Attic ventilation question

[pauls340]

I have 9 or10 roof box vents on the backside of the house (1240 sqft), we have a gable fan at one end and is set at 100 degrees. It does a very poor job removing the hot air in the attic. I was told the roof vents are useless since the fan only ***** air from the first two or three vents closes to the fan. He told me to cut 12" square pieces of plywood and cover those vent holes up so the gable fan pulls air thru the attic...it makes sense, what say you?

 

[36tbird]

I have a solar powered gable fan and I think it is set to not run below 62 degrees. I don't understand why your fan's thermostat is set so high. Seems like waiting for it to come on at 100 leaves it playing catch up to move that hot air out.

 

[Jeffksf]

Do you have soffit vents? I was told that if you have good soffit vents and good ridge vent then no fans are really needed
You get a draft setup that pulls air thru the attic from low to high then.

 

[georgelowcar]

I have been looking at ridge vents, as i was questioning how well mine was working. It looks like ridge vents/soft vents don't do as well unless you have a little wind (Bernoulli effect). Also, the orientation of the ridge vent/soft vents with the wind can is described as making a big difference.

 

[gordon_gjs]

I have 9 or10 roof box vents on the backside of the house (1240 sqft), we have a gable fan at one end and is set at 100 degrees. It does a very poor job removing the hot air in the attic. I was told the roof vents are useless since the fan only ***** air from the first two or three vents closes to the fan. He told me to cut 12" square pieces of plywood and cover those vent holes up so the gable fan pulls air thru the attic...it makes sense, what say you?

That is correct. If the fan is not pulling air from the soffits then it is not doing its job. Cool air needs to be pull thru the soffits to replace the hot air expelled thru the fan.

I have a solar powered gable fan and I think it is set to not run below 62 degrees. I don't understand why your fan's thermostat is set so high. Seems like waiting for it to come on at 100 leaves it playing catch up to move that hot air out.

62 degrees is to low. The fan would never shut off. I have mine set to 95 degress right now and I live in Houston, Tx.
Mine is also not solar powered, so running it 24/7 would not be energy efficient. You have to remember that the purpose of the fan is to expell hot air from the attic and 62 degress is not hot air.

But in you're case I suppose running a solar powered at 62 degrees wouldnt hurt anything other then shorten the motor life.

 

[36tbird]

You're right, 62 is too low. I don't remember what it is. But, isn't 100 too high?

 

[zoomzoomjeff]

Powered attic ventialtors are useless.

Your attic is cooler because the cool air from your home is being sucked out... and warm, humid air is being sucked in... to then be cooled, and sucked out through the attic.

Performance of fiberglass diminishes rapidly as air moves through it. Powered attic ventialtors move air through fiberglass.

Turn it off.

You must be talking about whole house exhaust fans??? And you must be assuming he is running the fan WITH the A/C on. Otherwise, none of what you wrote makes any sense.

 

[zoomzoomjeff]

I have 9 or10 roof box vents on the backside of the house (1240 sqft), we have a gable fan at one end and is set at 100 degrees. It does a very poor job removing the hot air in the attic. I was told the roof vents are useless since the fan only ***** air from the first two or three vents closes to the fan. He told me to cut 12" square pieces of plywood and cover those vent holes up so the gable fan pulls air thru the attic...it makes sense, what say you?

I've been researching ventilation methods for my 1 1/2 story house and from what I've been reading lately, that actually makes sense. The professional HVAC guys and air handling gurus say you use one of two things:
a) either use soffit vents with roof vents(or a ridge vent) or
b) gable vents. But not both.

There are more detailed inputs into your equation like do you have a ridge vent? what type of insulation? are the soffits blocked by insulation? are the roof vents at least 3-5 feet up from the soffits? how many gable vents? etc. I'm not the licensed expert, but just passing on what I've read in the past 15 hours of net searching. The only other suggestion I might have is you could block the gable vents and see if the natural stack effect works with your existing soffits/roof vent system. If not, block the roof vents and turn the gable fan back on. It should cool more effectively.

 

[Jay41]

Powered attic ventialtors are useless.

Your attic is cooler because the cool air from your home is being sucked out... and warm, humid air is being sucked in... to then be cooled, and sucked out through the attic.

Performance of fiberglass diminishes rapidly as air moves through it. Powered attic ventialtors move air through fiberglass.

Turn it off.

Agree.
pavs cause other problems as well.

 

[Jay41]

You must be talking about whole house exhaust fans??? And you must be assuming he is running the fan WITH the A/C on. Otherwise, none of what you wrote makes any sense.

Someone has never been to air balancing class.

