Five Percent: Conserve Energy

Climate Change Is Important: Energy Conservation is the First Step

September 21, 2009

Insulate Your Whole House Fan for $20

Category: Energy Audit,Household,Save Fuel,Tips – Tom Harrison – 10:13 am

In the summer, we use our whole house fan to stay cool — it draws cool, fresh evening air through the house making us comfortable enough that we never used an air conditioner this past summer. Our electricity bill was great.

But now that it’s fall, we might as well call it a “house hole” instead :-)

We have a 32″ square hole in our attic. We had an old mattress cover that was about the right size and we tossed it over the top every fall thinking, “close enough”. Then we had our energy audit last Spring, and this is what we found: the picture on the left is of the louvers that cover the fan opening when it’s not on; the picture on the right is an infrared photo of the same area taken (with our mattress cover installed). Blue is cold, and cold is bad.

House Hole (click for full size image)

Whole House Fan, or House Hole (click for full size image)

You can also see some un-insulated areas along the top of the window, as well as around the fan itself. But that dark blue area is right in the middle.

Blue is bad.

Since the energy audit, we have had the house insulation filled in where the first contractor messed up, and topped off the insulation in the attic. But I still needed to improve on the mattress cover.

How To Make A Whole House Fan Cover



One word: rigid Styrofoam insulating panels.

You can get them at an lumber yard, or home store like Home Depot or Lowes — I bought 3 pink panels, 2 feet (24″) wide, 8 feet long and 1 inch thick. But first I measured.

Oh, and a roll of duct tape, wide if you can find it. Total cost for three panels and tape was about $20.

The trick is to make a box with one face open. This isn’t precision engineering, so give yourself and extra inch. My fan opening is around 32 inches square, and about 14 inches off the floor to clear the motor. These are the inside dimensions — you’ll need to add an inch to the length of the sides to account for the thickness of the panels. Start with the 4 side panels.

You can mark the measurements on the board — I used a pen and a 4″ carpenter’s level. If you don’t have the level, any straight-edge will do.

There are a couple of ways to cut this insulation. If you have a sharp blade on what used to be called a “Stanley knife” (before 9/11, now “box-cutter”) you can make a nice clean cut — just pull the blade smoothly. With 1″ board, the blade will cut almost all the way through — I just snapped off the remaining part. If you have thicker board you can cut in from both sides and snap it. If you have power tools, you could also use a jigsaw or sabre-saw if you wanted, or for that matter a circular saw. A carpenter’s finish saw would work, too. In a related job, I used a hacksaw blade mounted in a frame designed for cutting in tight places, which lets the blade extend out. I would not recommend a chainsaw. Bottom line: this doesn’t need to be finish carpentry.

Cut the long way first for the box sides, then out of the two long pieces, cut four sides to length, in my case, 33″ x 14″. Overlap one edge with the other and tape the first two sides together. Try to align the tongue-and-groove edge the same way, and make sure what will be the top edge of the box is about the same height so the top will fit on flat. Keep working around until you have all four sides taped together.

Now for the top. Lay down an un-cut board over the box edges, and tape two of the sides temporarily — aligning the two edges of the board with the box sides will make everything nice and square. Use the underside of the opposite edge to mark the length of the board and cut it (you can take it off the box sides). The other half of the remaining board should fit, tongue-and-groove and make a nice seal — mark the undersides, and cut them.



Now just assemble the remaining pieces with duct tape, and voila — a box.

I am still experimenting with methods for creating a good seal between the box and the attic floor. I bought a can of spray foam, which might do the job. Or maybe just duct tape — my attic floor is just rough-cut boards, so that poses a little challenge. I am thinking of creating a permanent flat surface with left-over rigid panel that sits on the floor and seals tightly against the fan frame — this might be a good idea in my case — if your attic has a nice plywood floor then you’re probably all set.

In any case, this is an air sealing job with an insulation component. The duct tape will do a good job with air-sealing the box itself. The insulation value of the 1″ rigid board isn’t all that great — R 2.5, I think, but I think this will be a far better outcome than the old mattress cover.

This job took me about a half hour once I had the board home from the lumber yard.

