Dozens of churchgoers were overcome by carbon monoxide in a Provo meetinghouse Sunday — and while no one was seriously hurt, it’s a reminder for people to check their furnaces as cold weather hits.

Provo firefighters got a medical call Sunday, just after 11 a.m., at The Church of Jesus Christ of Latter-day Saints’ meetinghouse at 650 E. Stadium Ave. On the way, crews learned “the whole building was full of carbon monoxide,” said Jeannie Atherton, a public information officer for the Provo Fire Department.

Intermountain Healthcare reported the hospital chain’s facilities treated 59 people for carbon monoxide poisoning. Twenty-three of them received hyperbaric treatment, to get oxygen to tissues poisoned by carbon monoxide, at Utah Valley Hospital in Provo, Intermountain Medical Center in Murray and LDS Hospital in Salt Lake City.

“A lot of people who felt sick felt a lot better once they got outside,” Atherton said.

The source of the carbon monoxide was a boiler in the church building’s basement, Atherton said. The building remains closed, she said.

Atherton said carbon monoxide leaks often happen in the fall, in businesses, commercial buildings and residences. “We go on a lot of calls to private homes," she said, “where people are firing up their furnaces for the first time in the season.”

People should get their furnaces checked before starting them up, Atherton said, and get a good carbon monoxide detector. (Other sources of carbon monoxide include automobile exhaust, small gas engines and other fuel-burning machines being used in areas with poor ventilation.)

Carbon monoxide is the top cause of death by poisoning in the United States, Intermountain Healthcare reports — and it’s called a “silent killer" because it has no color, odor or taste.

“Carbon monoxide poisoning symptoms are similar to the flu — nausea, tiredness, aches and pains,” physician Lindell Weaver, medical director of the Hyperbaric Medicine Center at Intermountain Medical Center and LDS Hospital, said in a statement. “If you suspect you have been exposed to high levels of carbon monoxide, you should leave immediately and seek help.”