Black air filter

Any ideas on why this air filter would turn black within a week. The air handler was recently inspected by a licensed AC and given the thumbs up. The coils are a little damaged but were not dirty. FYI - this is in a first floor condominium. There was / is a problem with the tub leaking upstairs. Instead of correcting the problem, they just stopped using the tub. There has been no recent construction or any open areas where dust could come in. All of the walls and ceilings were checked with both a thermal imaging camera and moisture meter and everything came up dry. There is a cat and a dog in the home but there were no hairs on the filter or coils. Ideas are appreciated.

Hmmm…Chinese Drywall ??? :stuck_out_tongue: (Just kiddin’, maybe):smiley:

No, unit was built about 20 years ago. The only drywall that was changed in the the unit was the tub walls, and there are no other symptons.

Is the furnace oil fired?

Is the water heater in the same room?

Is it gas, etc? Is there soot rust on that burner? Does it ignite slowly?

This is Florida. There is no furnace. The water heater is located under the air handler. It is electric.

Perchance did you scratch it with a fingernail?
Did you smell it?
What did it seem like?

Stupidly I did not scratch it.
It did not have any smell
I did shake it, but nothing came out.

Is the garage attached?

You may want to check around that entry door and other places like this:,1055.0.html

There is no garage, this is a condo.

Around here condos have garages, mostly.

Oh, well, out of ideas for you. Good luck.

I know. Thanks.

Did you taste it?

Is it a washable filter? and how close to the salt water are you


Its a disposable filter.

Is the filter black to begin with? Are not carbon filters black?

no, they are white - bought at home depot probably

Replace it, and check everyday to see how fast it turns black. If happening the first day or so, and you/they can’t determine the reason, I’d send it to the lab to find out what the substance is. Can’t be good for the lungs. Imagine what made it through the filter.

David, yes, activated carbon filters are black. Naturalaire Flanders filters, as shown in the photo, do have an activated carbon version but it looks a little different than the one shown. William, did you say you saw new, clean white filters on site? If not, then you need to make sure these were not activated carbon versions.

I think you missed this one.