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Dale W. Feb · #9 (**permalink**) 06-16-2007, 04:13 PM

Jim,

I might not use the term “compromised” as it appears that everything is non-combustible and no fire will result unless you open the vent door. I would state that the hearth extension has been modified to accommodate a combustion air vent. I would then recommend that they provide an “air-tight” metallic vent duct from the vent inlet, through the basement area (the reason for the air-tight requirement) and out to the exterior. If this is not possible, then recommend abandonment of the vent inlet (remove and close).

As a general note, the location of this inlet is perfect for the operation of a fireplace system. The air enters the fireplace with an equal balance. We are identifying many poor locations as attached to this post. The back wall and part of the side walls of a fireplace are under positive pressure as the air moves into the firebox. The attached photos show the intake located at the rear wall of the firebox. The round aluminum air duct enters into the square metal slider sleeve without a transition or seal. There were three masonry fireplaces with “Class A” chimneys at this 30 million dollar residence. All three vents (outside of the firebox) where enclosed within a wood framed chase. I could see the framing and wall insulation on all three. We were very fortunate because of limited use. The outside combustion air vents are not normally considered a potential fire hazard. But as Bob and I have mentioned, they can be a real threat. These systems must be properly inspected to ensure our clients safety.

The photos depict the location of the air inlets and a view through the inspection mirror down to the aluminum air duct. The last photo shows the wood framed chase that surrounds the masonry fireplace, Class A chimney and aluminum air duct. The other two fireplaces were constructed on the interior of the dwelling.