Help!!! My basement ductwork sweating/finished basement!!

[Billbill84]

Freaking out! I have a fully finished basement and today I realized my furnace duct work is sweating in some spots (see photos). Just bought the house this past January so it's our first summer in this place. What's going on here?!?! Outside temp is a rather humid 78 degrees night time and my basement dehumidifier is showing a current indoor humidity of 50% which should be ok right? Basement isn't too cold either. What should I do? For all I know that duct work may be sweating above the drywall too!! Advice PLEASE!!!

 

[bud16415]

Is the humidity 50% or is that what it is set at? Are you getting a lot of water per day out of the dehumidifier?


Running the air conditioner hard will chill the ducts and condense water where the ductwork is not insulated.

 

[Fireguy5674]

The finished basement should be conditioned air so there should not be a huge difference in the water vapor content of the air to cause such sweating. Is there a significant source of water vapor coming into the basement from a drier etc. that would be causing excess moisture to be in the air? Are the vents supplying air to the basement closed off? I realize it is a basement and therefore subject to ground moisture invasion, but the air conditioner is a huge dehumidifier. Is the drain line for the air conditioner flowing water freely, IE not plugged? If the pan under the coil is holding water, the blower could be redistributing that water back into the duct system. Although it is hard to tell, it does not appear that that the duct work is stained or discolored so this may not have been a problem before. If this is correct, it says to me there is some difference in your operation of the system than the previous owner. Look for a reason there is more water vapor available than in the past.

 

[Billbill84]

The finished basement should be conditioned air so there should not be a huge difference in the water vapor content of the air to cause such sweating. Is there a significant source of water vapor coming into the basement from a drier etc. that would be causing excess moisture to be in the air? Are the vents supplying air to the basement closed off? I realize it is a basement and therefore subject to ground moisture invasion, but the air conditioner is a huge dehumidifier. Is the drain line for the air conditioner flowing water freely, IE not plugged? If the pan under the coil is holding water, the blower could be redistributing that water back into the duct system. Although it is hard to tell, it does not appear that that the duct work is stained or discolored so this may not have been a problem before. If this is correct, it says to me there is some difference in your operation of the system than the previous owner. Look for a reason there is more water vapor available than in the past.

Is the humidity 50% or is that what it is set at? Are you getting a lot of water per day out of the dehumidifier?


Running the air conditioner hard will chill the ducts and condense water where the ductwork is not insulated.

Hi thx for your response. I have the 70 pt dehumidifier set to 45% but it will usually take a full day of running, apx 12-16 hrs to max fill up the tank. By the time tank is full dehumidifier will read usually about 50%. I know it's not going to actually hit 45% because it's a single unit working in a 1300sqft basement. The sweating was only visible around the top supply duct above the furnace where the cool air supplied to main level and upstairs. And sweating was found on the other supply as shown in the pics. I did not see or feel any sweating in any of the actual vents in basement or rest of house. Should note that my actual furnace room where I found the sweating is in its own room and the door was closed. In addition to that, I had all ceiling vents in basement closed because last winter I was trying to push more warm air to our upstairs 2nd story. Since I opened every vent in house including all basement ceiling vents and left the furnace room door open, ducts are cool but there's hasn't been any sweating yet and A/C been on all day. It's 92* daytime here right now so we'll see what happens at night when humidity is higher outside. I did notice that second story (feed by insulated flex duct in attic) is hot upstairs but that may be another issue. Thoughts on all this??

 

[Billbill84]

Update: as I stated above, the sweating on the duct has stopped after I left the door to mechanical room open and opened all ceiling vents to let some cool air circulate in the basement. Only place I have sweating still is at the unit itself up by the supply plenum box and the round portion duct above it that disappeares up through the mechanical room ceiling which then goes all the way up past the 2nd story and into the attic distribution box which then supplies cool air to the rooms up there on second story. I did find some cool air LEAKING out from around the collar where the plenum box connects to the box above it! I'm confused...

