The drawbacks of unvented gas heat

Kevin Brady

I really need to re-think this whole garage shop heating thing. I have a propane heater - one of those 80,000 BTU "Reddy Heater" units, fed by a 100lb. propane tank. It provides more than enough heat for my attached, 2-car garage shop. The downside is that it generates huge amounts of water vapor. About 1.63 pounds of it for every pound of propane used, by my calculations. At 80,000 BTU, it burns almost 4 lbs per hour, so that puts about 3 quarts of water into the air each hour. Having the door open a bit for ventilation doesn't alleviate much of this moisture.

The trouble with this, is that water condenses on everything in sight. I run fans to keep air moving, but that only partially reduces the problem. If my tool surfaces are below the dewpoint, moisture will condense on them. Last weekend was a particularly chilly one, and my garage was in the low teens. That meant raising the temp some 40 degrees or so to get it reasonably comfortable. Since the garage is only lightly insulated, I had to run that heater at full throttle all the time. It felt like a rain forest in there. I was scrambling to wipe down cast iron surfaces before rust set in.

I must seriously consider alternative means of heating the shop. Perhaps one of those vented garage heaters, like the "Hot Dawg," would do. I have considered electric heat, and based on the electric rates here, that would actually be cheaper per BTU than propane. But 240V electric garage heaters for consumer use tend to be limited to around 4000W, which converts to roughly 14,000 BTU - a bit anemic for a 450 square foot garage.

Natural gas would be cheaper yet, and my furnace room is just on the other side of the garage's back wall, so running pipe from there wouldn't be too involved. I have been considering building a separate shed in the yard for WW, but those plans are up in the air. So for now, the garage is it.

In any case, I'm leaning toward a vented gas heater. Anyone have some good ideas and tips for these? How involved is the installation for a DIY setup? I'd appreciate any thoughts on this. Thanks!


Last edited:

Rennie Heuer

Staff member
Constantine, MI
Hi Kevin,

I have the Hot Dawg and could not be more pleased with it. We keep the garage/shop/laundry at about 50* all the time and turn it up to 65 when I go out to work for a while. Usually takes about 20 min to get toasty.

I hung mine from u-channel (I think that's the correct name). I had a friend that works for the local gas company plumb it for me and then called in a professional HVAC contractor to vent it through the roof.

Our winters are mild in comparison to yours - though we have had many mornings this winter with temps below 15. Insulation in my shop is standard fiberglass batt in 2 x 4 walls. I put 8" above the garage (attic space).
DSCN0945s.JPG DSCN0946s.JPG DSCN0947.jpg DSCN0944s.JPG

hope this helps.
Last edited: