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Unvented Natural Gas Space Heaters Should Be Removed

Unvented Natural Gas Space Heater Produces Moisture

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.

Yes, carbon monoxide inside the home is certainly a danger, and that’s the best reason to get rid of unvented gas space heaters. It’s just never a good idea to burn a fuel inside your home without having a vent for the combustion gases.

Carbon monoxide results from incomplete combustion of natural gas. During complete combustion, natural gas, which is mostly methane (CH4), 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.

The often unrecognized problem with these heaters, though, is the huge amount of water vapor that they 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.

About 5 or 6 years ago, I got a call unvented natural gas space heater water vapor combustion safetyfrom 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 the storm door had so much condensation on the inside of the glass that it was dripping down. Inside the house, microbial infestations were growing on the walls and ceiling in the back bedrooms. (I wish I’d taken a photo of that door but unfortunately didn’t think to do that.)

The problem was that she was heating the whole house, which was probably only 1000 square feet or so, with two unvented natural gas space heaters. Because the house was poorly insulated and air sealed, there were plenty of condensing 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), the spores, which are everywhere, will activate.

If you – or your grandmother – have unvented natural gas space heaters, get rid of them right away. They’re not good for homes, even when they’re operating perfectly.


Photo by warrenski from

This Post Has 7 Comments

  1. My aunt in south Georgia had
    My aunt in south Georgia had one of these in every room, exactly like the one you’ve pictured, and they were in use for decades. She’s gone now and the house was remodeled years ago. Not sure what the owners did with them. Its unnerving to think how little we’ve understood how heating systems, ventilation, insulation, combustion safety, etc., actually ought to work, and for so many years. But good thing that we have people like yourself finally explicating the science behind the practice and getting the word out on proper practices and safety. So thank you, Allison!

  2. I would assume the same would
    I would assume the same would be true for these non-vented gas fireplaces. Yeah the salesman says it’s safe, but is it really?

  3. John, unnerving yes, but
    John, unnerving yes, but understandable, too. We’ve had open fires in our homes since the days when we lived in caves. The problems with this have crept up on us in recent times as we tightened up and insulated our homes and switched to more hydrogen rich fuels. But we know what to do now, so it’s time to get rid of unvented combustion inside the building envelope. 
    Josh, yes, the same holds for unvented gas fireplaces. They’re banned in some green building programs and should be banned by code, too.

  4. Many years ago, my husband
    Many years ago, my husband installed 2 gas space heaters which had, apparently, belonged to his dad, in our home. They are hooked up to the gas line. He is too ill now to maintain them, and I don’t feel safe using them. Who can I call to remove them?

  5. In regards to the unvented
    In regards to the unvented gas fireplaces….is there another option? We have this installed but not in an original fireplace. We need an alternative heat source.  
    Thank you.

  6. I installed a ventless
    I installed a ventless natural gas space heater with ODS three years ago and have had none of the problems you suggest. We moved into a home with a furnace old enough to still have a pilot light and went through filters like they were toilet paper. Now it runs half as much which not only saves us money on heat (ventless is 99.9% efficient), but we no longer need to continuously fill and run two portable humidifiers that we did before. Those who follow the directions which disclose the humidity issue as why these are NOT to be the primary heat source for a home should have no problem. The balance between the furnace and space heater is easy enough to adjust.

  7. my unvented space heater is
    my unvented space heater is producing a smell like propane gas. It is several years old and in used regularly and often in the winter. Why does it produce a propane gas odor now when it didn’t before?

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