The first photo below shows the blower I installed on the ceiling of the first-floor “garage” section of my barn. I did that well over a year ago, and it's just been sitting ever since. That's a very conventional squirrel-cage blower, running on a fractional horsepower synchronous motor (so very efficient), blowing straight up. Above that exhaust port on the blower is a rectangular duct I built out of wood, leading through the ceiling (which has 8" of insulation in it). The second photo shows what's directly above that blower, on the second floor of my barn. This is out in the storage section of the barn, which is uninsulated and unfinished. You can see the top of the wooden duct I built, and the beginnings of the plenum box. That box is made of 1/2 OSB skin with 2x3 stringers, and stuffed with insulation. One the inside you can see the “rails” I fabricated to hold a standard 16x25x1 filter (and you can see that filter installed on the last photo). The next thing I built was the top of the box, a slightly complex assembly (fabrication in progress on the third photo). Finally, in the last photo you can see the almost-complete plenum box – only the front door remains to be built, and that will be my first job this morning. Once that's complete, the downstairs blower will pressurize this plenum box, and filtered air will exhaust through the 6" duct connection on the top. The next step after that will be to install a “boot” in my office and connect it to the plenum box with flexible insulated ducting.
