View Full Version : Combustion air vents

John Stephenson
06-01-2007, 01:43 PM

Eric Barker
06-01-2007, 06:33 PM
Not sure that the vents do much. Compared to the air that a fire requires, the vents are not that useful. I do not comment on their absence.

Bob Harper
06-01-2007, 07:30 PM
There have been some good studies on the efficacy on passive combustion air intakes. Take for example your typical 4" vent using aluminum flex hose with one broad radius turn to a listed inlet termination about 3 ft. away. With a 5 Pascal pressure gradient and still wind, you may get 10-12 cubic feet of air per minute through this kit. Meanwhile, 400-600 CFM is being sucked up the fireplace. Now, let a 10-15 mfh wind attack the other side of the house so this kit is in the leeward and it may act as an exhaust sucking heat, smoke and gases out of the Fp. Why else would the codes require a 1" clearance off air kits on masonry Fps?

Dale Feb has a movie of a vent spewing flames with wind gusts. Yes, these kits not only won't do much to help the Fp but could actually contribute to a fire. The codes are not retroactive on their inclusion. Current codes do require them. What the code does not require is for the homeowner to use them! I have demonstrated air kits actually causing smoking to homeowners.

Fix the house and the Fp will work.