If you live in an old-school New York City apartment building with steam heat—and no thermostat to control the temperature—your apartment may get so hot in the winter that you have to open the windows to cool it down. Some people actually turn on the AC while their radiators run, wasting even more energy. But a startup called Gradient is trying to make it easier for buildings to switch to greener heat pumps instead.

Gradient’s design, like other heat pumps, works for both heating and cooling: In the winter, it pulls in heat from the outside air, and in the summer, it runs in the opposite direction. It’s efficient and runs on electricity, unlike old boilers that run on fossil fuels.

Retrofitting an old building with other heat pumps is typically cumbersome, involving workers on scaffolds drilling holes in walls and adding new wiring. The work can take days. But the new design can just be added to windows—without blocking the view—and plugged in to the wall. Installation takes around 30 minutes. (Depending on the layout of the space, one might be installed in each room.)

“Older multifamily buildings are really difficult and expensive and slow to retrofit with typical heat pumps,” says Vince Romanin, Gradient’s cofounder and CEO. “Our advantage is that this makes it cheaper, easier, and faster.”

The first iteration of the product focused on air conditioning, with a better-looking, quieter, more efficient version of a window AC. It could also provide heat, but at first, that only worked in milder climates. Over the last two years, the team has tweaked the design so that it can work in temperatures as low as -7 degrees Fahrenheit.

“We really stepped up our design in almost every way,” says Romanin. “We have larger, more efficient, and more powerful heat exchangers. We have redesigned air flow for higher efficiency and lower noise and more air flow. We’ve designed our entire system to just have larger total power.”

Later this month, the company will begin installing the units in public housing complexes in New York. Over the next seven years, it will deliver 10,000 of the units to the New York City Housing Authority. The design was one of the winners of a government competition to help transform aging heating systems in the city’s public housing. Another company, Midea America, is also providing a similar heat pump for the program.

The Housing Authority manages hundreds of buildings and 177,000 apartments, and the majority of its carbon footprint comes from heating systems. The same is true for other apartment buildings. But a new New York City law requires large buildings to make changes to steeply cut emissions. Some of those building owners may also turn to newer heat pumps like Gradient’s to do that. Gradient is also beginning to work with apartment buildings, schools, and nursing homes in other parts of the country.

The installed cost of the equipment is roughly half of a typical heat pump, Romanin says. The company plans to launch the product to consumers more widely next year at a retail price of $3,800. For a small home or condo, incentives from the Inflation Reduction Act could cover some or all of the cost. And if you live in an apartment building that isn’t making changes quickly, it’s one way to take control of shrinking your own carbon footprint.