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Boston is racing to decarbonize its public housing by 2030. The latest tool it’s deploying to reach that goal? Window-straddling heat pumps.
Last week, the Boston Housing Authority announced that it’s piloting the electric technology at Hassan Apartments, a 50-year-old public housing community with 100 units for older people and adults with disabilities. The modular appliances, made by California-based startup Gradient, plug into a typical 120-volt wall outlet and will replace the apartments’ outdated, much less efficient electric-resistance system.
“We believe that low-income people and the families and individuals who live in our buildings deserve access to 21st-century technologies and home comforts, just like anyone else out there,” said Joel Wool, the agency’s deputy administrator for sustainability and capital transformation. ​“We’re also doing our part to reduce air pollution and combat climate change.”
The Boston Housing Authority has ordered about 100 window heat pumps for the project. Two other Massachusetts housing agencies are also piloting Gradient’s appliances, the company announced last week: the Chelsea Housing Authority, which is testing about 400 heat pumps, and the Lynn Housing Authority & Neighborhood Development, which is trying out roughly 200 heat pumps, about half of which are already installed.
Outside of Massachusetts, in 2022, the New York City Housing Authority (NYCHA) committed to purchasing a total of 30,000 of the devices from Gradient and global appliance maker Midea over a period of seven years. The agency has been learning from an initial 72 heat pumps installed, and their performance has been positive enough that Gov. Kathy Hochul (D) announced on Friday $10 million to fund demonstration projects statewide.
Heat pumps, which are essentially reversible air conditioners, are key to electrifying heating. They provide potentially life-saving cooling, too. Because they shift around ambient heat instead of generating it anew, the appliances are routinely two to four times as efficient as electric-resistance and fossil-fuel-fired options. (Gradient claims its heat pumps are also about 50% more efficient than plain old window AC units.)
But retrofitting a building with a conventional heat-pump system can be a complex undertaking, requiring electrical upgrades and new refrigerant lines that run to individual air-handling units in each apartment, for example. Window heat pumps might require some trade-offs in terms of efficiency, but they also sidestep those serious installation hurdles.
That ultimately makes them faster and cheaper to deploy, as well as less disruptive to tenants, according to Wool. Two workers can install one of Gradient’s 140-pound heat pumps in about half an hour, NYCHA estimated, draping its saddle shape across a windowsill. And a July study by the American Council for an Energy-Efficient Economy found that window heat pumps are typically the lowest-cost option for efficiently decarbonizing space heating, coming in at an average lifetime cost of about $14,500 per apartment compared to between $22,000 and $30,000 for large-scale heat-pump systems.
For its pilot, the Boston Housing Authority is paying $5,450 per residence to retrofit with window heat pumps — about one-eighth of what it has spent to update other buildings with conventional heat-pump systems: approximately $40,000 per unit, according to Wool.
Electric and gas utility Eversource is fully funding the project through the state’s energy-efficiency collaborative, Mass Save. Once the retrofit’s complete, the Boston Housing Authority expects to save up to $60,000 in energy costs per year.
In New York, window heat pumps are already making deep cuts to energy use. At the NYCHA-owned Woodside Houses, going from a gas-powered steam system to the appliances slashed the amount of energy consumed for heating by 85% to 88%, according to preliminary results from NYCHA.
“This [reduction] sounds unrealistically large,” said Vince Romanin, founder and chief technology officer at Gradient. But ​“we roughly know the reasons.” Waste abounds with fossil-fuel systems: Boilers don’t perfectly convert fuel into heat, steam leaks on its way to apartments, and residents, lacking control over the temperature, are prone to throw open windows if they’re overheating, he noted. User-controlled window heat pumps avoid all of those issues.
Gradient has raised more than $31 million in venture funding and signed over $9 million worth of federal and California grants to develop its window heat pumps, which it has shipped to multifamily building owners and developers in 18 states, Romanin said. He declined to specify the cost per unit.
At the Hassan Apartments in Boston, installations are already underway and should wrap up by mid-November, said Wool of the city’s housing authority. The agency will monitor energy costs closely, as it weighs whether to deploy the tech at other properties. Across its 10,000-unit portfolio, heat pumps — of the conventional variety — serve just a few hundred apartments so far.
“We do think that window heat pumps are a great technology,” Wool said. ​“It’s also still an early one. We want to see how it performs.”
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