Yes, it can be done. My boyfriend built our coop and added the exhaust about a year later.Is there a way to put in an exhaust fan with something that is already built?
I asked him to give me a quick primer on how he did it: He had to open up our "ceiling" in the coop, add an exhaust vent in the ceiling, and add the ducting, the fan, and an exterior register with flaps so birds and such wouldn't get in when the fan isn't running. He said ours is a high-volume hydroponic fan (for exhausting grow rooms or something like that). The ducting is flexible running from the ceiling exhaust register 90 degrees to the fan intake, then out the fan to the exterior register. He said he could have just mounted a fan in the ceiling and exhausted the heat straight into the "attic" but that he didn't want to force that much hot air (800cfm) into that small space since the soffit and roof vents weren't designed to transfer that much air volume.
He pulled power from an existing switch or outlet in the coop, ran the wire through a thermostat placed at the height of the birds, then pulled the wire to the fan and connected it. The fan has power all the time, but only comes on if the thermostat is adjusted to meet the current or higher temperature in the coop. To turn it "off", we turn it down to below the current temperature. We also use two oscillating fans on timers that run from about an hour before the birds go up until midnight to cool the coop as much as possible until the outside temperature does that naturally.
It's worth noting that we don't have open rafters or trusses in the ceiling if that helps to visualize it; the ceiling is covered in 1/4" plywood, and there is a 14" x 14" return air fixture (like you'd use in a home) close to the center of the ceiling between two of the ceiling joists.
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