How To Do It Right the First Time

tamrack-self-insulating-whole-house-fanAll of this insulating was needed because I bought the cheapest possible fan from Home Depot. It’s loud, was difficult to install, and despite the gaping maw I hacked in my ceiling, does only a pretty good job of sucking air through the house.

If I had it to do again, I would get a top quality, quiet, self-insulating whole house fan that didn’t require cutting a ceiling joist, since it is narrow and designed to fit a standard 16″ width between joists. This model has two smaller, quieter fans; when on, the doors open up to let air flow; when off, then close down and have a thick layer of insulation on top, built right in.

Oh well, live and learn.

Our energy audit found two other gaping holes in our house, and the rigid pink Styrofoam panels are a good solution for those, as well.

More adventures in air sealing to come :-)


  1. The most efficient heating and cooling systems are useless without proper insulation.

    Comment by Charles — September 26, 2009 @ 7:34 pm

  2. Lowes carries the Shuttercover Trim to Fit which is insulated and goes on the ceiling side of the louvers with self adhesive hook and loop so you don’t have to go into the attic. Easy to install and remove.

    Comment by Rick — November 11, 2009 @ 1:06 pm

  3. The above comment is actually right. Whilst blocking air vents, and draft spots does slow the rate of increase or decrease in temperature the most effective form is to actually insulate the ceiling or walls themself.

    At perth insulation we reccomend insulating the ceiling first. If you are living in Australia or the US the governement offers rebates and financial incentives to insulate your home to reduce your energy consumption. This is a great reason to get insulate your home today.

    Comment by Perth Insulation — February 2, 2010 @ 9:21 am

  4. Just wondering what kind, if any, changes you saw after putting this over your whole house fan when it comes to your electric bill and/or the feel of the home in that area?

    Comment by Debbie — March 22, 2010 @ 12:07 pm

  5. Debbie —

    We did a lot of things last summer and fall, one of which was insulating the whole house fan. The house has been dramatically more comfortable (fewer drafts, cold spots, etc.) and we have used significantly less heat than in past winters (it’s looking like about 30% to 45%) – not just from the whole house fan cover, but all the changes we did combined.


    Comment by Tom Harrison — March 22, 2010 @ 12:24 pm

  6. I am slowly working to cut energy costs in my home.

    I have installed windows and doors. I am taking bids on efficient heating and a/c to get all possible rebates. Insulation is next.

    I find that I cannot tolerate a/c. I feel confined with the windows shut. I resent the cost of the a/c.

    I am personally heat tolerant but very intolerant to cold.

    I want a whole house fan but I am sure it will breech the insulation in the attic.

    I use many fans in the house, including cheap box fans in two windows.

    Apparently, whole house and window fans are not popular enough for technological improvements to be provided.

    I spoke with the whole house fan installer about constructing a proper cover for the fan, like the one shown here, only maybe with heavier insulating materials.

    He looked at me in a dazed way.

    Who would not pay a little more for a proper; i.e. tested, cover and a slight service charge for one of their workers to take it off in spring and put it on in fall. Insulated batting could even be laid over it in fall.

    They should even be able to build one that can be raised and lowered with a simple mechanism in the attic.

    I have given up and am looking at a high velocity window whole house fan. They are available only on line, and I have no experience or information on the sellers.

    The whole house fan is a good idea that needs modernizing.

    Please tell me if you have solved this problem. I want to avoid a/c as much as possible.

    Comment by Lisa — June 2, 2010 @ 6:36 pm

  7. Lisa —

    I am with you on the whole A/C thing. It’s pretty much bad in every way (which is perhaps easier for me to say than someone who lives in Georgia…).

    Yes, my whole house fan cover worked very well. I had a follow-up audit and blower door test which did find that my first attempt was only a modest improvement — I had failed to seal the boundaries of where the fan louvers penetrated the ceiling, so there was still significant air leakage. It took two cans of foam to completely seal underneath the fan (making my total cost more like $40), but in the end, it was a successful project.

    The key lesson I learned in all of this is that you may as well forget insulation until you have proper air sealing (with foam or caulk, or duct tape).

