It's a Maxxair heavy duty exhaust fan with integrated shutter - 14" fan diameter. Rough opening is 20.5" X 20.5". Hubby says it's way too big, but "Ask your friends on that chicken website." Here's the link to the Tractor Supply fan: http://tinyurl.com/23m6whm Here's my coop under construction. I was thinking to mount it in that upper right corner facing the camera. Oh, and only half of this building is my chicken coop. Hubby gets the other half as his workshop.