O.T. Are Attic Fans Effective?

[Derek Arita]

I was thinking about installing a solar powered attic fan. In doing some research, I found an article that basically says, don't! The article states that attic fans draw cool air from the house to cool the attic and they can pull dangerous gases from appliances like water heaters, therefore, they aren't an effective way to help cool your house. He also says good insulation will do the job just fine.
I'm sure that there are some of you that are much more experienced than I in this field and I'm hoping that you will chime in here. I live in So Cal, where heat is an issue a good part of the year. Thanks for your collective wisdom.

[Kyle Kraft]

A whole house fan mounted in the ceiling will indeed pull air through the house and into the attic...but the last time I checked that was the whole reason for installing one . We use 'em in Michigan to cool the house on milder summer days to save on the A/C bill.

The only solar attic fans I'm familiar are basically a powered roof ventilator. If you have adequate perforated soffit on your house and other roof vents, and don't terminate any bathroom fans directly to the attic, then I can't see this being a problem...just my $0.02.

[Lee Schierer]

What type of fan are you talkning about? One that pulls air from teh attic to keep the attic cool or one that exhausts air from the entire house?

A fan installed in teh attic for cooling the attic space cannot draw air from any of the appliance exhausts if they are properly piped and sealed. You must have a perforated soffet or other air inlet into the attic inorder for this type of fan to work.

An attic house exhaust fan like any other must have a place to draw air from. If you are pulling air out of the ceiling with an house exhaust fan, the make up air has to come from somewhere. You also have to give the air a way out of the attic. If you have gas appliances/heat or fire places and the doors and windows are all shut, then the fan will pull air back down the stacks and chimneys, which is not good. the same is true for bathroom exhaust fans and range hoods, though they are usually less powerful.

[Jeff Horton]

Bet this gets moved and quickly!

The article states that attic fans draw cool air from the house to cool the attic and they can pull dangerous gases from appliances like water heaters, therefore, they aren't an effective way to help cool your house. He also says good insulation will do the job just fine.

Are you talking about Whole House attic fans? Being solar powered I am assuming you are talking about a fan that is made to move air through the attic and not the house.

If you talking about an attic fan that sounds like the article is full of holes. If you talking about a whole house fan than maybe, but a there are a lot of maybes there.

As an attic fan, it's probably not going to cool your house one bit, nor the attic for that matter. But it would keep moisture from building up in the attic but good ventilation will do the same thing too. I have never inspected a house (in the south) that has a moisture problem in the attic unless the there was a leak. I installed powered fans in mine but I am not convinced they really do much except blow hot air around. There sort of like a cure for a non-existing problem.

[Sam Chambers]

If you're talking about a "whole house" fan, they do work. I had one in my old house. When I was single and traveled, I'd turn my A/C up to about 85 before I left, or turn it off alltogether. When I returned, I'd open the windows, turn on the fan, and it'd cool the place down in no time. Then I'd turn the A/C on.

If you're talking about an attic vent fan - and I suspect you are since the one you're taling about is solar - they also work. I had one installed a few years ago in my new house, to cut down on the heat in the attic and allow the upstairs A/C to be more effective. I'd say it made about a 5 to 7 degree difference in the temperature upstairs.

[Rob Russell]

I'll comment and I think summarize what's already been posted.

There are 2 types of fans you can install in an attic - a "whole house" fan (WHF) and and "attic vent fan" (AVF). The fans serve different purposes.

The WHF is meant to cool off the house. It's a big fan, is typically mounted horizontally in the center of the house and, if on the second floor, near the stairs. The fan blows up into the attic. You open windows, turn the WHF on and the fan effectively sucks outside air into the house. We don't have central AC but do have a WHF. It's effective on all but the steamiest days and even then at least keeps the air moving.

The AVF is meant to exhaust hot air from the attic. They are typically mounted on a gable wall and blow out. Some AVF's mount inside the attic blowing out the gable vents, some replace the vent. The theory with the AVF is that by getting the really hot air out of the attic, you'll reduce the amount of heat that radiates down into the house. I can tell you that, last week when we lost power and couldn't have the WHF running, there was a noticeable amount of heat radiating down from the second floor ceiling.

Both types of fans require venting in the attic. WHF's need a place for the air to go. IOW, when the WHF blows up into the attic, you need vents for that air to escape out. AVFs need vents too, but for a different reason. The AVF needs a place for makeup air to come from and you don't want that place to be the living space - you want it to be outside air. That way you're not sucking conditioned air out of your house.

Rob

[Al Willits]

To make it easy, if you run a whole house fan and run gas burning devices, you could be running the chance of killing you and whoever else is in the house, these fans, fireplaces and to tight houses, kill people each year from CO poisioning, be careful, very careful.

Al

[Mark Rios]

Lee and others have the right idea. A "whole house fan" and an "attic fan" are two different appliances. However, they can be used in conjunction with each other to very effectively help cool down the house.

The attic fan is usually placed at one end of the attic at a gable vent in a house with gables, or at roughly the highest point of the roof in the case of full hip roof. It removes the heated air in the attic space. There are requirements for having the appropriate amount/size of vents, whether they are gable vents, eave vents, soffit vents, dormer vents, etc., for the attic vent to draw from. There is a ratio of attic space (in the form of cubic feet) to vent size, the vents needing to be able to draw air from outside of the building, that is a minimum so that the fan can do it's job.

