TROY, Ohio (WDTN) – We now know a blocked chimney flue and furnace issues contributed to the carbon monoxide poisoning deaths of three children in Troy. One more child is still in critical condition.

2 NEWS is digging deeper into what exactly went wrong and the important lesson anyone with a gas heater can take away from this tragedy.

City leaders and technicians tell us they want you to remember to get your furnace inspected every year. They say it’s not just a sales pitch. It could be the difference in keeping your family safe.

Your furnace is an important appliance to have around but it can also be a dangerous one.

“You never know when something is going to change and change can happen a lot quicker than just a year. You can have something change in as little as a day,” said McAfee Lead Service Tech, Chris Bryant.

Gas heaters produce carbon monoxide and that poison can be deadly to breathe in.

Heaters are designed to act as a tail pipe. They channel fumes and exhaust with vents and pipes. A lot of times they’re attached to a chimney flue.

Lead Service Tech at McAfee, Chris Bryant said that flue needs to be inspected regularly or you could have problems.

“Blockages can be caused by a number of things. You can get animals, you can get debris, you know, sticks, leaves; things like that can fall in there over time.”

Investigators say that’s exactly what happened to the home in Troy. The furnace was venting to the chimney and that chimney started to deteriorate. The debris from that crumbling chimney blocked it; keeping the CO inside. That furnace also had a restricted air filter and air inlet. That can cause the furnace to not properly break down the fuel which produces more CO.

“A simple furnace check which is routine can catch a lot of these problems and prevent carbon monoxide from entering the home and injuring or worse..the folks that live there,” said Bryant.

Bryant suggests doing the routine check every year to make sure the carbon monoxide is not leaking out. He says it costs less than 150 dollars.

If your furnace produces carbon monoxide, technicians also want you to put a CO detector right by it. It will alert you if CO levels are too high.