Are ‘Heat Pumps’ the Answer to Heat Waves? Some Cities Think So.

As global warming fuels deadly heat waves across the country, more Americans in places like the Pacific Northwest are rushing out to buy air-conditioners for the first time.

One common concern is that a surge in air-conditioning could make the planet even hotter, by increasing the need for electricity from power plants running on coal or gas, which produce emissions that drive global warming.

But some energy experts, as well as cities like Denver and Berkeley, Calif., have recently started exploring a counterintuitive strategy: Soaring demand for air-conditioning might actually be a prime opportunity to reduce fossil fuel emissions and fight climate change.

The idea is simple: If Americans are going to buy air-conditioners anyway, either for the first time or to replace older units, why not convince them to buy electric heat pumps instead? Although the name can be confusing, an electric heat pump is essentially an air-conditioner that is slightly modified so that it can run in two directions, cooling the home in the summer and providing heat in the winter.

That extra heating function is the key to helping tackle climate change. During the cooler months, heat pumps could warm homes far more efficiently than the furnaces that run on fossil fuels or electric resistance heaters that most households currently use, which would cut down on carbon dioxide emissions. Existing furnaces would only need to be used as backup on the coldest days of the year, since many heat pumps work less efficiently in subzero temperatures.

Most manufacturers already offer heat pump versions of the air-conditioners they sell, but they’re typically about $200 to $500 more expensive to make. So, the idea goes, policymakers would have to step in with subsidies or regulations to make adoption universal. But if done right, proponents say, households would see utility bills either drop or stay largely unchanged, and they would even enjoy a more comfortable heating experience.

“It’s essentially the same piece of equipment with a few extra parts, and you can make the swap with almost no extra work,” said Nate Adams, a home performance consultant who proposed the idea in a recent paper, written with experts at Harvard University CLASP, a nonprofit formerly known as the Collaborative Labeling and Appliance Standards Program that advises governments on energy efficiency.

Today, Americans buy more than five million one-way air-conditioners and three million two-way heat pumps each year. “If virtually all of those sales were heat pumps, we could put a big dent in fossil fuel use,” Mr. Adams said.

Working with energy modelers, Mr. Adams and his co-authors estimated that, if two-way heat pumps become the standard option when people installed new central air-conditioning, they would be in 44 percent of American homes by 2032, up from just 11 percent today. On average, those homes could cut their fossil fuel use during the colder months by at least one-third.

And, as states move to clean up their electricity grids by adding more wind and solar power, the climate benefits from those electric heat pumps would increase.

Mr. Adams said the analysis mainly looked at replacing central air-conditioners, which are the most common type installed in the United States. Converting window units to heat pumps could raise additional complications, he said.

Some cities are taking the idea seriously. In Denver, which was hit by a 100-degree heat wave in June, nearly one-third of homes still lack air-conditioning, which is becoming increasingly necessary at a time when global warming means more intense and frequent heat waves, and more wildfire smoke that makes it hazardous for people to open their windows.

This month, Denver released a plan for cutting emissions associated with heating and cooling its buildings. One idea under discussion is helping residents install heat pumps when it’s time for a new air-conditioner or furnace. City officials caution that they still need to sort out what policy steps to pursue, though last year Denver voters approved a new climate fund, paid for by a sales tax hike, that could potentially help defray upfront costs.

“Many of our homes were built for a different climate, when it didn’t get that hot and you could open the windows to cool down at night,” said Grace Rink, executive director of Denver’s Office of Climate Action, Sustainability and Resiliency. “Now it’s getting hotter and people need to cool their homes, so how can we do that in a sustainable way?”

Figuring out how to cut emissions from buildings is one of the thorniest problems in climate policy. Homes and offices account for 13 percent of the nation’s annual greenhouse gas emissions, with much of that from oil or natural gas burned in furnaces, hot water heaters, ovens, stoves and dryers. While the United States has made major strides in reducing pollution from power plants, building emissions have barely budged since 2005.

Many climate experts say the long-term solution is to replace most of those fossil-fuel appliances with electric versions powered by a greener grid. But in practice, that’s difficult. While cities like Berkeley have rewritten building codes to ban new buildings from using gas, more than a dozen mostly red states have passed laws explicitly forbidding cities from doing so. And that still leaves the question of what to do about millions of existing homes.

Stephen Pantano, the chief research officer at CLASP, said that encouraging people to install heat pumps when they’re going to buy central air-conditioners anyway could be a less intrusive way to start electrifying heating. “We found that a relatively small investment of around $3 billion to $12 billion nationwide could have a big impact on energy use,” he said of the group’s new proposal. “It’s hard to find many ideas with that much bang for the buck.”

An even more drastic strategy, he added, would be to figure out how to replace more gas furnaces with heat pumps, so that the heat pump handles virtually all the heating and cooling. But that could require larger heat pumps for many homes or additional electrical upgrades and other retrofits. His group’s proposal for simply swapping out air-conditioners is a more modest first step.

Berkeley, which pioneered the idea of banning gas in new buildings, is now considering this approach. Only 10 percent of the city’s homes currently have air-conditioning, but officials estimate that fraction could triple in the hotter decades ahead. “Berkeley should work with A/C installers and heat pump manufacturers to ensure these homes install heat pump systems instead,” officials wrote in a recent draft strategy for electrifying existing homes.

“It’s a great idea,” said Jigar Shah, who directs the Department of Energy’s loan programs office. His office is exploring ways to help low-income Americans adopt technologies like heat pumps. “Heat pumps aren’t some untested technology,” he said. “We’re really in a place where it’s time to scale this up.”

Others were more cautious. “There are places where electrification may be beneficial, and places where it might not, and there are a lot of details that need to be worked out,” said Francis Dietz, a spokesman for the Air-Conditioning, Heating & Refrigeration Institute, an industry trade group. If more homes relied on heat pumps instead of gas furnaces, for instance, that could put a strain on electric grids in the winter, especially in colder parts of the country, he said.

There are other obstacles, too: Many Americans still aren’t familiar with heat pumps, and some have had bad experiences with older models that didn’t work as well in cold weather. While heat pump technology has improved significantly in the past decade, many contractors remain wary of them. And, of course, the name “heat pump” doesn’t sound like a device you want to install when it’s sweltering out.

Stephen Rardon, a heating and cooling specialist near Raleigh, N.C., thinks it’s time for that to change. In 2008, he bought a heat pump for his home when it was time to replace his central air-conditioning unit. It cost about $3,500, compared with $3,000 for a comparable one way air-conditioner. At the time, he also installed a new gas furnace, thinking it would still be necessary in the winter.

He was wrong. In the years since, his furnace has barely been used, although it helps that temperatures in his area rarely get below 20 degrees. “I basically wasted the money on that furnace,” he said.

He now recommends heat pumps to his customers. “Based on my experience, it can make a lot of sense,” he said. “You’re moving away from fossil fuels. You don’t have to worry about carbon monoxide leaking out of a heat pump. And it actually provides a more comfortable heating experience.”