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Ventless propane heaters in crawl space

I just looked at a residential repair job (replacing leaking skylights) and the homeowner showed me some work that was recently completed in their crawlspace. A contractor had installed two ventless propane heaters in an uninsulated crawl space to supposedly save energy!

It is a second home with electric resistance heat at over 5,000 feet in the North Carolina mountains. The crawl space has an incomplete vapor barrier, sealed vents and obvious moisture problems with mold and non PT sill plates starting to rot.

The homeowner was pleased with reduction in electricity for heating. I have not yet asked if they know what their increase in propane has been. I would like to explain how a better solution will be to encapsulate the crawl space, seal the floor plane and realign and replace missing insulation. I would then recommend putting a vented heater in the conditioned space.

I would also like to explain that the addition of these heaters will worsen the moisture problems in the crawl space. Does anyone have any figures on how much moisture these heaters put out in relation to fuel consumed? I would also appreciate input from professionals here on how you deal explaining this type of information to homeowners without making them feel stupid. They just paid a good deal of money to a contractor that they think highly of and thought solved their problem. Seeing this type work by so called professional contractors never ceases to amaze me.

Travis Thompson
T-Square Builders Inc.

Asked by Travis Thompson
Posted Sep 25, 2010 12:20 PM ET
Edited Jan 22, 2013 2:07 PM ET


11 Answers

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Combustion of propane will produce about 1 gallon of water for every 5.6 gallons of propane consumed.

To convince a homeowner of a better way to do something is not a matter of avoiding making them feel stupid but of making yourself appear knowledgeable and competent. There is no substitute for that.

Answered by Riversong
Posted Sep 25, 2010 1:22 PM ET


And don't forget to sell him on replacing the sills before you seal the crawlspace (he's going to love that), or you won't be doing him much more of a favor than the last guy.

Answered by Riversong
Posted Sep 25, 2010 1:24 PM ET


Why didn't the owner hire the other guy to do the skylights, since he did such a competent job in the crawl space?

Seriously, does this guy not understand that he is burning gas in his crawl space without venting, and that CO is released when gas is burned? A claim I heard recently, by someone who has done tracer gas studies, is that roughly 35% of the air in your house came in via the crawl space.

You need to explain the facts of life to this guy. Yes you will impugn the reputation of the other "contractor", but it sounds like he needs it.

Answered by David Meiland
Posted Sep 26, 2010 12:44 PM ET


Approach this as you are doing them a favor by bringing it to their attention, because you are. Approach it as you wouldn't feel right not bringing it up, because it sounds like that is also the case. As David and Robert mentioned, don't worry about the other contractor (just don't be too harsh) and you will come out looking much more experienced and knowledgable. Bad air (CO and moisture) entering the house should be reason enough for anyone. It sounds like the crawl space heaters are fairly recent so they probably haven't even begun to see the damage that will be done.
Good luck!

BTW- it's good to see someone else from WNC on here!

Answered by Hunter Dendy
Posted Sep 26, 2010 12:56 PM ET


Thanks to all of you for the valuable info. I am going to send them a quote for the skylight work and then suggest we talk about my seroius concerns about the crawlspace issues. I have no idea why the previous contractor wouldn't have suggested a monitor type of heater in the living space instead of 2 unvented units in an uninsulated crawlspace.

Answered by Travis Thompson
Posted Sep 26, 2010 1:24 PM ET


Complete combustion of propane produces only CO2 and H2O. It's when it's oxygen-starved that a propane burner will put out CO.

Travis, to be kind to the previous contractor, at least he did seal up the crawlspace vents. He probably thought he'd be killing two birds with one strategy: drying the crawlspace and helping to heat the house. He just didn't understand that he was killing all the birds!

Answered by Riversong
Posted Sep 26, 2010 2:45 PM ET


Well put. We are in a very small and rural market with a deeply entrenched old boys' network. The contractor in question is very much one of those old boys. This type of situation arises frequently and I feel that there is a need to treat the situation delicately for all involved, while trying to insure that in the end things are done properly for the sake of the homeowners, the environemnt and our industry. Thanks again for all the thoughtful respones.

Answered by Travis Thompson
Posted Sep 26, 2010 4:12 PM ET


Complete combustion of propane produces only CO2 and H2O. It's when it's oxygen-starved that a propane burner will put out CO.

Right, but the only time I've seen 0ppm on my CO counter is when I'm outdoors and just turning the unit on. Even the best burner is going to have some CO. Cheap ventless burners in a sealed crawl... who knows, but it seems like a knucklehead idea to me.

Answered by David Meiland
Posted Sep 26, 2010 9:29 PM ET


Maybe it'll kill the rats?

Answered by Riversong
Posted Sep 26, 2010 9:53 PM ET


Or keep 'em warm. We had a cold snap a couple of winters ago (a heat wave by your standards?) and I ended up with a wiring harness under the hood of my truck chewed into bits. Apparently the rats are smart enough to wait until you're in the house, then they scurry up into the engine compartment and find a place to hang out, with something to chew on as an added bonus.

Answered by David Meiland
Posted Sep 26, 2010 10:45 PM ET



I opened a hood years ago when I worked as a kid at a Detroit-area service station and a possum that had been enjoying a warm nest on the back of the engine waddled out and put up a good cat a mouse game with the local police.

Answered by Riversong
Posted Sep 26, 2010 10:56 PM ET

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