Help on what this might be

Inspected a house yesterday and found this where the return air was in the wall. No elevated moisture located, is this mold or dust?



dust bunnies

Looks to me like at some time the dryer was vented into the open area in the wall.

Me too.

Not a dryer , unit has been run without a filter

Ths is dryer lint lol

I call them Dust Bunny’s too Michael. Always find this condition when minimum filtration is used in a home or in some cases nun at all.:shock:

I don’t agree with (me too) have you expericensed HI never looked behind a return air grill that had the filter located at the furnace the return air duct looks just like what is shown in the OP pic

I agree with charly.

Who is charly?