 

[Fireguy5674]

I am not sure what is confusing you. Any place you have the possibility of hot, humid air coming in contact with cool metal you will have condensation. I'm sure you know that. Now the question is where is the hot humid air getting into the area where the condensation is occurring? Also, if you let the unit run another day or two will the area where you are seeing condensation now finally get cooled down and the problem will correct itself? Can you direct a fan into the area and get it cooled down? Is there hot air leakage from the attic? Many questions I cannot answer from my computer chair, sorry. Go back and do a careful inspection of the area and see if you can come up with something you did not see before. Is there staining that would indicate this is an ongoing problem that was never addressed properly?

If you are concerned that the air leak you were talking about is contributing to the problem, you can buy foil tape that is for sealing ductwork and seal the area. They also sell ductwork caulk which will seal your leak. Depends on the exact problem and location.

 

[Billbill84]

I am not sure what is confusing you. Any place you have the possibility of hot, humid air coming in contact with cool metal you will have condensation. I'm sure you know that. Now the question is where is the hot humid air getting into the area where the condensation is occurring? Also, if you let the unit run another day or two will the area where you are seeing condensation now finally get cooled down and the problem will correct itself? Can you direct a fan into the area and get it cooled down? Is there hot air leakage from the attic? Many questions I cannot answer from my computer chair, sorry. Go back and do a careful inspection of the area and see if you can come up with something you did not see before. Is there staining that would indicate this is an ongoing problem that was never addressed properly?

If you are concerned that the air leak you were talking about is contributing to the problem, you can buy foil tape that is for sealing ductwork and seal the area. They also sell ductwork caulk which will seal your leak. Depends on the exact problem and location.

Well it's just confusing because I have two issues going on here. One is the condensation issue previously mentioned that was relieved, on supply ductwork that was with 10ft after it left the furnace/AC unit as shown in photos. All I did was open doors to room and open all ceiling vents in that basement. Only area I'm seeing some sweating is on the unit itself still right above the plenum in the supply direction that does into my very hot 2nd floor. I'm wondering if there's a back draft of some sort because the return ducts in second floor are pulling hot air cuz it's so damn hot up there(cape cod style home). Second floor rooms are like box structures IN the attic. In winter, it's cold as heck up there so obviously there an insulting issue. I'm wondering if this may have something to do with my unit sweating? Should note that drainage to condensation pump seems to be working properly...

 

[slownsteady]

....you could always insulate the duct.

 

[Billbill84]

Hey guys! Another update. Sorry kinda long but I need some clearification here. So get this, this whole thing breaks down into 3 issues. Hot second story, sweating ducts, sweating unit.
It all started because the second story in my Cape home the 3 rooms + full bath were hot as hell up there, main level cool 73 and basement obviously about 68. So investigating I went to basement made sure no dampers were closed. And found sweating ducts and sweating on the unit itself. Fixed duct sweating by opening all vents in basement. But sweating still persists on 2 areas on the actual unit. See pics! It's on the supply side only in 2 "boxes" just above the unit(not sure what they're called or what's in there). It's like it skips sections where it's sweating kinda weird. So that's the second issue. While investigating the hot second story, I got up in that attic to check ducts out. Everything looked normal BUT after looking at the supply lines I checked the returns and found 2 of the bedrooms had the return pulled up and out of the duct portion that goes down into the wall return vent!!! They were just laying over the holes, ripped out!! This tells me the returns were just sucking hot attic air into the system! Looking closer I see each had a damn black cable wire going down into the hole feeding a wall jack down in the room (remember I'm on top of the rooms ceiling in the attic). I went down disconnected from wall and pulled them out and reseated them properly screwed them down right. So question is, could this have something to do with all these issues with upstairs being hot and the AC/furnace unit sweating up high were it leaves the basement to feed them supplies to the second story? So far the house seems to be cooling a little better but that sweating on the unit is there in the spots I circled in the pics.