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 Tankless retrofit using existing chimney?
Author: ihatedrips (CA)

I have a small traditional water heater in my laundry room which I am thinking about upgrading to gas tankless.

I would like a non-condensing tankless unit because: 1. draining the acidic condensate would be a hassle; and 2. size

The old water heater has a B vent going up into the attic. I do not want to mess with this vent, because: 1. that part of the attic is extremely cramped and hard to work in; and 2. I have an old metal shingle roof which is hard to access and expensive to repair if I screw it up

When I look at the non-condensing options from Rinnai/Navien/Rheem they all seem to have a concentric 3/5 vent. But I want a two pipe solution: exhaust out the old B vent, and combustion air pulled through a separate pipe

Is this doable/common? Or does this pretty much always involve running a new concentric vent?

And also: if I buy one of the smaller 160,000 BTU units, is it typically mandatory to upgrade to a 1" gas line? Or only for long runs?

Redoing the gas + venting would make this project impractical for me. I want an easy upgrade.

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 Re: Tankless retrofit using existing chimney?
Author: bernabeu (SC)

It is NOT an easy upgrade.

fuh ged bout it


"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

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