Hello everyone. I haven't been here for a while and have a new problem. Last spring we had the crawlspace ceiling of our beach house spray foamed, including the joists, with 2-3 inched of closed cell foam. Unfortunately, the AC still smells a bit moldy, though not as bad as before. I'm guessing that there is some growth inside the ducts, which are all flexible, not sheet metal. Can you tell me whether I can replace the ductwork then just re-foam in those areas. My worry is that the foam won't stick well to itself when reapplied. Thanks for any insight you can offer to help me correct this problem.

As far as I know, urethane foam sticks very well to itself.

A few hours a day of well dried (say < 50% relative humidity) air might be useful in killing mold in ducts. There will always be some dust in them so cleaning or replacing may be only a reduce, not fix solution.

Thanks, Jon. I think I may begin with dehumidifying the crawlspace. Not a perfect solution since I can't seal it completely (required by code to have flood vents...it's a beach house), but it helped before. This way I can at least see if the smell is coming from the ducts themselves or the crawl space air is still finding it's way into the house. Will have to wait till next spring to see if it makes a difference. In the meantime, maybe a winter's worth of warm, dry air through the ducting will help. I really dread the idea of replacing the duct work.

I'll say the same thing for a crawl space. Good dehumidification for a 4 hours per day will be much less expensive and may be just as effective against mold as 24 hours/day.

I see that there are flood vents that have doors but no grills. These plus the usual air sealing should help with air infiltration into the crawl space and make dehumidification effective and affordable.