A Whole House Fan is generally used to rid the house of the warm/stale air one confronts when one enters the house after the house has been closed up for an extended period of time, like during the day for example. After you get home, you can crack the windows, turn on the Whole House Fan and in aproximately ten or fifteen minutes (depending on the size of the house) the whole house has had a complete air exchange, hopefully with cooler air from outside. The temperature inside a house can be feduced by 10 to 20 degrees just by doing this. Then, after turning off the Whole House Fan, closing the windows and turning on the AC, the AC doesn't have to work as hard to cool the house and the house cools down quicker and uses less energy. I'm sure that a Whole House Fan could also be used alone to simply draw air from throughout the house, through windows and doors, and just use the breeze to cool the occupants. The main thing is, as has been mentioned, the Whole House Fan needs to draw air from OUTSIDE through windows (and doors if desired).

These types of fans are a big consideration here in CA. So much so that there are rebates from the energy companies for these kind of appliances.

Now, before anyone gets all riled up and wants to startup something , this is just a GENERAL use guideline, specifically related to me both verbally and in writing by the engineer lady who did the energy calcs for the last house I built. I'm sure that others have used these appliances in other fashions and have had other results with other applications. Your mileage may vary, as they say.





EDT: I'll edit my first sentence to read "Lee and others...". Looks like I took too long to write my post.

[Chuck Saunders]

I would have to disagree with the position that whole house fans cause concentrations of CO to build up in the living space. Considering that WHF are typically run in the summer months thus the chances of your furnace or gas fireplace being in operation is less likely, that leaves your gas dryer, stove and hot water heater as the working appliances. Stoves are not vented as a general rule. Considering the cfm of the WHF and the requirement of windows or doors being open to allow makeup air for the WHF, I do not see the opportunity for the CO to concentrate.
Chuck

[Al Willits]

Sorry, was multitasking at the time I posted.
Summer isn't a problem, but we have cases of fans running during the winter and people dieing of CO, these fans will out draw the water heater/furnace and pull combustion air back into the house, the next time the wh/furn burns this air it creates CO.

This has happened several times in the last few years, fwiw

Al

[glenn bradley]

I wouldn't go the expense of solar (a good one that is) version. It would take too long to recover your costs through utility savings. I have added gable fans to the last two houses I've lived in. The results were dramatic temperature-wise and dollar-wise. I California we shoot the fan out the downwind facing gable. There should be an upwind facing gable, soffit grates or whatever method of attic area vetilation is to code where you are. Again, bear in mind that when most Californians say 'attic' they mean the crawl-space above the ceiling and below the roof; not an area that could become a spare bedroom or some such. hope that helps.

P.s. pulling hte air in one end of the attic and shooting it out the other does not pose a problem for your stove, etc.

[Art Mulder]

Derek,
I put in a roof-mounted powered attic ventilator this spring. I discussed it in this thread: http://www.sawmillcreek.org/showthread.php?t=39104

We're happy with it, and I think it definitely makes a difference.

That said... I live in Southern Ontario. That is a radically different climate from Southern California. I would urge you to also look for advice from someone local.

...art

[Fred Woodward]

I'm thinking you are talking about true attic fans to cool the attic space and not WHF.
Not knowing where you are located, this may not be applicable to your situation. I recently had the roof repaired from hail storms last year. I looked into "attic fans" of various sorts to help cool the attic space (not a living space) and determined that I would be better with ridge vents in the roof rather than a powered fan. I already had vented soffit.
I had ridge venting in my house in Florida and it had helped keep the utility bill lower as compared to other homes of same size in the same area.

I had not been in the "attic" space much since the ridge vents had been installed till last week or so when I was looking into pulling new electrical circuits into my shop (garage) area. Well, it does seem to be much cooler in that space now. How much? I did not measure......but I will.
Here in Texas, I have measured the attic temperature during the Summer at mid afternoon and seen it to be as high as 150F in the attic. I know it was not that hot in the attic last week, maybe it was 100 or so. Still, it was signicantly cooler. I will take some measurements this afternoon.

I do know that since the ridge vents have been installed, my utility (electric) bill has dropped about $50-60/mo. for the Summer months compared to the same months last year. No other changes to AC, thermostats, habits and the temperature has been higher this Summer than last.
Well worth it to me. The ridge vents added about $400 to the roofing job.

[Derek Arita]

Thanks for your replies. I am talking about attic venting fan, not a whole house fan, although I have one of those as well. I believe the article was saying that unless your attic space is completely tight from your living space, which in my house it is not, then the attic vent fan will not only vent heated attic air to the outside, but also cooled air from the living space, via electrical sockets and other wholes in the walls. Note, I do have soffet vents and gable end vents as well. Understand, this was an article I read and not my own personal opinion. I'm asking this question here because I'm sure you guys know more about this than I.

[Joe Pelonio]

Running a powered fan like that is going to use a lot of energy that could be used to run an air conditioner. When we lived in CA I installed 2 turban ventilators on the roof, on the back side so not visible from the street.
I also installed gable end vents sized to provide enough fresh air intake.
Without wind the heat rising causes them to spin, drawing in the cooler outside air and expelling the hot attic air. On a windy day they spin faster and move even more air. In the last house we were in I also moved the fresh air intake for the furnace to the finished basement which always stayed cooler. With the turbine ventilators, keeping the windows covered when the sun was on them, and the furnace running on air only (no a/c there) we could keep it at about 74 inside on a 100 degree day. The main advantage to cooling the attic though, is to prolong the life of the roof. On high humidity days it will also keep the attic and underside of the roof drier.