Sealing/Insulating exposed ducts for evaporative cooler in Tucson AZ
I’m just getting done helping relatives move into a house outside Tucson, AZ. The house has an evaporative cooler on the roof ducted to each room. The ducts run out of the side of the evap cooler and across the roof splitting a few times and then heading down through the roof into each room. The ducts are rectangular metal ducts, sealed with mastic and then lightly painted brown.
Given that it’s 110° outside during the day and the sun beats down directly on the ducts, my thinking is that this is like AC ducts in a hot attic, but worse 🙂 A quick inspection shows that the ducts feel cool to the touch close to the cooler but warm to the touch at the far end. Basically the swamp cooler is working really hard to cool the ducts, instead of the house!
In a perfect world, I don’t see why any ducts would run outside and, worse, be in direct sunlight. The medium term plan might involve ductless mini-splits, but the evap coolers have great advantages in the desert, including helping raise humidity in the house (3% relative humidity here today) and allowing/requiring doors and windows to be open, which is a welcome change from a sealed up AC house.
But in the short term I think there are two tasks: 1. Air-sealing the ducts 2. Insulating the ducts.
They aren’t too badly air-sealed, but there are a few leaks here and there. From quick inspection the mastic looks to have dried out and cracked in a few places. Does anyone have advice for sealing ducting in brutal sunlight? Considering metal backed tape; presumably any seam that is getting sealed with tape would have to have the paint and mastic stripped off before putting the tape on?
The insulation plan is to wrap the ducting with 2 layers of 1 inch polyiso overlapped and woven at the corners, sealed with metal backed tape. Any thoughts on which tape, given the brutal sun?
A more radical approach would be to remove the ducting and drive the air only into one room, but there are concerns that that would mean that one room would be freezing (the evap coolers can really drive cool air in the desert overnight).
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