Black Particles from a/c

I did an inspection the other day and found black foam like particles on the floor that appeared to come from the a/c vents. Any ideas on what this would be?

There is ripped duct work?

A pic would help!
How old is the unit?
What kind of heater, gas/elect or HP?

I ran into that also, It turned out to be that the vents had a small piece of foam around the flange to seal it to the ceiling. Over time[15 years] the foam was falling apart and would crumble when you touch it. I think most of it was caused by dust and the fact that the people smoked. When the ac unit was running the seal was loose and air would seep back into the attic around the vent.

Sorry so long to respond. The unit is an electric heat pump system. 3 Ton. The home is only about 3 years old. There was no other unusual factors present. When I did the inspection, there was no particles or black soot like material. This has occurred about three weeks after I did the inspection. The people were present at the inspection and agreed that this was not present when we did the job. I just would like to try and direct them. I offered to go back and look at it with them again to see if there is anything else going on now. Since the home is relatively new, I really do not know what this could be from.


Did someone check the filter?

First place that was checked.

I thought that was most likely the case. I would try to get access to the evaporator coil and see if there is any accululation on the fins. You may also want to consider duct cleaning. Is there an chance that the old filter was a washable type that had deteriorated?

Probably the best thing is to have an HVAC specialist come in and service the equipment/system (assuming that hasn’t been done recently) and check out the situation while they are there. It may or may not be from the HVAC system, and there is no reason to just guess.


If this definitely came from the registers and you checked the filter, then the ducts are dirty somewhere. Simply recommend HVAC evaluate and estimate repairs.

If you ran the heater coils, a summers worth of lint and dirt that bypasses the filters will burn and flake off. This may be some of the crud from that.

Last winter a lady called me and said there was black soot all over her new house when she gets home from work every day. This had went on for a week or so. I opened up the furnace and found reddish brown dust in the blower cabinet and black material in the wood grains of the rafter and ceiling joists (none on sheeting). Tape samples concluded the furnace dust was Aspergillus and the attic had Stachybotrys. Air samples also showed them in the living areas of the home. The concentration was so heavy, I had to retake them at a lot lower flow rate because they was compacting my air traps and the Industrial Hygienist could not tell what they were. Later I found out that the builder had the framing exposed for several months, this explained the mold on the rafters and not on the sheeting. Strange but true.