    Two other things to consider: first, the link I had in original piece to the Tamarack fan above was broken, and should now be working properly. Reports are that this is a better device in many different ways than a traditional whole-house fan. Second, consider ceiling fans. We have several and are thrilled with them. Since I originally wrote this post, I now work for Energy Circle, and wrote a piece on a whole house fan I recently bought and completely love, so check it out.

    Comment by Tom Harrison — June 3, 2010 @ 9:51 am

  8. I trie one of those self insulating, no cut fans from home depot. Complete waste of $400. It was extremely loud (small fans must run at higher rpm to get the cfm) and didn’t move near as much air, not nearly enough to cool my 1500 sq ft house (and I live where it drops to 60 at night and is dry, perfect whole house fan weather).

    I ended up donating the fan to my local Habitat store and buying a normal 36″ fan. It moves 6000cfm, more than 4 times the other one, cost half as much, and is much quiter.

    Comment by Matt Warshawsky — January 9, 2012 @ 11:11 am

  9. Hey Matt —

    Thanks for your comment. Do you remember the brand name of the fan you purchased? I used to work at and we sold a self-insulating fan that was supposed to be very good, very quiet, and very efficient.

    The fans we sold also had the distinct advantage of being narrow enough to fit between ceiling joists thus avoiding the rather significant effort of cutting a big hole in your hallway ceiling, framing it, etc.

    It wouldn’t surprise me if the Home Depot knock off sucked :-)

    Comment by Tom Harrison — January 9, 2012 @ 1:26 pm

  10. Alas, I don’t. It was several years ago. I bought it because it fit between the joists and had the automatic closing insulating panel, despite the fact it cost close to $500. It also had a remote control which meant I didn’t have to wire a switch into the wall. And it said it was whisper quiet.

    As I said, it was horribly loud and didn’t move enough air. I don’t really see how a fan with short blades could possibly be as quiet as a 36″ fan, since to move the same air, it has to run a lot faster, even with two of them in a unit. And for that matter, it didn’t move the same air. The 36″ I replaced it with cost $250 and moves some serious air, cooling the house to 60F at night and making it so I don’t have to run the A/C at all.

    Perhaps there are better ones, but I wanted to put it out there that they are not all good. Just because something says its quiet, don’t believe it until you hear for yourself, and certainly check before you plop down $500. If you want to try one, make sure and test it before you install it, and make sure you can return it.

    Comment by Matt Warshawsky — January 9, 2012 @ 1:53 pm

  11. I would not cover just the top of your attic fan as in the article & pics above. I covered my fan with a 9×12 plastic drop cloth and then layed rolled insullation over that. When I uncovered the fan in the spring I saw that the fan motor and capacitor has rust all over them! Heat & moisture came up through the fan grate and was then trapped by the plastic/insullation. I then built something like above contraption using the 2″ thick styrofoam board insullation. I used calk and large 3″ screws to hold it together. I don’t put it on tight to let the moisture vent a little, but hope that it slows the heat loss from my house. I just came across this
    I’m going to order the Seal-A-Vent(cut to fit) insullation cover. This should help to keep the moisture in my house and not let it go up throgh the fan grate. Then I’m going to add 1″ wide soft foam insullation tape to 2×4’s framing the fan and then when I place the box I made similar to the one above it should seal up pretty nicely.

    Comment by Tony — January 20, 2012 @ 3:40 pm

  12. Matt/Tom….I’ve been doing an exhaustive search on whole house fans and I’m finally opting for a belt driven 30 incher by Air Vent. There is a killer deal on one at my local Lowe’s for $89 clearance. I can’t pass this up at a regular price of ~$300. In any case, what I’ve found out about the ‘boxed’ units like the ducted Quiet Cool, Tamarac, and another which escapes my memory, is that these smaller bladed units behave more like an exhaust fan. Most of what I looked at boasted quiet operation and I can see how the ducted Quiet Cool could achieve that. But what steered me away (besides the cost) was an expert opinion that basically stated this, “If you want the quiet operation and ease of installation of the ‘boxed’ in units, you need to be prepared for less air movement when compared to the vintage style WHF’s. They are nice units. But if you want that hurricane force wind that slams doors, pulls curtains and drapes horizontal, and will suck the cats up to the ceiling, you really got to go with the large blade units.” This a parphrased quote, but you get the drift. I wasn’t necessarily talked out of the newer concept for marketing reasons. I was just given some good info based on my expectations. Personally, I would have gone for the Quiet Cool if I was looking for more gentle breezes, since that design appears to have virtually eliminated any noise just because the fans are located at the end of a duct and mounted up off the floor of the attic….FWIW.

