The Next Heat Pump Frontier? NYC Apartment Windows

Future generations will marvel at the ridiculous ways we’ve been keeping warm. With a furnace, you’re inefficiently burning toxic, planet-warming gas. In a big city like New York, your building might have a boiler that burns oil or gas to heat water or produce steam, which feeds wheezing radiators in every unit. Electric-resistance space heaters are more efficient, but even they’re not nearly efficient enough, as you’ll see in your utility bill if you run one too much.

For many decades now, there’s been a far more efficient device that climate nerds love: the heat pump. Instead of generating heat like those other techniques, it transfers warmth from outdoor air into an indoor space using nifty tricks of physics, even when that outdoor air is freezing. A heat pump can attach to a home’s central ducting system, replacing a gas furnace, or ductless models can attach to walls.

Now, New York is experimenting with what could be an even more powerful kind of heat pump for urbanites: one that slips over a window sill. In 2022, NYC announced a $70 million investment for developing and producing 30,000 heat pumps for its public housing. One of the companies awarded funding, Gradient, rolled out 36 window units and collected data on their performance over this past winter. It’s now sharing early results. (You can see what Gradient’s device looks like at the top of this story. Think of it like a window AC unit but much more advanced.)

Gradient says that on the coldest days, its window heat pump performance indicates that the unit can reduce the cost to warm a New York home by between 15 and 55 percent compared to gas-fired steam heat, and by between 51 and 74 percent compared to oil-fired steam heat. On moderate days, projected savings are between 29 and 62 percent compared to gas, and 59 and 78 percent compared to oil. The hope is that heat pumps like these can help the city and the state transition away from fossil fuels; New York is part of a consortium of nine states aiming to get heat pumps to account for 65 percent of residential heating, AC, and water-heating shipments by 2030.

Because it’s moving heat instead of generating it, a fully electric heat pump is