Working out the dimensions for the HRV baffle box. I'm thinking 18" wide (out to out) so I can fit mounting brackets on the 16" OC studs. Using 6" tall baffle chambers (big enough to clear the 5" ID round ducts) to create 1 full and 2 half turns per side (intake and exhaust), I'll end up with an overall box dimension of 36.4" tall x 18" wide x 6" deep.
The build will be doubled-up 1/4" plywood with Green Glue in between each layer, and Green Glue sealant along all of the adjoining seams. I'll skin the outside of it with T/G cedar and then corners to match the building's. The intake and exhaust vent holes, which can be as large as 4" x 12" will be standard exterior vents in a black finish. The exhaust vent will be placed on the underside/bottom, the intake on the top of the front face. This will keep the conditioned and unconditioned air from mixing, which would defeat the purpose of the HRV (admittedly the factory arrangement without a baffle box doesn't do a good job of keeping this from happening, so this will be an improvement). Lastly, a wide drip flashing on the top to keep the rain away from the vents will finish it off.
I'll also be building a much more simple box with the same doubled-up plywood, Green Glue and cedar where the mini split punches through the wall. A mini split is a closed system (i.e. it's more like plumbing than HVAC), so I can't put baffles in it, but the box and Green Glue will help with isolation along the north wall all the same.
The weather is about to get gross here in Seattle, so it might be a week or two before I get to it. Hoping to knock out some vestibule tasks this weekend. Keeping my fingers crossed that my motivation holds out and I actually do it rather than just going into the main room and working on this jazz composition I've been at for the last week
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