The a/c vent in master closet is dripping with condensation on outside of vent. Packed insulation around top of vent in attic, to no avail. Any suggestions?

Could be the humidity in that room is high enough to reach the dew point on the grille when the conditioned air is pouring into the room. Most moisture from register boxes seeps onto sheetrock around, not from the register.

Is it metal or plastic? If metal, switch to plastic. Profit.

Might not hurt to get in the attic and check to make sure the duct hasn't come loose and isn't pulling in some humid attic air.

Packing insulation around the vent is like trying to stop a leak by tying a rag around the faucet. The air is under pressure coming out of the vent. This creates a low pressure area right around the vent. If there is a path (hole) for warm-moist air from the attic to be drawn in then it will instantly condense on the grill.

I would use foam to seal the boot to the sheetrock. If this does not fix it then the the warm-moist air must be coming from somewhere near the vent like a door that is constantly being opened.

If the master closet is off the master bath then see if shutting the closet door when showering/bathing effects it.

Is this the return or the supply?

How can air come INTO a supply duct if you have positive pressure? I can see a vacuum/injector set up with the intake and a small hole from the attic.


I would put money on the air in the room being humid and the conditioned air causing the temp to drop and liquefy water. Turn on the vent when you shower or for a short period to drop the humidity.

~egon

I'm thinking he's got a leak drawing outside air from the attic like a venturi. If it were bathroom air from the shower, the condensation should go away as soon as say the mirrors lose their fog.

If the condensation is dripping from the register, there is either a leak around the duct boot which the temperature differential from the attic and supply air is condensating or the there is a break in the supply duct and is condensating down the duct into the boot and onto the register. The humidity levels could also be a cause but is highly unlikely that this is the only cause in a master closet.

I am an HVAC company owner and we see this all the time in homes that have high ceilings in the master bathroom and adjacent master closets.

Hope this helps!

I have something similar in one room only and have begun to see some mold form.

I have this same problem in my main living area. I understood the AC unit to work to dehumidify the air, hence the confusion here. Since my AC is new, I will probably call my company and see what they say.

Mold growth present at Grils:
You need to check the area around the boot at the sheetrock. Seal the cracks around the boot under the grill with caulk or duct sealant. Also check the connection of the duct to the back of the boot for leakage.

The unit does dehumidify the air but that doesn't mean it will dehumidify to the level needed if you live in an extremely humid climate. You either have seal issues or a high level of humidity in the house from the unit not running long enough to thoroughly dehumidify the conditioned air.

I own an HVAC company and see this all the time in the Dallas market.

The unit now runs most of the time since its a 2 stage, and I have kept it pretty low (~70). I just can't figure out where all the humidity is coming from. We noticed this several weeks ago before it got real hot. Never had an issue like this, though the vent in the bathroom has a little rust on it. There, I can understand.

Getting a new roof, so may see if they can pipe a vent stack for a dehumidifier in the bathroom.

J Curtis,
How far north do you service?

same question for Jcurtis, how far north do you go?

I have 3 A/C vents in a cathedral ceiling master living room that get a minor drip during the summer years. From my understanding it is when the cold A/C air hits the warm (hot) humid air at the top of the cathedral ceiling, forming condensation and thus dripping.

I went up into the attic and it is SEALED well, there is no leakage of cold air from the A/C ducting to the back of the vents.

Looking at the vents themselves, there does not seem to be any "side leaks" or other issues.

Additional note, the condensation forms at the top of the grill, not the bottom, and the grill itself is metal.
I read on another site that maybe I should replace the metal (that gets pretty cold when the A/C is hitting it) with plastic.

Thoughts?

Thanks
-russ