hum. Interesting ... Our neighbor came over today and watched my husband working on installing an electric fan in the ceiling vent in the GH. They have the same HF GH 6 x 8 as we do. He wondered why we wanted a fan in there and suggested we just open the ceiling vents. They don't actually grow stuff in their GH, I guess, because here in Central Texas we had some days this winter when my GH temp was 85 degrees and rising and I had two floor fans going and vents open. They don't have any electricity to their GH either. Anyway we got a chuckle out of his puzzlement.
I will post pics of the fan when done. It's a "fantastic fan" we saved when we had a fancier model put in our 5th wheel camper a few years ago and my hubby was sure it would come in handy for something...it is! He is waiting on one little part and it will be done.