 

[zoomzoomjeff]

To danski0224--
THAT post made sense to me--thank you for posting all of the info. I apologize for my quick judgement--it was made without knowing the facts you posted on followup. That is precisely the kind of information I'm looking for. (and it looks like you're apparently one of the "air handling gurus" I referred to earlier)

I was very close to pulling the trigger on buying and installing a gable vent fan for my cape code home, with our master bedroom upstairs. When it's 90* outside, the AC will cool the house to 74*, and upstairs will be 84*. It's also colder in the winter up there. We had reflective foil installed in the attic this winter. That reduced the temp difference by 3* during the winter, but only about 1* during the summer. I knew it wouldn't be the cure-all, but the idealist in me was hoping for more.

Everything I've read says those gable fans are about the only cost-effective solution for cape cods, short of different roof construction. House was bought 2 years ago, with a new roof, no soffits, no roof vents, no ridge cap. Just 6 East/West gable vents--2 on each side attic, and 2 on the top peak. I'm back to square one after reading your post. Suggestions?

Agree.
pavs cause other problems as well.

Can you elaborate?

Someone has never been to air balancing class.

Clearly. See humble post above.

 

[zoomzoomjeff]

Closed cell or open cell?

Any accreditations I should look for when calling on people? Instead of looking for "contractor" in the yellow pages, should I be searching for something more specific?

Thanks.

 

[csp]

Look under insulation.

 

[brownsl]

Redefine your thermal boundary.

Spray foam the roof.

No ventilation needed.

I am looking at getting my detached, garage insulated. I was leaning towards spray foaming the ceiling and leave the soffit and gable vents open. Someone mentioned to me that I could instead spray the roof and gable ends and I could spray close the soffit and ridge vents. Is this a good idea?

 

[Frank The Plumber]

Be careful with these whole house fans and attic fans. You can get the house to a negative pressure and lock out your water heater and or other appliances, or pull your CO from the heater into the home.

 

[brownsl]

Close off the ventilation openings and spray the roof and gable ends.

Pay attention to the soffits.

The "attic" is now conditioned space.

I am unclear on what you mean by "Pay attention to the soffits." Do you mean to make sure that they are closed off by the foam.

Do I need to worry about lack of ventilation in the garage?

What is the benefit to spraying the roof/gable over spraying just the ceiling?

Thanks for the advice.

 

[R6 Racer]

I'll start out with a "I'm sorry" cause I didn't read the whole thread & I might be repeating someone. BUT... My dad also had a problem with his attic heating up. He tried a bunch of stuff that kinda worked. In the end he put a greenhouse fan (he tried smaller fans but they didn't do the job) in the ceiling of his garage, with the fan pushing air into the attic. Solved all his problems. The fan was powerful enough (that was the key) to force air out all the vents. It took about 2 minutes to completely cool down the whole attic. He could drop the temperature up there down by 20 to 30 degrees in a very short time.

Steve

 

[Rosco]

I installed the hardiboard soffits all the way around my house and detached garage. They have a series of holes that run the entire length, so air gets in from all directions. My garage has the hardiboard soffits, gable vent on each end and off-ridge vents on the dormers. Due to the black shingles and bonus room I added a powered exhaust fan to the north end gable. When turned on it pulls the hot air right out from the other gable end. The dormer vents are there just for static heat exhaust, as the dormer roof is only 8' X 8' hip. Most of the issues seen in the south (unless foam insulation is used) is not enough soffit vents.

 

[leslikj]

Every homeowner in the country faces the same problems with clogged soffit vents.
This affects the entire attic's ventilation systems efficiency. There is a brand new product that solves this problem. It is the only one-time replacement soffit vent that is serviceable and cleanable. It has a removable, cleanable, and reusable filter insert and it comes with a lifetime warranty. Check it out at www.superiorsoffit.com

 

[Tymscholl]

I have soffits and ridge vents but my attic is still way too hot.

 

[Tymscholl]

Ridge vents don't keep the rain out during a hurricane though here in Florida.

 

[rackeu]

I am thinking of using a small whole house fan to keep my garage cool while working in it. I am not using it much and don’t need full time cooling. The garage is attached on one wall to the house, completely sheet rocked and the ceiling and walls have no insulation. I understand that insulation would go a very long way but I think it would help just pulling the hot air out of the top of the garage. The attic area over the garage does not have a ridge vent, gables or any other vent other than full soffit vents around 3 sides. With that design I wouldn’t think there is any passive air exchange and I have a hot attic radiating heat down into the garage. There is nothing in the attic and nothing that would generate CO2 in the garage.

My thinking is that a small whole house fan would pull hot air out of the top of the garage which would also displace the hot air already in the attic space expelling the air out through the soffit vents. In this manner I could get at least ambient outside temperature (with a breeze) when working in the garage. I guess it would also be possible to "steal" a little AC from the house if I left the door to the house open when I need something extra to take the edge off.

Can you see anything wrong with my logic? Is this worth giving it a try?