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Wed, Feb. 26

Carbon monoxide monitors a must with gas fireplaces

A month ago I inspected a home and found carbon monoxide entering the home from the gas fireplace. Carbon monoxide is colorless and odorless - the only way to test for it is with a carbon monoxide tester. I recommended a contractor check the fireplace operation. A fireplace contractor came out and checked the fireplace, and provided a written report that said the fireplace was completely safe. Fortunately, my client's Realtor insisted I re-inspect the home.

The fireplace contractor stated no carbon monoxide was found using a TIFF 8900. I have a TIFF 8900. These are gas leak tracers; they do not test for carbon monoxide. I use a high-quality ($600) carbon monoxide tester. When I returned to the home, there was still carbon monoxide entering the home. It was at this moment that I knew what I was going to write about this week: fireplaces.

WARNING: I usually try to get a chuckle or two out of you in my columns, but there are no funnyisms in this one. After the first draft I realized this was a hot topic and I should not put a damper on it.

Traditional wood-burning fireplaces are not very efficient at warming a home because most of the heat is going up the chimney. You can warm your buns a little if you sit right on the hearth, but if you move away from the fireplace you don't feel much heat. I rarely see a traditional wood-burning fireplace in newer homes, and when I do they almost always have a gas (fake) log kit installed.

Gas fireplaces produce a lot of carbon monoxide. On most gas appliances (cooking ranges, water heaters, etc.) the burners are adjusted to produce maximum heat. This makes a blue flame and minimal carbon monoxide. Gas fireplace burners are adjusted to simulate a wood fire; the more orange flame (and carbon monoxide), the better.

Most newer homes have gas-only fireplaces. These are convenient - most have pilot lights with a push-button igniter. The burner is usually turned on with a wall switch; some have a thermostat or remote control. These have "sealed" burn chambers - you can't actually touch the fake logs without removing a glass cover/door. These fireplaces are safe because the burn chamber is isolated from the interior space.

There is a concern with how these fireplaces are vented to the exterior. Many are vented through a metal chimney that is routed up above the roof - a safe installation. However, many are vented through an exterior wall. The concern is if this vent is near a door or opening window. I almost always find over 100 ppm (parts per million) of carbon monoxide in the exhaust gas of a gas fireplace. I've found as much as 400 ppm. If a window or door near the fireplace exhaust vent is open while the fireplace is operating, the exhaust gas and carbon monoxide could be drawn back into the home.

This is a bigger concern if the window near the fireplace exhaust is in a different room. Many times I have seen a corner fireplace that vents through an exterior wall near a window in the adjacent room, frequently a bedroom. When I see these installations I recommend installing a carbon monoxide detector in all rooms with windows near the fireplace exhaust vent. I also recommend putting a "screw lock" on the tracks on the windows near the fireplace vent in the winter, as a reminder not to open them.

There are different concerns with a gas log kit installed in a wood-burning fireplace. These are always vented through a chimney above the roof, so there is little concern about the exhaust gas. However, many times I have found carbon monoxide entering the home at the fireplace.

The first thing you need to check is the damper. If the damper is closed and you turn on the gas burner, carbon monoxide will definitely enter the home. There will not be smoke, and may not be any odor, but there will be carbon monoxide. When a gas log kit is installed, a clamp should be installed on the damper to keep it fully open. Some fireplace contractors will remove the damper or disable it so it remains open. This is easy to check. If you have a gas log kit and a damper, make sure the damper cannot be closed.

A gas log kit has to be "listed" for use with that specific fireplace. Unfortunately, this is almost impossible for you, or even home inspectors, to verify. If a log kit is not listed, you can get carbon monoxide in the home even if the damper is fully open. Even when the gas log kit is listed for a fireplace, I have found carbon monoxide entering a home. One time a manufacturer's representative came out and simply rearranged the logs. That was all it took to correct the problem. Which means all it took to create the problem was someone rearranging the logs.

I recommend you install a carbon monoxide detector in any room with a gas fireplace. There is some debate over "acceptable" indoor levels of carbon monoxide, but a generally accepted number is no more than 9 ppm. Some carbon monoxide detectors don't activate unless there are high levels of carbon monoxide (one brand doesn't go off until 70 ppm). And the test button on most carbon monoxide detectors does not test the "tester," it just tests the alarm (i.e. that it can make noise). So a carbon monoxide detector is no replacement for common sense.

You need to find where your gas fireplace vents to the exterior. If it vents through a wall, you need to take the proper precautions. You should have your fireplace checked and serviced yearly by an appropriate professional. If you can find a manufacturer's name on your fireplace, try to find a professional who is qualified and experienced with your brand of fireplace. And ask the contractor to test for carbon monoxide in the home.

Randy West owns Professional Building Consultants in Prescott. He is a state-certified home inspector and has performed almost 5,000 home inspections in the Prescott area. West is past president of the Arizona Chapter of the American Society of Home Inspectors (ASHI), and currently serves on the Home Inspector Rules and Standards Committee for the Arizona Board of Technical Registration. Contact him at

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