The sun was about to set Monday evening and the temperature was still 90 degrees. The air was thick and oppressive. Shaasia Wood and her 4-year-old son were hanging out on the sidewalk, hoping for a breeze, near the homeless shelter where they live in Upper Manhattan.

That was because inside their un-air-conditioned room, “It feels like living in hell, really,” Ms. Wood said.

Ms. Wood, a 40-year-old home care aide, has plenty of company in her misery: Thousands of families with children live in New York City shelters that lack air-conditioning in the rooms where people live and sleep, even in the depths of a heat wave. On Monday, no air-conditioners were visible above the ground-floor offices of her shelter, the Hamilton Family Residence.

At the Doña Elsie Family Residences in the Morrisania neighborhood of the Bronx, Floyd Perkins, 56, who lives with his partner and seven children, said, “All I know is that we’ve been sweating ever since summer came, and sweating, sweating, sweating.”

Some family shelters are in former hotels that are fully air-conditioned, but many of those shelters house newly arrived migrant families. Shelters for the rest of the homeless population are typically in buildings that do not have air-conditioning, the city said.

Mayor Eric Adams, who on Monday reminded New Yorkers that “a heat wave can be deadly and life-threatening if you are not prepared,” recommended on Tuesday that shelter residents simply suck it up.