We bought our house last year with the original Lennox gas furnace from 1993. It seems that every time it gets windy outside our carbon monoxide detectors go off. Once we had it bad enough that I had to take my kids to the hospital. We can feel the wind coming down through the vents and through the furnace. This only happens when there are high winds, but we have to turn off the furnace and run our fireplace. Any ideas on why this is happening and how we can fix it? Thanks.. Lisa

There shouldn't be a connection between the combustion chamber and wind outside, and your vents. The heat exchanger should be air taught with the CO and wind on one side, and the air supplied to the vents on the other. I would open up the furnace and try to find cracks, gaps, open inspection ports, or any other way for the wind and CO to cross the heat exchanger. This is a very serious problem. Could be as simple as replacing a cover or tightening some screws. If the heat exchanger is cracked on a 12 year old furnace, you might consider a new one. If you can't find a problem, or can't fix what you find, call a professional.

If the combustion air for the furnace is supplied out of the living space, it would be possible for the wind to force CO into the living space that way. You still should not have wind gusts coming coming out the vents.

You might try a wind directional chimney cap. They're specifically designed to control downdraft issues caused by high wind situations.

I would, though, call an HVAC person for a "free estimate" so that I could learn what his opinion is of both the cause and the solution to the problem.

Hope this helps.

PS/Edit. I was typing as labman was posting... He gives good advice: Getting a good diagnosis is important; more so than just looking for a quick fix.

Lisa, you stated in your question that " Once we had it bad enough that I had to take my kids to the hospital."

STOP WHATEVER IT IS YOU ARE DOING AND CONTACT AN HVAC PROFESSIONAL. DON'T GO TO WORK, DON'T PASS GO, DON'T COLLECT $200. CALL SOMEONE NOW!!

This is serious and a potentially lethal situation. If your CO detectors go off from wind, you have a MAJOR issue with your HVAC system.

Don't waste time by trying to find the cause of the problem yourself.

In a recent test by a Chicago TV station: "Our meters show us 475 ppm in this room. Every detector's gone off except one. It shows less than 60 ppm."
They also reported that at a lower level of 100 ppm, most of the CO detectors didn't even go off.

For healthy adults, CO becomes toxic when it reaches a level higher than 50 ppm (parts per million) with continuous exposure over an eight hour period.. When the level of CO becomes higher than that, a person will suffer from symptoms of exposure. Mild exposure over a few hours (a CO level between 70 ppm and 100 ppm) include flu-like symptoms such as headaches, sore eyes and a runny nose. Medium exposure (a CO level between 150 ppm to 300 ppm) will produce dizziness, drowsiness and vomiting. Extreme exposure (a CO level of 400 ppm and higher) will result in unconsciousness, brain damage and death.


I would strongly suggest just replacing the furnace with a new one. Get a 90+ efficient furnace. They will have sealed combustion and do not require intake air from the house.