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.

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!

Stewart

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.

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.

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!
Eric

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.