Insulating a Whole-House Fan

Dear NH,
I have a belt-driven whole house exhaust and that is mounted above the ceiling in our hallway. I want to install some sort of insulation to keep the cold air from coming into the house. I can't install the type of kit that covers the fan from above because I would have to walk about 80 feet through 3' of insulation! Currently, I use plastic storm window "stretch wrap", but it doesn't provide much insulating value. The fan is made of a non-metallic substance so magnets will not adhere. Does anyone make a kit that attaches to the surface of the louvers?

I wouldn't depend of magnets holding anything overhead. Gravity is unrelenting! I am unaware of any prefabricated kit you could purchase for this application. Using the plastic storm window was a creative solution and probably helps more than you think; of course, adding some sort of insulation would give you even more energy savings. Though it would take a little effort twice a year, you could take down the louvers seasonally and replace them with a smooth plywood board (1/4"). This board can be painted or stained, and can even be "dressed up" with mouldings, depending on your desire, abilities and creativity.

Match the locations of the mounting holes to the louvers and if you want, use the same screws to install it. Once you have access to the area above the louvers, you can decide which type of insulation will be the best for your situation. A solid board insulation such as Styrofoam, cut to fit as precisely as possible, will give the most insulating value per inch of thickness and also be neat (especially as opposed to fiberglass). You could also put some fiberglass into a plastic bag or two and push that into the opening to provide insulation. Yes... I know that gravity is your enemy, so you will have to be creative in finding a way to make the insulation stay in place. Whether you can attach it to the wood cover will depend on the framing beneath the fan.

Some attic fan installations leave the ceiling joists in place. If so, your opening will probably have a ceiling joist crossing it, which will allow you to press bagged insulation into the gaps on either side of the interloping joist. This will provide an adequate air seal and provide neat, reusable and efficient insulation! Of course, even if you didn't use any insulation at all, just having a solid cover as opposed to the louvers (or the plastic film) will make a dramatic difference itself.

To make take-down and installation easier, you can replace the original screws with double-threaded screws. These screws have wood-screw threads on one end and machine-screw threads on the other. Once installed, you leave the screws in place and just remove washers/nuts to change covers. To initially tighten this type of screw, put a nut onto the machine screw end all the way on and use a wrench to turn the screw. The nut may be a little difficult to remove, but you can hold the machine threads with a pliers to keep the screw from turning while removing the nut. It is better to grab the machine threads near the middle, not at the end. You might damage the threads enough to make it difficult to start the nut next time! Any slight distortion in the "middle" threads, though, will be adequately straightened when you remove the nut.

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