[Splais]

I just ordered a solar powered attic fan for our house and now I think it may have been a huge mistake. I reading a lot of stuff on other forums thst says attic fans are not a good idea unless you have excellent airflow from soffets and have a ceiling that is 100% sealed air tight. Otherwise you are just sucking all the cool air (and moisture) out of the house and into the attic.

Well we have a house built in 1947 that is not even close to having the ceiling sealed. On top of that most of the soffet venting is probably plugged up with old insulation. We have a gable vent at one end of the 1200sf single story house with about 5' of attic space at the peak. Blown insulation was added to the attic just before we bought the house a year ago. My plan was to put the solar attic fan at the other end of the house from the existing gable vent.

Can anyone who actually knows about this stuff tell me if it would be a bad idea to put in an attic fan under the conditions described.

 

[user_12345a]

don't know this stuff more than u do but your concerns are totally valid.

for soffits i think you're supposed to install baffles to prevent the clogging.

A solar venter may not be very powerful; can't imagine one moving more than 50 cfm or so.

Specs may say otherwise...

http://www.deelat.ca/electrical/ren..._id=D1143119&gclid=CPfO9MDDzswCFRIoaQodhn0Hzw

1650 CFM running 15 w -> no friggen way even with a super-efficient motor.

 

[beenthere]

If the attic fan can exhaust moe air then the gable vent allows in, it a bad idea.

 

[supers05]

...
1650 CFM running 15 w -> no friggen way even with a super-efficient motor.

Technically it's fan assisted not fan powered convection. There's already a great deal of air movement in their laboratory testing. However, unless the OP has a very similar environment as their lab, it isn't going to happen. (even then, those numbers at exceptionally high)

BT is right. You can get to the soffit vents with the help of a ladder. You can then clear them of insulation. Then count the number that you have and their size. Add the size of the gable vent and someone here will be able to calculate the available airflow.


Cheers!

 

[gregzoll]

More of a band-aid than anything. You need to find out what the temps are on the hottest day and go by that for how you need to cool.

I went through two motors on the one I had installed, until I could get the proper venting in on the sides of our Bungalow. Originally it was just two windows that never opened and Ridge vent on both sides.

 

[Bud9051]

Hi Splais,
As others have said, open up those soffits as one gable vent would limit the air flow. It would also cause the fan to draw more from the house.

As for sealing between the house and the attic, do you have a basement or is it a house on a slab?

Bud

 

[user_12345a]

Technically it's fan assisted not fan powered convection. There's already a great deal of air movement in their laboratory testing. However, unless the OP has a very similar environment as their lab, it isn't going to happen. (even then, those numbers at exceptionally high)

that is so deceptive.

 

[gregzoll]

Bud the problem is that a lot of the older homes do not have soffits, unless you had the roof reframed during a roofing to add them.

 

[Bud9051]

Greg, I agree that many older homes do not have soffits and for that there are other solutions. Here, it sounds like the op has soffits and maybe some soffit vents:
"On top of that most of the soffet venting is probably plugged up with old insulation."
But that does need to be confirmed.

Bud

 

[AlleyG]

I went from having soffit vents and large gable louvers (4) total, to a ridge vent, along with adding more soffit vents. It is noticeably cooler up there.

Even before I added the ridge vent, just adding more soffit vents while preparing for the roofing job made the attic more comfortable. I ended up covering the gable louvers.

I would clean out all the soffit vents, then measure the temp. A before and after compare would be interesting. Adding a ridge vent would be the most beneficial, if feasible. Usually it's done during a roofing job.

Gable louvers are useless unless it's windy, and I have not heard one good thing about solar powered fans.

Al

 

[gregzoll]

Greg, I agree that many older homes do not have soffits and for that there are other solutions. Here, it sounds like the op has soffits and maybe some soffit vents:
"On top of that most of the soffet venting is probably plugged up with old insulation."
But that does need to be confirmed.

Bud

Actually I think that the OP may have the terms mixed up. We would need pictures to back it up.

 

[Bret86844]

What is the make/model of the fan you bought? Solar powered attic fans don't typically move lots of air. I think you are thinking of whole house fans that get mounted in the attic but actually exhaust air from the house.

 

[Splais]

it's a Natural Light SAF-24 Watt Solar Attic Fan, 1340cfm in up to 2100sf attic. No it is not a whole house fan.

 

[user_12345a]

To push that kind of cfm you would probably need at least 200 watts with zero restriction.

You wouldn't want that kind of cfm because it would put the attic deep into negative pressure, increase leakage into

Ignore the ratings and marketing hype.

If your area gets decent wind you could probably get away with a turbine vent, get similar results.

 

[Gary in WA]

Solar fans only work when the sun is out..., pp.6;http://www.floridabuilding.org/FBC/publications/AtticVentReportFinal.pdf

Pay-back time; http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/

Turbines stop spinning when there is no wind- when you need it most.

Gary

 

[user_12345a]

Attic ventilation is over-rated. I would worry about just getting enough vents rather than looking at power venters.

 

[Splais]

thanks for links. very good articles.

 

[Bret86844]

it's a Natural Light SAF-24 Watt Solar Attic Fan, 1340cfm in up to 2100sf attic. No it is not a whole house fan.

Yeah, I wouldn't worry about moving too much air with that fan. And if you live in the Sahara Desert and are getting so much sun that it moves too much air, just partially block the inlet. It's not like efficiency matters when the power is free.