A/C ductwork condensation problems with only certain vents

11 years ago

Hello all, I added an A/C air handler and ductwork in my attic when I added on to our house about 5 years ago. I have a hydronic heating system and a lower ceiling in our basement that wouldnÃ¢ÂÂt work well for adding ductwork. I am trying to figure out why only certain ducts in my attic are getting condensation in them. I live in MN and the winters are cold so every fall, since I installed the A/C system I have had issues with condensation so as each year passed I have taken measures to prevent this from happening. I have plastic bags of insulation I stuff up each vent which is at least a foot or more of insulation, all my ductwork is rigid and has R-10 insulation covering it. I also have round discs I cut from Reflectix material to place into the opening and then push the round vent hood up into place. I also have insulation I put into garbage bags, so they were more flat, and put those up into my 3 returns, then used the window plastic shrink wrap on the outside of the returns to seal them shut. I have even gone to the trouble of plugging up the drain tubing coming out of the house to prevent any other moisture from entering this system. I finally thought I had taken care of this issue this last year but for some reason 2 supply vents and 1 possibly 2 returns had signs of condensation either on the bags of insulation or the bathroom which I can see the water clinging where the 90 degree elbow turns downward. The 2 supply vents and 1 of those returns are in my master bedroom suite which of course is the addition but all of the ductwork was added at the same time. So what is going on? Do I need to put that window sealing plastic on the outside of all my round plastic supply vents? I realize now that it was a bad idea to add this in my attic but are there any other ideas out there that I am not thinking of to prevent condensation from forming? The older part of the house had leaking vents also until I added the insulation bags, since then those havenÃ¢ÂÂt had any moisture problems.

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Comments (8)

fsq4cw
11 years ago
This is just a thought and IÃ¢ÂÂm guessing here but how well is your attic ventilated? Do you have soffits that breathe and adequate roof vents that remain above any snow accumulation in the winter? The attic should be at the same temperature as outdoors to not accumulate moisture.

SR
dave120
Original Author
11 years ago
Thank you for commenting on this but how does the moisture from the attic transfer inside of the ductwork when it is tightly sealed up with mastic, aluminum tape and the thick blankets of insulation? I do have ridge venting and make every attempt to get the snow off when it comes. The addition which has the most problems is vented very well with each soffit vented. The older attic area that doesn't have any condensation issues needs imrovements for better soffit venting. I improved it somewhat when I had the siding and soffits replaced using a sledgehammer to remove the blocking just so I could HAVE vents because someone must have thought that it might get cold up there if it open to the outside.(sarcasm)
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dave120
Original Author
11 years ago
Now that I have had time to think about it a while. The only way condensation can form inside the ductwork is when there is humidity entering that particular duct, correct? Would a likely suspect then be if there is any type of air leaking even a tiny amount into those ducts that have a 3 foot or so lift into the attic before they turn horizontal to go into the trunk line?
Justa thought but I have other vents in other parts of the house that way and they do have not ever had condensation even after the 1st winter when I didn't know I had to seal them up.
fsq4cw
11 years ago
I donÃ¢ÂÂt have all the answers, maybe I donÃ¢ÂÂt have any. I was just trying to provoke some useful analysis of the problem. The attic and everything up there should be as cold as possible.

You mentioned that the new addition has most of the problems and the older attic has none. Might this be because the newer section is too tight and the older one Ã¢ÂÂbreathesÃ¢ÂÂ?

You should not have to clear snow off the roof with proper roof vents. See link below for roof vents designed for a cold climate. TheyÃ¢ÂÂre very common here where snow can be quite deep on the roof, I donÃ¢ÂÂt know if theyÃ¢ÂÂre common in your region. They always extend above the snow.

SR

Here is a link that might be useful: 'Maxie Vent'
User
10 years ago
Only R10 above the ducts? That's a BIG problem. If you have ductwork in the attic it should be below the insulation level, which should be R-40 something in your climate. You shouldn't be stuffing anything in to the ducts at all. You should have proper vapor barrier at the ceiling level, then the R-40 over that and the ducting, and then the attic itself should be properly vented. You'll never seal the ducts well enough to account for air infiltration, and you will always get condensation when the interior moist air encounters a poorly insulated space above.
dave120
Original Author
10 years ago
I should clarify that I have at least R-40 insulation levels in my attic if not more. I have R-10 insulation wrap for my duct work only. I have vapor barrier on all the ceilings. I find it very odd that some ducts I have in the older part of my attic are running above the insulation but do not have the problem like the ones in my addition that run above the insulation level. I was thinking that I should rerun the duct work for the 2 that are creating such an issue. Thanks for the reinforcement. I will look at getting some pictures of these ducts and ones that are run the same way but not posing any issues.
Servicetech
10 years ago
How cold is the air coming from the registers? You may have low airflow causing your ductwork to be too cold.
dave120
Original Author
10 years ago
I need to use insulation bags to seal the ducts during the winter since they are only used for A/C so I do not what the air temp is. If you are asking the question for when the A/C is running in the summer, the temp is the same coming out of all the registers and the airflow is very good.

A/C ductwork condensation problems with only certain vents

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A/C ductwork condensation problems with only certain vents

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