Warning about whole house fans and improper airgap sealing between attic and house
Firstly, I'm a DIY homeowner, not an hvac guy. I responded today to this post...
https://www.reddit.com/r/hvacadvice/comments/1wxj8va/comment/pdu0dkx/
... and was shocked to see that nobody was diagnosing the problem.
Anything that is not sealed between attic and habitation space will act as a return channel and will suck the air and dust and fiberglass flying around the attic back into the house.
This includes any gap between ac ducting and sheetrock, any gap around or inside electrical boxes in the ceiling, same for extractor fans, any holes in the attic ducting, and also any airpath from the furnace cabinet to the house. Even electrical boxes in the wall can act as returns, especially if close to the fan and with unsealed holes through top plates for wiring.