    Comment by Jeff — February 19, 2012 @ 10:52 pm

  13. Yeah, I could see how one of those ducted units where the fan is located far from the ceiling would be a little quieter, but as you said, they simply don’t move nearly as much air as a 30″ or 36″ unit. I just chatted with the president of a company that manufacturers those ducted units, and he couldn’t believe that I got 6000cfm out of my fan. His top end unit does maybe 3500 and its over $2K. I’m not downplaying his units, because they are really nice, but $200 vs $2000 is a big price to pay unless you absolutely need quiet. I personally like the white noise, and more importantly, I like prying my cat off the fan louver :).

    Comment by Matt Warshawsky — February 20, 2012 @ 1:29 pm

  14. I should add, on the actual topic of this page, that I’m planing on insulating my big fan a little differently. My attic is less than 4′ tall at the peak, and I want to be swimming in blown insulation when I’m done. I’m obviously going to have to put a fence around the fan to keep the blown insulation out of it, but I’m either going to then put a mechanical top that hinges open, or simply put an insulated panel that mounts on the bottom side (in the hall).

    The panel idea is certainly easier to do, I’d just build up some space by screwing 2×4’s into the ceiling and walls with t-nuts premounted, then bolt the panel in when I need it, but a) this is probably ugly, and b) requires me to find a place for the panel for the 4 months I use the fan.

    The mechanical hinging door idea of course comes from the self-insulating fans described in the article. This idea became a reality when I discovered a low cost place to find linear actuators: $100 will get me a 6″ actuator with enough force to open a door and pull it shut, and with built in limiters, all I have to do is get some power and a switch wired up. It’ll be a few months before I have it in place, and if I remember, I’ll try and post photos…

    Comment by Matt Warshawsky — February 20, 2012 @ 1:37 pm

  15. Matt….yeah…good to get back on topic. But the side discussion could play into just HOW we try to insulate our units. I just picked up my 5700 CFM Air Vent (for $89..woohoo) today and really ended up in this blog on a search for a way to insulate my new fan. I have piqued my neighbors interest on the subject as well…since he has a similar fan. I like the simple design of the author’s project, and may very well revert to that. However, I also liked the “Fansulator” as seen on Youtube. Plugging in the website info given in the video proved to be a dead link. But it doesn’t look so difficult to build. It incorporates a damper like action on the lid of the insulation box only using the force of the air from the blades….another advantage to the high CFM’s. The authors design could perhaps be modded for this set of ‘doors’. But since you guys are discussing R value as well, it’s probable that will suffer even more with a lid that doesn’t quite seal. I like the concept, though. And maybe used in tandem with a seasonal louver cover on the downstairs side, it just might be the ticket.

    Comment by Jeff — February 20, 2012 @ 2:39 pm

  16. Jeff, I considered doing something like what they did with the fansulator (not knowing anything about that particular product). I was going to use spring hinges to hold it down and use the fan’s power to push it up, but truthfully, I’m concerned about what that will do to the pressure differential (and thus the ability to pull air out of the house). My other problem is that the doors would likely hit my rafters.

    I am most likely going with the actuator method. That way also I can ensure that there is a reasonable down force on the doors to give a good seal. Plus it gives me an excuse to play with an actuator.

    Comment by Matt Warshawsky — February 20, 2012 @ 4:40 pm

  17. So I wrote this in 2009 and three years later my $20 … well, actually $40 … project is going strong. R value is important, but by far the most important thing to get right first is a good air seal (I made a comment above noting that a return blower-door test found I needed some additional sealing).

