Long Island, NY – Three teenagers and three adults were taken to a hospital after a carbon monoxide leak was discovered in a Long Island home Tuesday, authorities said.

The Garden City homeowner, Martin Arellano, told NBC 4 New York he had just turned on his heat for the first time this winter and there was apparently some kind of leak.

He had family visiting from South Carolina — two teenagers and two adults — and the teenagers, who had been sleeping in the basement, fainted from apparent exposure to carbon monoxide, he said. When the teenagers fainted, the other people in the home realized something was wrong and called 911.

The two teenagers who had been in the basement, 15-year-old and 17-year-old girls, along with another 17-year-old, a 19-year-old and two other adults, were all taken to the hospital with symptoms related to carbon monoxide exposure. Hospital officials said the four youngest all females, were admitted.

Their conditions weren’t immediately clear, but Arellano said everyone was expected to be OK.

National Grid, which responded to the home, said Arellano had a water heater installed over the summer and the utility believes improper installation may have contributed to the carbon monoxide leak.

Arellano said he has a plug-in carbon monoxide detector in the basement, but it was covered with boxes and papers so may not have registered the gas.