This was a return plenum from last week. There were no filters and the filter was installed incorrectly at the furnace. The mold (I know because I tasted it ;)) was below the wood return that was full of holes.
Nasty stuff being circulated in this house.
Dirty as it is wood is allowed on the return side due to its temp no condensation
I know its allowed Charley, but I reported the fact that the moisture issues in the crawlspace had rotted through into the plenum and that the filter was doing them no good being sucked into the fan.
P.S. We need more posts like this on the board. Keeps us sharp 
Had this from yesterday some mental Giant had this brainstorm for his water heater vented horizional for about 10 feet to the exterior from the basement then up the side of the structure thru the roof I guess he thought the vent was ugly so he would hide it and make it pretty behind that flammable wood.
As soon as I got my back draft flame within about 3 inches of the vent intake it blew the flame out ya can see on the pic the nipple all corrioded from CO backdraft
What is the cure for this problem???
Have a power vented water heater installed.
I suggested a electric
couple of obs… (didn’t read thread yet)
Looks like a downflow… is that wood? If so, unless there’s some crafty way they used ductboard or something, that isn’t great on the supply side. I don’t gripe about return side. Also… as there are comb. appliances present, where is the return out of curiosity.
Does that plenum off to other ducts…?
Some condensate defects/recommendations as well… lack of visible secondary drain or some type of cut off / overflow switch (if it has one ported)
Oh well done W.A.G.'ing for now. I’ll read thread later.