    During the time I was actively writing this blog, and then at Energy Circle, I found that there was always a lot of healthy discussion about which way was best or better, but as often as not, it was any way that gets the ball rolling. Over-analysis can just make a project take longer than needed. Just sayin… :-)


    Comment by Tom Harrison — February 27, 2012 @ 2:23 pm

  18. True Tom, but its often good to at least have a few ideas in ones head, even if you don’t plan on implementing them all. People have different situations, and certainly hearing about things that didn’t work well is helpful.

    I certainly wish someone had mentioned the problems with tankless water heaters before I installed one. Sure I’m saving on water bills, but my washing machine doesn’t play well with it, nor does a whole house one do well for hand washing, so now I’m going to have to put three point-of-use tankless in, and the rather expensive whole house one is just going to do showers.

    Personally, I can’t implement your method for insulating the fan because my attic is tiny, so I wouldn’t be able to remove the type of cover you have, and I have blown insulation and tramping over the insulation to remove the cover would create a different set of issues.

    Comment by Matt Warshawsky — February 27, 2012 @ 2:41 pm

  19. Figured I’d chime back in here. I would be interested in hearing about your damper/actuator idea Matt. And I am in the over analysis stage right now. Since I haven’t installed my fan yet, but am anxious to get the hole cut, I still need to contruct a similar box as in the original post. I’m one of the lucky ones who has a semi finished attic. A solid tongue in groove floor and plenty of space to move around is making it difficult to pick a good location for this fan. When I saw the author’s pink box sitting not so dead center and closer to the soffit, I thought, “Hey…that’s what I was planning to do.” I wanted it out of the way from the center of everything up in the attic. But now through some major over analysis, I’m backing away from putting it so close to the soffit part of the roof. I’m really trying to find a compromise here and then I find that I have to cut through 2 joists instead of one to put it in the next best location relative to asthetics for downstairs. So I guess I was wondering if that fan location in the picture above is causing any back feed into the fan blades. And second I was wondering how people are dealing with joist cutting. The fan instructions say to cut joists and build a box to support the cut joists. And on some sites, I’m reading that under no circumstances you are to cut joists. My neighbors fan has the joists cut out and his roof didn’t fall over. Anyway, I know this is an insulation blog. But I was hoping my q’s are on topic enough to get me to the point of making my insulation cover. I know that’s a little underhanded, but hey…it’s worth a shot. Thanks.

    Comment by Jeff — February 27, 2012 @ 6:27 pm

  20. If you have easy access to the attic, I would just do what the original article described. Spending the time and money to do an automatic damper doesn’t make sense really since you’d only be climbing up into the attic twice a year.

    Placing it close to the soffit probably isn’t a problem. I have a 4/12 roof with 24′ span which means I’m only 4′ at the top and the fan is off center, so there is maybe 2′ above the joist (bottom of fan) on the lower side. I don’t have backflow issues that I know off. I would imagine that not having sufficient vents in the attic would be more of an issue as this would increase the pressure in the attic.

    As for cutting joists, that is largely an engineering thing and there are a lot of variables here. I cut one joist, but I have kind of an unusually built house. There are usually two issues with cutting joists: 1) your ceiling will sag. This would be a problem if you cut a joist in the middle of a room for example. Since mine was in a hallway running perpendicular to the joists and the hallway walls were, due to the way the basement is framed, essentially bearing walls, this was no issue. 2) the roof will sag and the outer walls push out. Personally I can’t imagine how this would happen cutting just one joist, but I’m not an engineer. I also have cross bracing in the attic that helps with this, creating more triangles and more stability.

    At a minimum, I would put a cross piece connecting the two complete joists and tie the cut joist into this. Better would be to double these cross pieces and use joist hangers. Just look at how one frames up a stairway.

    Comment by Matt Warshawsky — February 27, 2012 @ 7:24 pm

  21. Hello All:

    Great thread.

    I am looking into the whole house fan idea right now and wanted to get the experts take on it. (That’s you guys!)

    I live in the SoCal desert where summer temps can reach 120f. Hot! Winters are mild, in the 70s. Coldest it ever gets is in the 40s at 3am in the dead of winter. (If you can call 40s “dead”.) :-)

    This whole idea started when I considered insulating my uninsulated garage. Quote was $411. Instead of doing that, I’m now thinking of having the whole-house attic fan installed. I got a quote of $550. I need to check the type and quality of fan to see if it’s a good price or not, of course.

