Russ Austin said it started with an emergency call to the Warman fire department early Tuesday morning.
A man driving north of the city, which is just north of Saskatoon, said he had a severe headache and nausea and he was worried about the health of his wife and two kids back in Warman.
Austin, who is chief of the Warman department, told the caller to pull over and call 911, and get to a hospital.
Then Warman fire crews raced to the home.
They arrived to find the doors and windows open and the woman and two teens in the front yard.
"They were outside on their step, on their front lawn, in distress. They described it as excruciating headache, dizziness, nausea," Austin said.
Crews checked out the house and discovered that a leaking furnace was producing carbon monoxide levels at 1,000 parts per million — a potentially lethal level.
"If the night was colder and the furnace ran longer, it was only a matter of — I wouldn't even say hours, it was probably a matter of minutes before they could have taken a lethal dose," Austin said.
The people in the home were treated and are expected to be all right.
Austin said there was a carbon monoxide detector in the home, but that it wasn't working.