficiency Maine Trust, the state’s energy-efficiency organization, told me that more than 60,000 heat pumps have been sold to Mainers in the past seven years. Some Mainers have been burned by the high cost of heating oil, a commodity whose price fluctuates. State-sponsored consumer-rebate programs, including one that offers up to $1,500 back on purchases of heat pumps, has also driven recent adoption of the devices. Stoddard worried that participation in the state’s incentive programs might dry up because people wouldn’t want to spend the money during the pandemic. “Instead, participation has doubled,” he said. People were stuck at home, some with extra money to spare, given their stimulus benefits and reduced spending. And parts of Maine can still reach 90 degrees Fahrenheit in the summer.
Does carbon reduction itself motivate Mainers to adopt heat pumps? “I’m confident the answer is that it is evolving,” Stoddard hedged. But even if residents aren’t making green-energy choices with decarbonization in mind, the success of incentive programs such as the Efficiency Maine Trust’s have helped the state advance more aggressive policy proposals. In the weeks prior to our conversation, Stoddard told me, Maine had just completed a new climate action plan, and decarbonizing heating systems was among its top three mitigation recommendations. “Now you have everybody talking about this as if it’s just a thing we have to get going on,” he said.