    My roof is concrete tiles, typical southwest style.

    If I’m going to get a fan, I want my 91 pound dog sticking to the ceiling, like Jeff suggested his cats would be. I don’t want horribly loud noise of course. So, I get that it should be mounted OFF the floor, correct?

    House is just over 3,000 square feet.

    Could someone recommend a fan brand and model for this application? And possibly give any advice for my situation.

    Also, is 1 fan enough for me? The attic–in the summer–is so hot, I have seen the devil himself up there sharpening his tail.

    Thanks so much!

    Comment by Eric — June 14, 2012 @ 6:16 pm

  22. Eric….

    My fan is made by Air Vent. They have a very comprehensive site with all their products and a whole slew of PDF’s about proper fan sizing and attic ventilation. The information there is invaluable if you are considering whole house ventiilation. I think it’s a good place to start since there are additional things to consider when planning for a whole house fan. At 3000 sq. ft., you will likely need a 36″. Whole house fans need to have enough “free air space” (attic vents) to the outside in order to freely move the air up and out of your attic. You may or may not be aware of this and it’s really common sense. But you may find yourself in a situation like I was in where I had to increase the attic ventilation in order to accomodate the air flow of my new fan. It was on Air Vent’s site that I discovered that my attic was not properly ventilated in the first place. I had a ridge vent and nothing else. I actually found out that my ridge vent was not doing anything for my attic ventilation. Seems like in the old days (back in the 50’s), the mindset was to seal off the attic rather than ventilate it.

    In any case, even if your attic does have proper ventilation now, you will need to make sure it can handle the addition of a WHF. Air Vent’s site is a pretty good tool and I highly recommend checking it out.

    Comment by Jeff — June 14, 2012 @ 9:02 pm

  23. But I also wanted to add that after I added the much needed soffit vents to make my ridge vent actually do something, that the ambient temperatures in my attic have dropped considerably…even with my whole house fan off.

    Comment by Jeff — June 14, 2012 @ 9:05 pm

  24. Eric —

    First, I think the aerodynamics of cats and dogs differ sufficiently as to mitigate your safety concern. I would be slightly concerned about uncaged birds (unless they were also 91 pounds, in which case I would be concerned about the fan). :-)

    So here are some things to consider:

    • The Tamrack fan I linked above is expensive, but quiet, but one is not likely to be sufficient for your case
    • The inexpensive fan I bought at Home Depot does the trick, but it’s not quiet; because it has a larger motor and is mounted to the framing of the house, you know when it’s on. We still love it, but could do better.
    • I have seen fans that mount inside the attic itself, near the exhaust window; when on they open the louvers and draw air through the hallway ceiling and out; they can be powerful and very quiet.
    • Keeping the attic itself properly exhausted is different than a whole-house fan — keep the attic as cool as possible and your home will not get as hot. The whole-house fan draws cooler air from outside through open windows to cool the house … which only works if it’s cool enough outside. 120°F seems hot to me (just sayin’) — maybe it gets cooler at night?
    • The downside of a whole-house fan is that you are cutting a hole in the house “envelope”, reducing the air sealing and insulation; this is why I built my box (for the winter), but it’s a bit of a trade-off in the summer, since we only run the whole-house fan in the evenings

    Hope I haven’t muddled things.

    Comment by Tom Harrison — June 14, 2012 @ 9:32 pm

  25. Tom,

    What you’ve done is EXACTLY what I’ve been planning for years. My only different idea would be leaving the two top panels of pink insulation (in your picture) “hinged” on one side with duct and/or foil tape so that the “doors” would opened by pressure when the fan was on and then fall back into place when the fan is switched off. In central Texas, there really isn’t aren’t clear seasonal times to ‘remove the box’ or ‘install the box’

    Any thoughts or suggestions?

    Thanks. Great post!


