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Community and Q&A

Preventing Condensation on AC Mixing Box

SFulton | Posted in General Questions on

We have a two-story home in southwest Florida, and within our floor trusses between the first and second floor we have an AC mixing box above our kitchen that keeps sweating due to the fact that it is in a system that is open to soffits around part of the first floor. We do like to keep our interior fairly cool in the summer, and with our crazy humidity the sweating on the mixing box, actually started to drip onto our kitchen ceiling and made a wet spot. Our AC company came out, opened up the ceiling in our kitchen to access the mixing box and completely replaced it and insulated it well, but it obviously is still sweating because we are now seeing wet marks right underneath where it’s located on our ceiling. Is there a way to prevent this from happening? Can we create a closed system and install an exhaust fan or something? We need to have most of our soffits replaced due to extensive damage from Hurricane Ian that we recently had in September, so now would be a great time to redo the existing setup. Thanks in advance for any ideas/suggestions!

Samantha Fulton

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  1. walta100 | | #1

    It seems almost every builder in the south thinks the attic is the perfect place to locate the HVAC equipment and duct work I think it is stupid and it is impossible to change Bubba’s mind.

    The question is how long will you own the house 6 years is average.

    If you’re going to sell in the next 15 years have a drip pan with a drain installed.

    If you going to stay a long time you could move the insulation to the roof line and condition the attic you will use slightly less energy and the ducts will not sweat.

    The best plan is to get the HVAC out of the attic, think ductless mini split heads might make sense if a dead system is being replaced.


    1. SFulton | | #2

      Unfortunately where the problem is not the attic, but the roughly 16” floor trusses in between the first and second floor, hence the difficulty in solving this problem. Our HVAC systems are located in our house, but we have a mixing box where separate ducts come off of to feed separate vents. The actual mixing box is what is sweating. We have already lived in this house for 16 years and plan to be here at least another 10+ (forever according to my husband) as we built our dream home.

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