The New York City Public Housing Authority is launching a pilot program to, for the first time ever, provide free air conditioning to some of its residents.

The pilot is starting small, in just two buildings of the authority's portfolio of roughly 2,500 properties. But it is arguably the most concrete step the city government will have taken in its long-delayed plans to prepare for the deadliest climate change threat: extreme heat.

Until now, tenants may buy their own window air conditioners, but they must have them professionally installed and also pay an annual fee to offset the cost of additional power they consumer. (Public housing rents, unlike most of those in the private sector, include the cost of utilities; therefore the authority would consider it unfair if some residents used more than their fair share without paying extra for it.)

Some 90 percent of New York City's general population has air conditioning in their homes, but, according to official tallies, fewer than one-half of public housing residents do. Because of the financial disincentive to register one's AC unit, officials suspect the NYCHA number is somewhat higher, though they do not know by how much.

Under the pilot, which is expected to begin in the coming weeks, residents of Meltzer Tower in Manhattan East Village will be offered high-efficiency window air conditioner units. (If they already own one or two, they will be swapped out on a one-to-one basis.) In Independence Houses in the Bronx, tenants on the top floor who choose to take part will be outfitted with air source heat pumps, a type of equipment that can be used to either cool or heat a unit. None of the tenants who opt into the program in either location will be charged the extra electricity fee.

The impulse to launch the program, which comes at a precarious point in NYCHA's history, stems from a variety of sources. One is the growing realization that heat, even more so than hurricanes or rising sea levels, has the potential to kill large number of New Yorkers. The city estimates that about 115 people die from heat stroke or heat-exacerbated illnesses each year; a Columbia University study projects that heat-related mortality could reach 1,500 deaths each year as heat waves become more frequent. Elderly residents are particularly at risk, which is why both locations chosen for the pilot are senior housing.

"The city has made it very clear that providing air conditioning in case of high heat events is very important," said Bomee Jung, the vice president for energy and sustainability at the housing authority. "Very quickly, the question that NYCHA asked itself about being a landlord is, 'How do we provide cooling if it's necessary?'"

Another factor is that Consolidated Edison now penalizes customers with high peak usage and rewards those that reduce peak consumption. Jung said that one goal of the pilot program is to see if they can make it cost-neutral, such that the cost of buying and installing air cooling equipment, as well as the power that equipment consumes, would be no more expensive than what the authority is paying to power tenants' current window units.

One reason she believes power costs will decrease, even though more apartments are being cooled, is that the new equipment will be highly efficient and also networked. Even though tenants will be able to adjust the thermostat themselves from inside the apartment, the network will make minor adjustments as to when one air compressor turns on or off, in order to level out the peak demand.

As for whether the authority will expand the program to all senior housing buildings, or even to all authority-owned property, is yet to be seen. Already, without air cooling taken into account, the authority estimates it needs $32 billion in capital improvements, and the city has only pledged a small fraction of that amount. But Jung said it is possible that the city may at some point in the future require that all buildings, public and private, provide air cooling in the summer, just as it mandates heating in the winter.

"We are testing the technologies with the understanding that the need will increase in the future and so we need to figure out the financial impacts," she said. "The real estate industry has recognized that we need to adapt to these climate change impacts."

She added, "The costs will just become something that we have to manage around, just like the cost of heating is just something that we have to manage around. "