St. Charles County, MO – It’s starting to get a bit colder out and many of us are turning on our heat for the first time this year. But first responders say before you do, get your furnace checked.

The warning comes after a close call for a St. Charles County family discovered a carbon monoxide leak in their home Wednesday morning.

Cottleville Assistant Fire Chief Skip Stephens said carbon monoxide is a silent killer.

“It’s a poisonous gas. It’s colorless, it’s odorless, and it’s tasteless,” he said.

That makes it hard to detect without carbon monoxide monitor.

A family in Cottleville didn’t know there was a leak until they woke up feeling extremely sick and called 911.

“Found higher CO readings of 600 parts per million, which could be fatal at any time,” said Cottleville Fire Battalion Chief Jason Hoevelmann. “Luckily, they actually recognized the symptoms of CO.”

The signs include feeling dizzy or tired, headache, and cause vomiting. In severe cases, you’ll go unconscious and possibly never wake up.

“Make sure you have a carbon monoxide detector on each floor of your home and especially outside in sleeping areas,” said Stephens.

Stephens recommended you should change the batteries at least once a month and replace old detectors, since many only last eight to 10 years. Also, get your furnace checked at least once a year.

Repairman Robert Harmeyer said it takes a professional to do a thorough inspection.

“Homes that are 20 years plus, quite often you start to the heat exchangers start to rust on older units,” he said.

The assistant fire chief said when your carbon monoxide detector goes off, don’t worry about opening the windows to air out the house, just get out immediately and call for help.