Mold in A/C Registars

I had it in a bathroom. The problem is not with the air conditioner, it is that the bedroom air has too much humidity. Maybe start sleeping with the door open (once the conjugal visit is done)!

The mold at the AC register will be caused by moisture and this article will describe why the moisture forms, from a physics standpoint, and some some possible causes. Why Do AC Vents Sweat.

If it appears to be confined to the one master bedroom vent a common cause, but certainly not the only cause, is the AC register boot for that particular duct run in the attic is it is not properly sealed to the drywall where it enters the room and/or is not properly insulated - may need to be sealed from the attic side, sometimes can be sealed from the register (room side). Article to get you started Sealing Ducts to Floor or Drywall . Tons more articles/videos on the web.

quote:

---

Thanks, and we saw some surface mold on the popcorn ceiling there but there appears to be mold inside some of the other registers. Some background story is we replaced the very old AC and ductwork 3 years ago but I don’t recall the boots or registers being replaced so it’s been recommended that we replace and insulate the boots since the original aren’t insulated. That makes sense to me. What I have left to figure out is twofold: 1. Do I get the whole AC system cleaned? The mold may just be in the boots since it’s a relatively new system. 2. Should I look at replacing the sheetrock around the register in the master bedroom? I cleaned it a couple weeks ago and the mold hasn’t come back.

---

That additional information helps. If the boots are not insulated then that needs to be done. Personally I’m not sure I’d go to expense of replacing the boots if they are in good shape, that would be your call, but insulating-sealing them is a no-brainer.

Next question, do you really have mold or could it be mildew? There is a difference in regards to allergies, indoor air quality. If your new ducts that are 3 years old are flexible ducts, and not rigid, they can’t be cleaned. Perhaps the rigid boots can, but at that point it might be best to replace them - not sure. I’m no expert on duct cleaning, I have read a great deal on it, and I’d be reticent to take that route unless absolute necessary. It does sound to me, as you’ve described it, the problem likely confined to the boot area of your registers - that should not require entire HVAC duct cleaning.

Just keep an eye on and continue to treat the drywall with the proper chemicals if needed - once you resolve the moisture issue your problem should be resolved. There are those on this board more knowledgeable on mold remediation than me, hopefully they can provide better insight. Your duct registers-grills can be replaced or cleaned - that’s usually an inexpensive DYI job.