    Comment by Stewart — August 28, 2012 @ 2:15 pm

  26. Hey guys,
    I’m planning on building a “winter” box but wanted to through in my lessons learned to either help you of spark some additional ideas.
    I installed a WHF about 10 years ago for the same reasons; fresh air, cooling the house w/o using A/C, reducing costs, etc.. All things considered, I have no regrets. I chose a 30″ unit because at the time I had to consider a) ease of installation and b) square footage (about 1500). I tried to locate the fan closest to the center of the house so that the distance from each bedroom was approx equal and there was minimal obstruction for the air to travel from the downstairs to the exhaust port. So upstairs in the hall, its located in such a manner that the air flow is relatively balanced flowing from all directions, although I do have to close a door a bit from the nearest bedroom. I also built a plenum (wooden inlet duct) to extend the distance the air has to travel before in reaches the fan blades. Thus the frame of the fan assy rests approx 12″ above the ceiling. (suggested by the manufacturer)
    Since I wasn’t too anxious on cutting a joise, I located the fan so that the joise is aligned along the centerline of the louvered grate. Anyhow it looks and performs great.
    To cover for the winter, I saved the cardboard box the fan assy was packaged in and reused the lid. I sprayed contact adhesive to all exterior side surfaces of the box. Then cut bat insulation and wrapped the box lids sides to provide approx 3″ of insulation. I also wrapped duct tape bands around the perimeter to secure the pats in case they separated due to gravity. I then added insulation to the top.
    In the spring, I just removed the box from the fan and set it aside until the fall.
    Now I think I have to do something a little better because as I walked in the hall the other day, I couldf feel a draft.
    I’m planning to use either 2″ foam board (R15) with additional insulation added or use styrafoam (cheap boards) and bat to build insulated panels. I then would construct a box. I estimate the R value would approach R-20. I’ll make that decision when I check availability and cost of materials.
    The idea about the panels on top closing and opening is a great idea but way too complicated for this application. I agree, you don’t want to cause any additional back pressure that would affect airflow . And using actuators requiring power, wiring, switches is only going to add cost and most likely headaches. Why not install counterweights on the top panels that allow the panels to open when the fan is on and close when it’s off? Sort of like the louvers on the grate.
    Again, I think it’s a good idea and I just may give it some additional thought because when it is extreamely hot during the summer and the A/C is on, It would help keep the upstairs cool.

    Comment by Alan — January 7, 2013 @ 6:45 pm

  27. Alan —

    While R-value is important, in my installation it was getting the air sealing that turned out to be the real key.

    After my first pass, which I showed in the photo here, I realized there was a lot of air leaking through the attic floor boards and the various connections to the plenum leading into the house.

    I put down a nice flat surface of pink styrofoam board and sealed it with spray foam. The spray foam is great because you can get it in all the cracks and crevices — and at least in my installation there are a lot of paths for air (including outside of the fan box and frame). I backfilled the open areas around the box with fiberglass insulation. Air sealing solves the more significant problem with cutting a hole in the envelope of your house.

    Anyway, I sealed everything up and now, every fall just drop the box shown in the picture on top of the flat surface and tape box to flat platform with duct tape. In the spring, remove box and all is well.

    I agree that the self-insulating fans are probably not worth the effort in many climates — here in Boston, it’s pretty much either cold or not. In some areas, the insulation when closed is mainly for when it’s hot during the day and cool enough at night to run the fan.

    Comment by Tom Harrison — January 9, 2013 @ 9:09 pm

  28. I guess I should have followed up earlier, but here it is…
    I made a box constructed of 2″ foil faced styrafoam board purchased from Lowes. The foiled surface faces the inside and the “panels” and joined with foil taped, inside & out. The box encloses the fan/motor assembly and rests on the face where the plenum meets the fan base. Upon initial fit, I “pounded” the box to ensure a relatively tight fit is obtained and any obstructions or interference cause by the centering blocks that were used during initial installation were impressed into the foam edge of the box. I then removed the box and removed a little foam material and covered the fan assy. The fit is great and if there is any crevises, O can’t detect them nor feel any drafts when checked.
    Total cost was about $35. I’m very happy with this and hopefully should last another 15+ years. When I walk under the fan in the hallway, I no longer feel a draft or the cold. So far so good!
    I’m not sure how to post pics otherwise I would.

    Comment by Alan — March 27, 2013 @ 11:47 am

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