Furnace Staining

Not sure what to call this. Anybody know what this is? There was a water heater gas flue above it that was back pitched, rusted, had some holes in it. Was wondering if maybe that caused this somehow?

More pitting, rust and corrosion. It appears to be in a crawlspace. I suspect there were more moisture issues in the crawl as well.

1 Like

There are always moisture issues here 90% of the time. I kid you not. Does this need further evaluation or repair?

Yes it does IMO. But the problem may be more about the crawl environment than the actual air handler.

You can connect the two in your narrative. Elevated moisture in the crawl appears to be causing moisture issues to other building systems such as, HVAC rust/corrosion, floor structure fungal growth etc etc.

Edit: That flue may also be effected and is rapidly approaching a safety concern if not already. Also, flue rust may also indicate a draft problem separate from the crawl environment. That’s my 2 cents.

1 Like

Yes the flue is definitely unsafe in my opinion. It runs like 20 feet horizontally and is back pitched then goes up past the roof from the exterior another 10 feet. Very inefficiently ran considering the water heater is like 6 feet from the other wall. Also, I’ve never seen a water heater in a crawlspace before. There was nothing written on the water heater labeling itself to say it couldn’t. Most of our crawlspaces are only like 3 feet tall. This one was like a cellar.

Not a problem as long as it has combustible air and exhaust venting. If it is a vented crawl, then there is likely no combustible air issue.

1 Like

Also mention the wrong size filter with missing filter holder cover.
That’s sucking nasty crawl air into the rest of the house, maybe a lot maybe a little. (My service fee for some jobs includes replacing filters: I’d stick a smaller filter in and gob it up with tape if pressed and unable to find the proper cover).


Yes I agree. That’s one of the many reasons I don’t like crawlspaces for furnaces.

1 Like