"even out the temps throughout the home." I'm more interested in cooling the loft, evening out temps is added benefit. Design of tube to fit decor. A rectangular tube would be easier to attach registers to, larger size fans of equivalent relativly low CFM easier to find than smaller. But many ways to do this. What ever floats your balloon, I always say, well, not always but sometimes. Actually i don't think I ever said that B4.
Wuzzy, the spring should be attached to arm or lever, outside actual chute, attached to damper, so as not to snag clothes. Series of holes in lever or bracket to adjust tension.
GB, don't nobody care what OP did, if anything. We're developing the Laundry Loft Cooling Fire Introducing Emergency Exit Tube, or LaLoCoFIEET, as it is known in the industry, here. Just in case we ever run into similar problems. Also, OP mite spend Big Bucks, Installing and blocking vents, insulation, knocking holes in walls, suing and being sued by Condo ***., then return and see how cheap and simple LaLoCoFIEET is. ( Deluxe model more expensive, the DelLaLoCoFIEET) We all laff. Never rush into things, I always say, well not al...I awready been there.