Orphan water heaters

How do you evaluate and report on “orphan” water heaters?
What conditions will cause you to defer to a specialist?

One instance could be that when the furnace was removed, and not replaced, the venting above the old furnace connection is so large that the water heater exhaust cools and condenses into carbonic acid and is eating the flue pipe away.

Lets say the furnace is gone and the water heater is venting into the chimney by itself but the visible metal flue pipe is in good condition.
What would you report?

For how long was has it been orphaned? Has it been used on a consistent basis? Was it upsized, as far as BTU’s? Maybe conditions have yet not showed up yet?
Regardless, to answer your question, I’d report that the furnace has been removed and a high probability exists that the water heater BTU output may not be “warm”/ effective enough for ideal chimney function and may cause issues. A new separate metal chimney may have to be piped through the current liner to the top and capped off to rule out any of these potential issues. Of course, this is all way outside the scope of a general home inspection and validating this condition would involve invasive or specialty procedures. Unless the homeowner has documentation stating otherwise and/or that everything was accounted for when furnace was removed, have a qualified HVAC, plumbing, or chimney professional evaluate to determine if water heater and/or chimney is properly sized for effective/optimal, and most importantly, safe, operation.

Something like that…


If you didn’t want to read all of the above, this is what is needed.

“You either line the chimney or change the water heater to a sidewall-vented unit,” says Donadee. Lining the chimney usually requires the installation of a 3- or 4-inch diameter aluminum or stainless steel liner, all the way up to the chimney top."

Called flue liners, if it is a big masonry chimney use an insulated vent pipe like B vent.