Wow two replies and two direct bullseyes!!! Thanks folks, I had surfed 'til I nearly drowned on this subject and couldn't find a thing--I was THAT CLOSE to suffering the extreme humiliation of having to call the mfr about this! ;) >Apparently the motor is a powerful magnet motor because if it was a brush type it would burn up. Dunno what a "magnet motor" is gardenerwantabe but like you I tried to hold it with my hand and it clearly was Not about to yield to me! >I found that the bar is DESIGNED to stop the motor arm Good story gardnergal; something that confused me was in the motor instructions where it says "don't let the armature be stopped by the motor housing" which implied to me that it would grind itself up. Apparently that warning is just to assure the shutter opens fully!!? Thanks again; you-all have reassured Me and no doubt future generations of hobby GH builders (who use google)! Maybe when I get a rainy day I will email the mfr and suggest a Sequence of Operation paragraph for their "installation instructions"!

I would. A gravity shutter can blow open on a cold windy day which will allow cold nasty air to enter your warm greenhouse.

I'll explain why fans and shutters are typically mounted with the flange on the inside of the openings. You'll notice that the weight of the unit (and especially fan units) are not evenly distributed and the guts enclosed in the box are usually hanging on the outside of the opening. If you mount them with the flange on the outside, it puts all the stress on the mounting screws, instead of distributing around the whole unit by way of the flange. The weight of the units also push against the opening and cause there to be a tighter fit simply from gravity. And believe it or not I've seen screws fail and loosen simply from fan vibrations over the years. If the flange is on the inside, and the bulk of the unit on the outside, the unit is more stable, and the bottom edge of it is then weight bearing, taking the stress off the screws. It's probably obvious I work with pretty large fans, and motorised shutters, but the principle of it is valid regardless of the size units you work with.

I found something online called Shuttereaze that looks like it would be great for my plantation shutters, but it isn't for sale yet and they don't list prices. If this actually ever becomes a real product that works as described and isn't overpriced, I would likely get it. Youtube video link below. Here is a link that might be useful: https://www.youtube.com/watch?v=BKJSqjFHWQ8