OK, you were all correct. The mystery door was a chimney cleanout.
These days, the flue for a gas furnace goes up that chimney. The door itself is badly corroded and is allowing moisture to produce mold on the basement wall.
So ... what is the 'Wreckommendation here? There really isn't a reason to get back there. Can it just be covered up with a metal plate caulked to the wall? Bricked in? Or does it really need to be replaced as it was?
I would put in a clean out door if the chimney is open at the top, by the time it needs to be replace the chimney will probably need to be tuck pointed. If the chimney is not lined the exhaust from the furnace is acidic and will eat the mortar. Yes the fun of home ownership.
If that chimney is still in use, I believe it needs a cleanout. When I had the furnace in a previous house converted from oil to gas, the gas company insisted that it have a cleanout (it should have had one all along).
I'm pretty sure that this was brought in the previous thread:
The moisture may mean that water is getting into the chimney. I would suggest getting a chimney expert out to have a look.
If it's not rain, it could be condensation caused by the flue, which is also not a good thing.
Covering it up will certainly solve one problem: you won't see the mold. Out of sight, out of mind...until it gets really bad. Covering it would
*not* be something that I would suggest.
I ASS U ME the gas "flue" is a stainless steel liner? If so it NEEDS to have a cap on the top to keep water from getting into the original masonary flue, as well as keeping water out of the stainless flue. Side effect of keeping critters out of the chimney. Mine has a seal around the stainless vent in the clay flue, with a metal cap over it with about 6 inches of expanded metal "screen" all the way around. The metal "roof" sits about 6 inches above the chimney top.
Is there a cap? If not you may still need a cleanout to get out squirrels or birds. I'd replace it and cap the chimney.
There _should be_ a cap on the chimney when the flue for the gas furnace was installed.
Otherwise, just 'seal' the clean out door. plastic/metal/ cement-board, brick, tile, your brother-in-law cask of amaretto. Caulk/ "plaster" well, and ignore it.
Perhaps there should be a cap but I can show you tens of thousands of houses that don't have them
As for sealing the cleanout, sure, but seal it with the idea it may have to be opened.
Best bet is ask the building inspection department whether it is needed for comply with code.
How many people have thought "no big deal" - until something went "wrong"? Like the chimney which starts halfway up the wall in the kitchen?
Yeah, Maybe bricking your brother in law in with a cask of Amaretto might be a bad idea.
Code does not matter if a squirrel gets down there. Accessibility does.
If a squirrel is a problem use a blood thinner.
...
Or a pair of barn owls decide to raise a brood at the bottom...may need earplugs as well...
One way to learn the varmint cover has gotten blown off in a storm; not recommended as the "first choice" one, however.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.