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Old 05-15-2013, 04:51 PM   #1
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Use existing hole in house for venting

I have a house that recently had the kitchen remodeled maybe 1 year before I purchased it. The previous contractors left some of the old 6" galvanized steel stove vent pipe. This pipe still has the old cover and termination on the exterior wall on the house and is now filled with removable spungey foam and goes into the house maybe 2 or 3 feet and just ends.

I want to install a condensing tankless gas water heater which uses 3" PVC for intake and exhaust. I plan on using a Concentric Vent Kit so the pipe that would protrude through the exterior wall would be 4.5" (if I am not mistaken).
The water heater will be located very close to the existing old pipe mentioned above. I loathe the idea of having to cut a hole through an exterior wall when there is an unused one right there.

My question is does anyone have any ideas on how I can utilize the existing exterior hole? The problem is the new pipe is smaller than exterior hole by quite a bit (4.5" vs. 6"). I could easily remove the existing pipe or maybe even run the PCV piping through the galvanized pipe. I guess I need a way to make sure the space between the hole and the pipe can be made tight and sealed (is there such a thing as a 6" diameter venting kit that connects to 3" pvc pipe?).

Thank you very much in advance for any help!


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Old 05-15-2013, 05:33 PM   #2
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There may be.... but any metal/tinning shop can make it up for you....


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Old 05-15-2013, 06:57 PM   #3
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Most Manufacturer's Instructions provide minimums for vent intake and exhaust sizing and not maximums. So there shouldn't be any issue if you use a pipe bushing and increase the size of the pipe at it's termination to better fit the exhaust hole. They also make escutcheons of various sizes, or you could just cover the existing hole with some fascia board and drill an appropriately sized hole in that.
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Old 06-06-2013, 08:26 AM   #4
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Because it's a Concentric Vent Kit I don't think I can use a bushing and go to a 6" for the opening as this would allow mixing of exhaust with intake unless I am just not understanding how it could be done.
I think I will try to fabricate something for the exterior, either cover the hole with wood and allow a 4.5" hole or see about getting something made for me.

Thank you for the replies, they are appreciated!
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