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How to join B-vent and single wall pipe?

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Local code now requires 4" heater vent with any new water heater--I have 3".  With a new 36K BTU heater I want to change old double wall 6x6x3 wye--in same room as heater and 1 foot from concrete wall-- to single wall  6x6x4 wye.  The old wye looks like a plumber made it on-site because the 3" branch is single wall!  ( The other branch goes to furnace).  

How is the transition made between single and double wall vent pipe?  Is there an adapter that I haven't been able to find for this, or will the new single wall wye male end fit right inside the B-vent pipe female end.  If so, I would secure together with 3 metal screws long enough to go thru both pipes?

 Thanks for your advice.

Ted Sterne
asked in Gas Water Heater by tdsterne (120 points)
edited by darekrudy
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1 Answer

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Hi Ted,

Yes, sometimes plumbers or HVAC guys manufacture those vent connectors on-site. There are no screws permitted on double wall vent pipe connections (unless its locking design calls for a screw) except for the first connection with a single wall vent pipe, which is very common (pictures below).

Single wall vent pipe should fit into the inner tube of the double wall vent pipe. You can use longer sheet metal screw and penetrate three walls or (that would depend on the B-Vent lock design) open / bend 3 locks on the outer wall (visible on the bottom picture / next to the screw) and drive the 3 screws into the formed openings / through the inner B-Vent and a single wall vent pipe.

Let me know if there's anything elese I can help you with.

Thanks

Single wall "Y" connected to a double wall  B-Vent pipe.JPG

Single wall vent pipe connected to a double wall B-Vent pipe with screws (3 required).JPG

answered by darekrudy (21,730 points)
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