2" Vent lines within 2x4 walls would be very tricky, and I think the holes would exceed that allowed for even non-loadbearing walls (2.1" is 60% of 3.5"). I was thinking about this same setup in my basement bath.
For me, I could use 1.5" vents, but for a whole house, I don't think that is adequate.
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Scott Sabin
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