How a Rhode Island apartment building for seniors installed 277 heat pumps in just 12 days

Carroll Tower, a 194-apartment public housing development in Providence, Rhode Island, was built in 1974. For more than 50 years, residents there relied on electric baseboards for heating and their own window air conditioners, if they had them, in the summers.

But now, the entire building has been retrofitted with a modern HVAC system: 277 heat pumps from Gradient, a San Francisco-based climate tech startup, will heat and cool the property.

The heat pumps were installed as part of a $1.25 million public-private project between the Providence Housing Authority, Gradient, the Rhode Island Office of Energy Resources, energy consulting firm Abode Energy Management, and Envr Air, which works to accelerate HVAC electrification.

It is among the largest completed heat pump installations in the United States. Installation across the entire building took just 12 days, with no drilling or rewiring required. Since heat pumps are highly efficient, the installation means less energy use and fewer emissions for Carroll Tower.

The upgrade could save the building 450,000 kilowatt-hours, or about $94,500 in energy costs, a year, according to a preliminary estimate, while reducing greenhouse gas emissions by 219 tons annually—equivalent to a gas car driving about 500,000 miles.

A solution for vintage buildings

Residential buildings account for about 20% of the country’s carbon emissions, and heating and cooling is responsible for over half of those buildings’ energy use. HVAC systems can also leak natural gas or refrigerants, which are potent greenhouse gases. 

Electrifying those systems can drastically slash emissions. Heat pumps are a particularly promising climate solution; even when they rely on an electricity grid powered by fossil fuels, they still cut tons of emissions a year compared to other heating systems. 

In 2022, the New York City Housing Authority (NYCHA) launched a “Clean Heat for All” challenge, asking manufacturers to develop an electric, easy-to-install heating and cooling system. Gradient was one winner (along with China’s Midea) and will provide 10,000 of its window heat pumps to NYCHA buildings.

Those projects are rolling, but some buildings have already received the heat pumps. A public housing development in Queens got 72 heat pumps in 2023. That led to an 87% reduction in energy use, with the development’s energy costs cut in half. 

Gradient has since worked with housing authorities in Boston; Chelsea and Lynn, Massachusetts; and more. Its heat pumps work especially well in “older, vintage buildings,” like those found in public housing authorities, says Gradient founder and CTO Vince Romanin. 

These can be buildings where extensive upgrades are difficult (such projects may require asbestos mitigation, for example), and where upgrades are sorely needed because there are no current cooling systems or the heat fails frequently—both of which can be health risks to residents.

‘You can get your window back’

Carroll Tower is one of two elderly-only buildings in the Providence Housing Authority. The average age of residents there is 71. 

Before this upgrade, not every resident had air conditioning; in the summers, the building would turn certain spaces into cooling stations. Now, everyone will have access to their own AC. 

“A lot of them are happy,” says Larry D’Alfonso, an 81-year-old resident and president of the tenant council. The Gradient units, he adds, are “very quiet.”

Depending on the apartment layout or building heating system, heat pumps can have other benefits too.

If someone’s apartment uses steam radiators for which they can’t set their own temperatures, a Gradient retrofit allows for personal temperature control. The units also come with a standard air filter, with an ability to upgrade it.

Romanin adds that the heat pumps, which hang over a windowsill, can make a unit more comfortable because they don’t block that window like an AC unit would. They’re also quieter than clanking radiators. 

“Human comfort is way more than just the temperature in the room,” he says. “The idea that you can get your window back and get more natural light is actually important to someone’s comfort. The noise profile is actually important to someone’s comfort.”

Easy installation

Then there’s the installation. For general HVAC systems, installers may need to drill holes into walls or run refrigerant lines or ductwork through buildings.

Even less elaborate systems, like ductless mini-splits, can still require the handling of refrigerants or wiring, often requiring a licensed contractor. 

Gradient installers don’t need to be HVAC certified. The heat pumps plug into a standard 120-volt outlet. 

“Our system is the first I know of that can electrify [publicly owned] buildings without having to do any work on the facade,” Romanin says. 

Installing 277 heat pumps throughout Carroll Tower’s 194 apartments and common areas took only 12 days, without displacing any residents. (Some units may have more than one  heat pump depending on their square footage). That saves building owners on retrofit costs, too.

D’Alfonso confirms that the installation was “very fast.” The installers were also “tremendous to the tenants, very courteous,” he adds.

The only complaints he’s heard so far from his neighbors were that some people had to move their furniture around to accommodate the heat pumps, which stick out about 9 inches from the wall. 

“They gotta get used to them,” he says. “It’s something new.”