Question: I have a whole house fan installed in my house from the previous owners. I love the fan, as it lets me cool down the house quickly in the evening -- or after I fill the house with smoke from forgetting about food on the stove! :)

However, as I try to air seal my house it is immediately apparent that the whole house fan is by far the leakiest thing in the house. Under a blower door test, the fan louvers actually open up and most blower doors can't achieve the pressure they normally operate at in order to perform a measurement.

I would like to install some sort of air tight louver or door on top of the fan in the attic that will close tightly until the fan switch is turned on, at which point the louver or door will open. The closest idea I've had for that so far has been a plywood door that closes over the fan against weather stripping and is opened and closed by a linear actuator, and then attaching insulation to the top of the door, but it really seems like overkill to build and maintain a system that complex.

I'm also aware of one commercial air sealed and insulated whole house fan, but it is $1,500 and pushes 2500 CFM *less* than my current fan. $1,500 buys a whole bunch of plywood and linear actuators if I do end up having to go that route.

I've also looked at motorized dampers, such as [this one](http://www.grainger.com/product/DAYTON-Damper-3C729?s_pp=false) from Grainger, but due to the small width of each blade I wouldn't be able to put any reasonable amount of insulation on them. Also, they're rated for 3500 CFM for some reason, and the fan I have easily does at least 5500 CFM.

Does anyone have any better ideas and suggestions for how to accomplish this? Note that I am **not** interested in solutions that involve manually removing a lid, seal, or cover from the fan; this needs to be automatic.

Answer: 
Check around the farm supply places - they carry big dampers. I used to have one about 36" square (the ex still has it). Try places like [here](http://www.farmtek.com/farm/supplies/home) and [here](http://www.tractorsupply.com/).
Brainstorming here, but a heavy enough door with a rubber gasket, that can rest on a gasket on the fan might do the trick. the levers to lift the door away will have to be strong enough. The only other idea is a set of electromagnets that could "pull" the door shut...wish I could offer a better solution.