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Question DetailsAsked on 6/17/2014

do i need to have a new liner installed in my chimney before a new water heater?

I have a new energy saving furnace. When the plumber came to give me an estimate on a new water heater,
he said that it would be an "orphan appliance" and i would need to have a new liner in my chimney in order to have a water heater pass inspection. please tell me about this and about how much such a service should cost.

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1 Answer


Common issue when you go with a high-efficiency condensing furnace, so furnace now vents out the wall instead of up the original flue.

Depends on the Btu rating of the orphan appliance - there are tables in the UPC and elsewhere like on duct manufacturer websites on what size duct you need for certain Btu outputs for each fuel type. Sometimes orphan furnace is fine if you remove the water heater source, but generally remove furnace and the water heater does not produce enough heat to prevent condensing the water vapor in the flue, and does not have enough heat to ensure good convective flow up the flue so you can get excessive back-drafting, or with a long flue and on cold days even total flue gas stagnation so flue gases come out the draft hood right at the top of the water heater rather than going up the flue risking carbon monoxide posisoning, so good reason for the flue size requirement.

Unless you have a nasty set of bends (like with most very old, and especially 3 story and higher chimney flues) generally you can run new duct up the inside of the old flue duct without removing it, but some code areas require a firestop at each floor regardless of whether in another flue or not, so that can require total tearout and new flue from scratch.

Common cost - $300-500 for sleeving smaller one inside existing ducting, to $500-1000 range commonly if needs total reline - even more if was multi-hearth fireplace with lots of bends as you go up, and REALLY nasty in that case if old hearths have been bricked in so you cannot access middle of run to run ducting. In that case, common to go with pricier double-wall flexible stainless steel ducting (if allowed in your area), or to install flue-draft blower and new outside exit through wall rather than mess with trying to snake through sinuous chimney.

Answered 5 years ago by LCD

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