My grandparents in Louisiana heated their home with natural gas space heaters in all the rooms of their home. I loved them because fires are just so fun! (I’m not going to tell you about that time my friend Bubba and I caught a field on fire, and the fire department had to come and put it out. Nor will I tell you about the fire that the two of us set in my mom’s clothes dryer. That’s really not relevant to this story at all.)
These atmospheric combustion appliances do create problems in homes from a building science perspective, but they don’t have the same type of problems that I wrote about with atmospheric combustion furnaces and water heaters a couple of weeks ago. The major problem is one that most people may not even recognize.
Beware of carbon monoxide
Carbon monoxide inside the home is certainly a danger, and that may be the best reason to get rid of unvented gas space heaters. Even if there’s no carbon monoxide, though, it’s just never a good idea to burn a fuel inside your home and leave all the exhaust gases in your home’s air.
Carbon monoxide results from incomplete combustion of natural gas. During complete combustion, natural gas combines with oxygen (O2) from the air and produces carbon dioxide (CO2) and water vapor (H2O). When the combustion process isn’t complete, you get more carbon monoxide (CO) and less carbon dioxide. With any kind of combustion in the home, you should have a low-level carbon monoxide monitor. (TruTech Tools sells two different low-level CO monitors*, both good.)
But CO isn’t the only problem
The often unrecognized problem with these heaters, though, is the huge amount of water vapor they can put in your home’s air. In my grandparents’ home, I think the gas space heaters worked well most of the time and didn’t produce much CO. They did produce a lot of water vapor, however.
Back when I was a home performance contractor, I got a call from someone who wanted me to come look at his grandmother’s home. I knew as soon as I walked up to the front porch that they had a big problem. They had the front door open, and condensation was dripping down the inside of the glass storm door. I found microbial growth on the walls and ceiling in the back bedrooms.
The problem was that she was heating the whole house, which was probably only 1,000 square feet or so, with two unvented natural gas space heaters. Because the house was poorly insulated and air sealed, there were plenty of cool surfaces for that water vapor, the front door being the most obvious. When you put water in materials that act as food (the paper on drywall, for example), mold spores will activate.
If you—or your grandmother—have unvented natural gas space heaters, the best thing to do is not use them if you have another source of heat. If you don’t have another source of heat, it’s best to start your search for a replacement right away. This also applies to ventless gas fireplaces. Unvented combustion isn’t good for a home’s indoor air quality, durability, or safety. And that’s even when they’re operating perfectly.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He is also writing a book on building science. You can follow him on Twitter at @EnergyVanguard.
* This is a TruTech Tools affiliate link. You pay the same price you would pay normally, but Energy Vanguard may make a small commission if you buy after using the link.
Photo of blue flame by warrenski from flickr.com.
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