Clean out your ductwork if it s confirmed that you have mold growing inside.
Black spots flexible ducts attic.
Use metal flex or fiber board ducts that are insulated to.
Confirm that the black particles are actually mold spores through a lab test.
Dark dust is blowing into your home.
The sun would come out melt some ice and it would find it s way to the nearest hole into the house.
Your home s ductwork is located in unconditioned spaces like attics and behind walls where all kinds of dust and dirty insulation abounds.
The last usual cause for condensation on a duct system is if the ducts are not properly hung or they are touching each other.
Ductwork located in an attic must be hung properly so that the insulation can do its job.
When ductwork is touching it forms a very cold spot where they are touching thus condensation begins.
Black dust around air vents.
If the register is closed the air is forced along the ceiling and the next thing you know you ll start to see black buildup across your ceiling.
Black mold has a distinctive unpleasant musty smell.
The flex ducts were literally filled shut with ice in the low spots compressing the scant insulation layer beneath them.
Install ductwork so that it is in direct contact with i e laying on the ceiling and or truss lower cords.
If you notice black dust around your air vents this could be a sign of black mold growing within.
Most of the time dirt accumulates on ceilings because air is leaking in from the attic between the drywall and the supply register.
When hvac ducts are installed in a vented attic in a dry climate bury the ducts in attic insulation to protect them from temperature extremes in the unconditioned attic space.