Ductwork in Exterior Wall
I know, don’t do it. Here is my problem. I am renovating my daughter’s house. She wanted a bearing wall removed and I knew that two supply ducts would be an issue. They are 6″ ducts running from the basement to two second floor bedrooms. Furnace is near the center (front to rear) of the basement at the end of the basement. Bedrooms are above this end of the house.
The 6″ round come off the main plenum and within a couple feet convert to 6″ oval (which I think gives airflow more like 5: round). This goes up the center 2×4 wall and then turns and runs 12′ to the front and to the rear of the house where is meets baseboard type vents. The velocity at the vents seems fine, but the daughter just bought the house and has not lived in it yet, so I don’t know how heat or AC is.
I proposed enclosing 6″ round ducts in the front and rear corners, but she did not like that option. Because of floor framing clearance at the foundation and other issues this would also require use of a number of elbows and significant framing changes. Besides the work involved, I think the elbows, etc, would more than offset any improvement gained by using 6″ round ducts.
My present thought is to use wall stack duct, The exterior walls have Polyiso wall sheathing (I’m guessing at least 1/2″, but the wall seems a bit thick, so maybe it is more. I am thinking about using 2-14″ wall stack so that I do not have to hack into the band joists and so that I can place about 1″ of foam insulation behind it. I will also foam at cavity joints and adjacent to the ductwork. I have not found much information in 2-1/4″ wall stack ducts, but I’m thinking that 12″ to 14″ wide ductwork will probably give me at least equal and probably better airflow than the oval ductwork. I would also be eliminating 1 oval elbow. At the second floor I need to jog the duct over 3-1/2″ to meet the vent. This is about a 15 degree angle and then the duct terminates directly at the vent so essentially I eliminate another elbow.
Sorry for the long post. Any thoughts on airflow or efficiency in the exterior wall?
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