“There’s a massive difference in the amount of heat that our system is putting out when a user asks for heat to be comfortable versus a radiator which dumps tons of extra heat into the room,” says Vince Romanin, CEO of Gradient. “If they’re able to set that temperature on a per-room basis, not a per-building basis, you end up—because you’re only heating and cooling the rooms needed—with about 20 percent less energy use.”

The New York City Housing Authority says that residents are overall happy with the units, especially the ability to control temperatures. In the summer, a heat pump reverses to work like an air-conditioning unit. So people who’ve never had AC suddenly have a clean, efficient device that both heats and cools. “The heat pumps allow NYCHA to move away from natural-gas-based steam heating systems and are also two to six times as energy efficient as these systems,” says Shaan Mavani, chief asset and capital management officer of the Housing Authority.

With these heat pumps, New York is inverting the usual pattern for new energy technology, which is usually too expensive for regular people to afford. “It’s relatively cheap, relatively simple technology that’s plug-and-play, that works in the 100-year-old public-housing brick building,” says climate economist Gernot Wagner of the Columbia Business School. “It’s the rich who are supposed to be early adopters of the new, sexy, top-of-the-line climate tech.”

Gradient’s all-weather heat pump, meant to operate in colder climates, is set to be priced at $3,800 later this year. That’d be offset by a growing number of state and federal rebates and tax credits that encourage decarbonization. With a full-on heat pump system working through ducting in a fancy person’s home, you’re looking at the costs of potentially having to upgrade your electric system to handle the additional power demand, whereas a smaller window version just plugs into the wall. Actually installing a heat pump isn’t much different from installing a typical AC unit, usually taking about a day, but the technician will need some special training to do it. (In general, the US is desperately short of the skilled workers available to install enough heat pumps and other green tech to decarbonize fast enough.) By contrast, you can install a window-sill heat pump in under an hour, Gradient says.

One of the hurdles for urban apartment dwellers is the potential for an operational cost shift: If the landlord had been paying for a central steam heating system, and the renter is now running a heat pump on their own unit’s electricity, their bills may increase. Some 90 percent of the New York City Housing Authority’s residents live in buildings that are “master metered” anyway, meaning they don’t pay individual electric bills. For the remaining 10 percent, the NYCHA will likely introduce a utility allowance to ensure that the switch to a heat pump doesn’t increase expenses. At the same time, as residents make that switch, the agency will save on the costs associated with repairing the existing heating distribution systems. “The heat pumps obviate the need for these investments,” says Mavani.

What the NYCHA has embarked on is a plan that other metropolises could copy for switching their own multifamily buildings to heat pumps. “That said, every city has a different mix of building typologies, local codes, heating and cooling needs, and construction and utility costs,” says Mavani. “Hopefully, based on the experience in New York, other multifamily building owners—whether public or private—will have better data points to support their own decisionmaking.”

Heat pumps will only get cheaper from here. Unlike stagnant fossil-fuel heating techniques, heat pumps are a technology that’s evolving, getting more and more efficient at extracting heat from outdoor air and moving it inside. “Heat pumps are the classic example of a technology that over time will only get better, will only get cheaper,” says Wagner. “We know where we need to go. We have to electrify buildings; we have to get off gas and oil heat especially. This is the way to do that.”