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: 
There are covers you can purchase, or easily make, to insulate your attic fan. The cover attaches to the bottom of the fan (inside your house) with magnets or velcro. The magnets are cosmetically more appealing, as you'll see the velcro when the insulation is not on. It's very convenient, because you don't have to climb up into your attic to remove it every time you want to use your fan.

Purchase a soft sheet of insulation material and magnetic striping. Cut the insulation material to match the size of your fan, then attach magnetic striping to the outside edges of your material. When you want the fan insulated, stick it up. When you don't, just pull it down. 

An online search will find you many options.
You could make an insulated panel that is spring-loaded to the open position. Keep it closed with door holder magnets [like this](http://www.americanlocksets.com/lcn-sem7850-magnetic-holder-p-4178.html) .You could wire the fan and magnets to a double pole switch that cuts magnet power at the same time it turns on power to the fan. Might cost a bit and take some research... but it would be cool (pun intended)!