Installing fans on gable vents?

Powered attic fans have been shown not to be cost effective in homes with air conditioning. Ask you electric utility.

Installing two passive Turban (Turbine) Vents in my roof accomplished the same end for (LOTS!) less expense to purchase and operate.

We were seriously looking at the notion of putting in a couple of powered gable fans, but the hassle of mounting them, wiring them and cost of operating and maintaining them quickly ruled them out.

The two Turbans have lowered the summer-time attic temperature from the

From my personal experience, don't bother.

Art, the problem is the things take power to run, and they run a lot.

The studies I referred to were done at what whas then the National Bureau of Standards (now NIST). They found that the power used by the fans exceeded that saved at the AC compressor on an annual basis. One problem is they are usually controlled by a thermostat in the attic, so they run any time the attic gets hot, even while you are on vacation. My neighbor has one so I have first hand experience with that issue. And it makes more noise than her AC!

I'm glad you got rid of them!

Ed

As far as I've read, some towns feel that they are a fire hazard as they will pull a fire right up to your attic.

After 8 years as a volunteer firefighter, I know it's standard procedure to chop a hole or three in an unvented roof to get the trapped heat and gases out so the fire can be fought.

What powers those things, to make them spin. Is it the wind, because I live in a valley and don't have much wind. If it is the rising hot air from the attic, what is the point of its spinning?

Meirman

If emailing, please let me know whether or not you are posting the same letter.

Change domain to erols.com, if necessary.

I believe studies have shown whole house fans, drawing air from the house and out through the attic, to be cost effective, unlike powered attic fans which draw air from the outside, which are not. I'm not sure about running it all night though. Unless you have a lot of mass, e.g., uncarpeted concrete floor, tile roof, etc., it seems that thisngs are going to be about as cool as they are going to get after a few hours. PErhaps a timer could be used to turn it on only when outside air is coldest... midnignt to 6 AM.

Ed

">

George,

Do you have any evidence that " ...but if it is not adequately vented and the fans make it so, then the fans will be economically justified?" As I said, I have seen reports of detailed studies showing they were not, so if there is newer and better evidence to the contrary, as opposed to someone just saying it's so, I'd like to see it.

BTW, my original comment about what the utility company would say is assuming that they have an energy conservation mandate from state and local authorities. That is, in many states utilities are legally constrained to NOT give out advice that will run up your bill. If not so constrained, and willing to deceive in order to improve their bottom line, they will love powered attic fans.

Ed

: Meirman :

Convection "powers" them. Heat rises and exits through the vent. The turbine blades that make up the "turban" are rotated by the rising heated air and the pitch (of the blades) accelerates the air flow out of the attic. (The "turban" also has the added benefit of keeping rain out of the attic.)

Not in front of me, but I use to accumulate a bunch of energy conservation stuff. I've seen the 10 degree temp lowering (between adequate and inadequate ventilation) figure in Electric Utility pamphlets and in U.S. government publication. That stuff is somewhat old. The difference in power usage is so high (170 watts (fan) compared to 3600 watts (AC)) that if the fan only reduces AC running by only

jagerEd wrote:

Why don't you get a solar powered fan that will only run when the sun is strong and you won't have to worry about your electric bill. You only need one to draw out the hot air.

We use it instead of air-conditioning. It gets hot and humid where we are quite often. On those nights, you want the breeze from the fan in the evening hours and into the night. Depending on the temperature fall and on whether I feel like getting out of bed at 2 or 3AM, it sometimes gets shut off then. Other nights it runs until I rise a

By 7AM during the summer it is already starting to heat up so it needs to be shut off and the windows closed up to preserve the cool air. In a well insulated house, this keeps it comfortable most of the time aside from a few hours in the late afternoon on the really hot days. Those days you just open it up and turn on the fan to enjoy a little moving air.

As a side benefit, a whole house fan makes one heck of an exhaust fan when you burn something on the stove :-)

Bob

How can it be both powered (spun) by the air flow and accelerating the air flow? Is it taking energy from the air or lending energy to the air?

If it were to do both, doesn't that sound like a perpetual motion machine?

Maybe turbines slow down the air less than ridge rails, and the only benefit of a turbine over a hole in the roof is that it keeps the rain out (while slowing the air down less than would be the case with say, a roof fan housing without the fan. Where the air has to go up, then sideways, and then up again.

Meirman

If emailing, please let me know whether or not you are posting the same letter.

Change domain to erols.com, if necessary.