Vent pipe gap: OK to seal?


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Old 07-19-20, 03:36 PM
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Vent pipe gap: OK to seal?

The gas hot water heater in our 25-year old house is located in an upstairs vented closet. To help out our overtaxed HVAC I'm currently trying to identify and seal leaks from the attic, e.g. attic access door, recessed light cans, etc. When I duck my head in the water heater closet I definitely feel a pocket of heat & humidity that I'm pretty sure is at least partially due to air that has been drawn-in from the attic through the gap around the stove pipe as it passes up through the square sheet metal plate in the ceiling. (The HVAC return port is in the ceiling right in front of this closet door.)

Is there any reason I shouldn't seal this gap with foil duct tape?






 
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Old 07-19-20, 09:28 PM
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Since it appears that the vent goes thru a flammable area it should be B type vent.
That would be a double insulated type of flue pipe.
How hot does that pipe actually get ?
I'm thinking you may be able to use foil tape to seal it if it's not too hot.

Keep in mind in your sealing efforts..... the water heater needs fresh air to burn and exhaust the hot flue gases outside. You don't want to starve it for air.
 
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Old 07-20-20, 11:09 AM
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Thanks. Yeah, the top portion does appear to be B-vent. Air intake is at the bottom of the water heater, then at the top there's a cone-shaped draft hood that's partially obscured in the photo due to the angle. Attached to the top of the draft hood there's a short piece of single wall vent pipe that goes up into that couple of feet of double wall vent before going through the ceiling sheet metal plate.

I've only checked once so far, but my IR temp sensor measured only about 109 degrees at the top of the B-vent at the completion of one water heating cycle.

This morning I sealed the gap up with the foil tape I have (Polyken 360). Can't really tell yet if it's going to make much of a difference.
 
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Old 07-20-20, 01:30 PM
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Does the closet door have a louver in it so the water heater can get makeup air from the rest of the house interior for its bottom intake as its exhaust gases go up the flue pipe above? In this case the door louver should be low, as far from the HVAC return port as possible.
Still better would be a louver in the closet wall to the outside (if applicable and possible) so the water heater gets combustion air directly from the outside instead of use up heated or air conditioned air from the interior.
 
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Old 07-20-20, 02:00 PM
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The air supply come from the top of a stairwell through a two 12" x 12" louvered vents in the side wall of the closet. The vents are stacked with one even with the bottom of the tank and the other roughly even with the top, so I suppose in theory there should be a convection current drawing air out of the stairwell and feeding back into it. The flue draft was working the last time I checked it a long time ago, and I do have a new CO-2 detector only feet away just in case. At any rate, I agree it would be better if air could be drawn from outside, but it isn't really practical in this situation..
 
 

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