By Paul Bianchina
Q: I recently purchased an unvented propane shop heater for my garage, which specifically said it was "ideal for use in a garage/workshop." The instructions say it must be used in a vented environment. I called the manufacturer, and was told to "just leave the garage door open a few inches," which would obviously make it impossible to heat the garage. Did I get some bum information?
-Charlie T.
A: Burning natural gas or propane requires oxygen, and during the combustion process, air is drawn from the room for use in the heater. This air needs to be replaced or the room will become dangerously depleted of oxygen, so makeup air is always a consideration with the installation of any fuel-fired heater.
Makeup air can come from different sources. If the garage is large enough, a sufficient amount of air is present to fuel the combustion process without causing any safety concerns. In smaller garages, it may be necessary to install a small outside air intake vent in the wall to provide the needed air.
The other consideration is venting. Unvented heaters sold specifically for use in enclosed rooms typically do not produce waste products in sufficient quantity to be a health hazard, or they could not be sold for use indoors. However, venting may be the reason the manufacturer is telling you leave the door open.
Either way, I think the manufacturer did you a real disservice by simply telling you to keep your garage door open a few inches. This is obviously not a practical solution, and in my opinion is providing considerably more air than is necessary for either combustion or venting.
All that being said, you need to follow the manufacturer's specific instructions. I would suggest that you call the manufacturer one more time, ask to speak to someone in their technical or service department, and run that question by them again. If this is the best advice they can offer, I would return the heater and purchase one from another manufacturer that can provide you with more specific details that are pertinent to that particular heater. You can also get more information on venting and makeup air requirements from your local building officials.
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