By Donald Gilpin

“Heat pumps aren’t magic, just efficient,” reads a headline in last month’s The Charge, Princeton University’s online newsletter reporting on some of the University’s energy and environmental research.

The short article about heat pumps goes on to describe how efficiently they work and how new government incentives can help to make them an attractive alternative for homeowners with traditional air conditioner and furnace systems.

In her research, in both rural China and in her own home in Princeton, Denise Mauzerall, Princeton University professor of civil and environmental engineering and international affairs, has taken a close look at the heat pump option.  “Heat pumps do seem like magic,” she says, as quoted in The Charge article.

In a January 13 email she explained, “Heat pumps are highly efficient and provide a great way to cost-effectively heat and cool homes. The added benefit for the environment is that as the power grid moves away from electricity generated with fossil fuels and towards power from renewable energy, heating and cooling our homes with heat pumps will be even more beneficial for air quality and climate.”

Mauzerall’s family converted their gas furnace and conventional A/C to a heat pump last year. “The HVAC company that maintained our conventional gas furnace and A/C were unfamiliar with heat pumps and quoted extremely high prices,” she said. “The company we went with that had previously installed heat pumps for others sold us the air source heat pump for a price that was approximately the same as what the other company had quoted us to replace our gas furnace and A/C with a comparable new gas furnace and A/C.”

She continued, “In New Jersey heat pumps are a great option. The upfront costs for heat pumps, when purchased from a contractor accustomed to installing them, is highly competitive with conventional gas heaters plus air conditioners (a heat pump replaces both). For new construction, or for replacing heaters and air conditioners at the end of their lifetime, a heat pump is the obvious best choice as it is both super-efficient and highly cost effective.”

Heat pumps work by moving the heat, absorbing it from inside and moving it outdoors in the summer for air conditioning or absorbing it from outside and moving it indoors for heating in the winter, even when the temperature is below freezing. 

Mauzerall noted that she has a resistance heater for extra heat on the coldest days, but she has seldom needed to use it. Up-to-date technology upgrades have made heat pumps more effective for heating and cooling at extreme temperatures. Though heat pumps might not work in every house and every situation, they have become increasingly popular. 

“We need more contractors who are knowledgeable about heat pumps,” she added. “It’s a great opportunity for them, but the expertise is not yet widely available.”

In a paper published in Nature Sustainability in December 2021 and supported by Princeton University and partners in China, Mauzerall and her research team showed that heat pumps are environmentally the best option to maximize climate, air quality, economic, and health benefits. Small coal-based stoves in China have created very high pollution levels in rural areas and in nearby urban areas where the polluted air has been transported by wind.

The researchers’ policy guidance emphasized that heat pumps, which run on electricity, are more energy efficient than other options and cheaper to operate in the long term, though they come with higher upfront costs.

“We found that replacing coal stoves in urban and rural residences with clean heaters dramatically improves air quality throughout northern China in winter while also decreasing premature deaths,” said Mauzerall in a Princeton University press release.  She added that out of all clean heaters, heat pumps provide the largest reductions in air pollution and carbon emissions.

While other types of heaters burn fuel to generate heat, Mauzerall explained, heat pumps just move the heat, with a piston compressing and expanding a fluid to make it heat up or cool down. They can be more than twice as energy-efficient as traditional heaters that burn fuel, she said.

In a January 14 New York Times op-ed focused on the recent controversy over the potentially dangerous use of gas stoves, Farhad Manjoo transitioned from the subject of stoves to the subject of heat pumps as a consideration for homeowners. “Instead of getting an induction stove, then, it might make a lot more sense for you to spend your money on a heat pump, an underappreciated and kind of magical electric device that can replace both a gas-powered furnace and an air conditioner,” he wrote.

Both Manjoo and Mauzerall also strongly recommend increased insulation.

The recently enacted Inflation Reduction Act includes a number of incentives to lower the cost of homeowners’ energy-saving measures, including up to 100 percent of the cost of a heat pump for low-income households. There are also additional new tax credits, as well as different rebate programs available for higher income homeowners.