10 water heaters on a trunk

10 water heaters venting into a main trunk that then transitions into a regular b-vent that terminates through the roof. There is a pitch to the trunk. Not sure what to say about this, seems problematic and I’d expect condensate to rot it out in the near future but not sure what to specifically say as I’ve never come across this quantity of units and maybe this is normal?! (its actually two separate areas each with about 10 water heaters each). Thoughts?

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What are these units serving?
I’ve inspected 100 room Hotels that only use three or four 100 Gal WH’s.


Not something I had ever seen. I can dream up all type of potential problems but that does not make it wrong. Honestly, I do not see how it could draft consistently.

Is this dinosaur connected to the same system flue system?



no its no in use anymore, all electric heat now

20 unit apartment with separate utilities

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I see a few other problems. But, as far as design of that exhaust system, it would need to be engineered IMO and may have been

Problem below (not the tree trunk) I see negative slope on that flue


Hole and lack of fasteners


I get these trunk setups pretty often, but 5 is the highest number I’ve seen on a trunk. They don’t make me feel comfortable, but some of them have been in service for a long time…

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I would write it up, to me it looks like they modified an HVAC air manifold duct to serve as a vent.

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Morning, Scott. Hope this post finds you well.

Multi gas fired appliance venting to a common flue manifold.
Imagine the amount of combustible air required for 10 gas fired water heaters.

I could be wrong but, I can think of any number of safety issues evolving from this type of setup.

Refer to a licensed gas fire appliance technician for further review.

Just my 2 cents.

I don’t see any way to maintain a draft and the backdrafting possibilities are endless. Each of these WH will fire at different times, depending on what combination is fired at any one time you could kill any draft completely. Write it up as poor draft and possible backdrafting and recommend further evaluation.