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Exterior Combustion Air Passageway Size

mossman's Avatar

Join Date: Mar 2009
Posts: 3,258

08-29-17, 07:02 AM   #1  
Exterior Combustion Air Passageway Size

I am having an addition built and the chimney will be enclosed. Therefore, the air intake passage will need to be extended to the outside wall of the addition. This will be done with PVC pipe run down the face of the chimney, under a structural slab, and out the side of the new foundation wall. According to the IRC, the passageway for supplying external combustion air for a fireplace is 6 square inches minimum and 55 square inches maximum. The existing passageway is about 6" wide x 3" tall and rectangular (brick-lined passage). 6 square inches is about equivalent to a 1.5" I.D. pipe. This seems awful small to provide sufficient combustion air. We'll likely end up going with a 2" or 3" pipe regardless, but I'd like to know that I am interpreting the code properly. And is PVC pipe and acceptable conduit for providing combustion air to a wood fireplace? Not a stove, but an open wood burning firebox. Again, the pipe will begin on the exterior of the chimney, about two feet downstream of the firebox.

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