Whole house ventilation?

[cgallery]

I have an access panel that provides access to my attic. It is (maybe) approx. 32" square, and is located in the ceiling of my bedroom (three bedroom, two story house).

When I had the roof replaced, I had three vents cut into the peak of the roof. There is no other venting in our attic, that is the way these houses were built.

My thought is that I'd replace the plywood access panel with one made with a window screen. And that if I left the screen in, heat would rise and it would help to cool the entire house.

But now I wonder what happens during the day. I've read about some people closing all the doors/windows during the day to keep it cooler inside the house. So maybe I need a way to close the screen at times. But if I do that, then the attic gets very hot because there are no other vents.

Any suggestions? I'm thinking of just making a screen and putting it in place and seeing what happens. Any ideas of what kind of fans I could mount in a panel that would move some decent CFM? Do I have to worry about horizontal use?

[jackellis]

If you place a screen over that opening, you will create a chimney that pulls cool air into the house as hot air in the attic attempts to escape from the vent. That chimney works on hot days but it probably works even better on cold days, when it will pull warm air right out of your house and draw in cold air that has to be heated. Make sure you can seal the opening in winter.

I suspect the area of the three vents together is probably less than the 1000 or so square inches of opening into the attic. If so, putting a fan in that opening isn't going to help much because there will be too much resistance as the fan tries to push air drawn from the house out through the roof.

Depending on how your house is built, you might consider adding a couple of gable vents so that air you push into the attic has some place to escape. Then, I would run the whole house fan to cool both the house and the attic (almost so cold you can't stand it) in the evenings. It is especially important that the roof and ceiling structures cool off, because it is the heat they absorb from hot air in the attic that heats up your house during the day and at night. In the morning, close all of the windows and make sure the attic fan is off. If your house is reasonably well sealed, hot air won't get in and the cool structure will help keep the temperature down until it's cool enough inside to start the cycle again. It's known as taking advantage of thermal mass and it's the principle that keeps massive stone church buildings and adobe homes in the southwest cool during hot summer days.

We use window fans instead of a whole house fan and even on the hottest summer days (95+), it typically stays below 78 degrees, unless we have an extended heat wave.

[cgallery]

Thanks Jack. Yeah, I was thinking of just setting the solid (insulated) panel up in the attic while I'm using the screen. It isn't hinged or anything, it just simply sits on a frame in the ceiling and pushes right up and out.

I'm on my way out to purchase some screen material and I'm going to give a screen a shot and see how it works. It is supposed to be a high of the mid-60's here the next few days, so probably a pretty good time to experiment. This because, it typically gets quite warmer on the 2nd floor. I think it is because of all that heat trapped up in the attic.

[Tom Slick]

I've also thought about leaving the access open to get the chimney effect. What I've found is the house begins to smell like the attic; dusty and like insulation.

[jackellis]

One important thing to know when you're using fans is that you want them pulling air through the house rather than trying to push it into the house. Our window fans are right up against the window and direct the air outside, thereby pulling in fresh air. My wife used to have them turned around, which was not very effective.

[cgallery]

I've also thought about leaving the access open to get the chimney effect. What I've found is the house begins to smell like the attic; dusty and like insulation.

I thought about that today when I was measuring the opening for the screen I'll make. It is dusty up there, but at least it doesn't smell badly.

I guess making the screen will cost about $5 so worth a shot. If there is significant dust/odor, I can always replace it with a fan that has a door I can close when I'm not running it.

[JackimoT]

If your looking to cool the house down and you have openings already cut in your ceiling and attic than I'd suggest a whole house fan, like one of these: http://www.shophmac.com/fans/whole-house-fans.html They'll help keep your house cool and cost a lot less electricity than the AC. Sounds like the way to go given your situation.