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.
Whole House Fan, or House Hole (click for full size image)
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
Before
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.
After
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
All 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 :-)
The most efficient heating and cooling systems are useless without proper insulation.
Comment by Charles — September 26, 2009 @ 7:34 pm
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
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
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
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.
Tom
Comment by Tom Harrison — March 22, 2010 @ 12:24 pm
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
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
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
Hey Matt –
Thanks for your comment. Do you remember the brand name of the fan you purchased? I used to work at EnergyCircle.com 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
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
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 https://www.pesstoreonline.com/products.php?cat=7&pg=2
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