New answers tagged ventilation
B-vent is what should be used for exhausting gas appliances and most likely why you have a gap in a 6" escussion with a 6" pipe in it. Notice the ID and OD for B-vent. If its just an air handler for a bath fan use a flapper vent. AMPG's PDF Now you can fill the new 1/8~1/4" gap with an approved high temp caulk.
I'd pack it carefully with rock wool or fiberglass batting. DO NOT permit the two dissimilar metals to contact each other where there's any chance of moisture getting into the contact area, or you'll get galvanic corrosion at the junction, which can lead to leakage and exhaust gases getting back into the structure.
If my understanding is correct, you are referring to the knee wall formed when you finished the attic. This is a pain in the butt to vent; join the club. I have a caped cod which has the same issues. You need to vent the knee wall to the main attic above (the peak) while not loosing the insulating properties for the rafter space in the sloped area. I ...
If that grate-covered hole is in a "common area" and up against a wall, you can bet that it was once a floor furnace. The combustion boxes on older gas floor furnaces would crack over time (decades) and become a carbon monoxide (CO) danger to inhabitants due to flue gas escaping into the home instead of going up and out the vent pipe. A utility inspector ...
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