Attic fan direction in or out ?

eco dude · 06-04-12, 03:15 PM

I have attic with two attic fans, each at one end of the attic. The are mounted in front of a dormer vent and each is pointing so that the air blows out.

I'm wondering if I should redirect one of them so that it points into the attic?? This way it would pull in cooler air from outside, create more of a flow thru the attic, and exhaust out the other like it does now...thoughts?

NeilBlanchard · 06-04-12, 03:56 PM

If there is a way for the air to be be pulled up through the house, then I'd leave it like it is. Running the fans when the temps are high up in the attic will cool the attic and the house; especially if you run them during the night and open up windows in the basement or in the rooms you want to cool.

herlichka · 06-04-12, 05:43 PM

They are probably both blowing out to pull outside air up through the soffits. This would help keep the lower roof sheathing cooler, and avoid hot spots where air is not circulating properly. Your shingles should last longer.

eco dude · 06-04-12, 09:56 PM

Ok, so NB please read again, these are attic fans NOT a WHF (Whole House Fan)...so they are only in the attic to exhaust heat from the attic.

Yah, I was thinkn the soffits pull outside air as well, but you know how it is when you get a draft flowing, as opposed to just air being pulled slowly from anywhere thru the soffits.

Also, I don't have the best options for vents since these are dormer vents and not a nice big gable vent. And, when I go on the roof and feel the exhaust I don't "feel" a lot of "hot air" like I would expect...thoughts on helping the air out of the attic, thanks?

iamgeo · 06-04-12, 10:54 PM

From your explanation it seems the attic fans are pulling more air through the dormer vents then through the soffits. Thus, they are not pulling the hot air out of the attic space. Very poor placement of the fans.

eco dude · 06-04-12, 11:31 PM

But what are my options, all I have is dormer vents? I know they made a difference when I installed them, but what else can I do? My roof is concrete tiles, and I'm just trying to improve the exhaust.

Ok, so more about the house. It's a 2-story, my bedroom is directly above a the garage, which the mrs. likes to park in when "a million" degrees outside, then as the car sits in the garage, the heat radiates thru the garage ceiling and in thru the bedroom floor, meanwhile the attic heat is building up, so now it feels like a nice toasty "hot dog bun" when I'm trying to sleep at nite....argh!

Anyway, my dilemna with trying to dissipate the heat from various sources so the upstairs is not so hot.

NeilBlanchard · 06-05-12, 06:55 AM

I'd leave the fans as they are; as the heated air is going to "want" to exhaust out on its own even if the fans were not running. So, they are assisting the natural flow. If air is getting into the attic from anywhere it is better than nothing. Even within the attic, the air will be stratified by the heat.

What color are the roof tiles? Could they be painted white, to lower their albedo? This would cool the attic substantially.

You should consider replacing the fans with a whole house fan, if they are still not up to the task. Or at least add a few more smaller fans. I have two window fans in my attic installed in the only two small double hung windows up there, and even though they are far lower CFM than a whole house fan, they do a great deal to cool the whole house overnight; and thereby they help it a lot during the next day, as well.

iamgeo · 06-05-12, 08:50 AM

Another question is, Do you have enough soffit vents?
Have you thought of putting an exhaust fan in the garage?
Start a "project" in the garage that takes up too much room.

eco dude · 06-05-12, 10:21 AM

Oky-doky, I'll leave the fans as is, pointing out. Oh yea, tiles are brownish/greyish color and I live in an association, so I don't think I can paint them.

I'm also wondering how then to maybe get more air flow exhausting thru the the dormer vent. The dormer vent is ~18" across, but it's really only a semi-circle. The attic fan's are ~18" as well, but they're trying to push that air thru a smaller hole via the dormer vent. I'm going to really seal off the attic fan housing so that it's air-tight to the roof too.

So, I'm not really wanting to do an roof cutting or tile work, is there any way to make the dormer vent bigger to allow more air flow from the attic fan?

iamgeo · 06-05-12, 08:55 PM

Ohhhh, I totally misread your first post. Now I understand.
But the question still remains unanswered. Do you have enough soffit vents?
Have you ever put a box fan too close to a wall?

06-04-12, 03:15 PM	#1
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	Attic fan direction in or out ? I have attic with two attic fans, each at one end of the attic. The are mounted in front of a dormer vent and each is pointing so that the air blows out. I'm wondering if I should redirect one of them so that it points into the attic?? This way it would pull in cooler air from outside, create more of a flow thru the attic, and exhaust out the other like it does now...thoughts?

06-05-12, 10:21 AM	#9
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	Oky-doky, I'll leave the fans as is, pointing out. Oh yea, tiles are brownish/greyish color and I live in an association, so I don't think I can paint them. I'm also wondering how then to maybe get more air flow exhausting thru the the dormer vent. The dormer vent is ~18" across, but it's really only a semi-circle. The attic fan's are ~18" as well, but they're trying to push that air thru a smaller hole via the dormer vent. I'm going to really seal off the attic fan housing so that it's air-tight to the roof too. So, I'm not really wanting to do an roof cutting or tile work, is there any way to make the dormer vent bigger to allow more air flow from the attic fan? Last edited by eco dude; 06-05-12 at 11:05 AM..

06-04-12, 03:56 PM	#2
NeilBlanchard Journeyman EcoRenovator Join Date: Dec 2009 Location: Maynard, MA Eaarth Posts: 383 Thanks: 78 Thanked 39 Times in 32 Posts	If there is a way for the air to be be pulled up through the house, then I'd leave it like it is. Running the fans when the temps are high up in the attic will cool the attic and the house; especially if you run them during the night and open up windows in the basement or in the rooms you want to cool.

06-04-12, 05:43 PM	#3
herlichka Apprentice EcoRenovator Join Date: Oct 2010 Location: Simcoe County, Ontario, Canada Posts: 102 Thanks: 11 Thanked 15 Times in 10 Posts	They are probably both blowing out to pull outside air up through the soffits. This would help keep the lower roof sheathing cooler, and avoid hot spots where air is not circulating properly. Your shingles should last longer.

06-04-12, 09:56 PM	#4
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	Ok, so NB please read again, these are attic fans NOT a WHF (Whole House Fan)...so they are only in the attic to exhaust heat from the attic. Yah, I was thinkn the soffits pull outside air as well, but you know how it is when you get a draft flowing, as opposed to just air being pulled slowly from anywhere thru the soffits. Also, I don't have the best options for vents since these are dormer vents and not a nice big gable vent. And, when I go on the roof and feel the exhaust I don't "feel" a lot of "hot air" like I would expect...thoughts on helping the air out of the attic, thanks?

06-04-12, 10:54 PM	#5
iamgeo Apprentice EcoRenovator Join Date: Aug 2010 Location: Lakehills, Tx Posts: 168 Thanks: 4 Thanked 10 Times in 9 Posts	From your explanation it seems the attic fans are pulling more air through the dormer vents then through the soffits. Thus, they are not pulling the hot air out of the attic space. Very poor placement of the fans.

06-04-12, 11:31 PM	#6
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	But what are my options, all I have is dormer vents? I know they made a difference when I installed them, but what else can I do? My roof is concrete tiles, and I'm just trying to improve the exhaust. Ok, so more about the house. It's a 2-story, my bedroom is directly above a the garage, which the mrs. likes to park in when "a million" degrees outside, then as the car sits in the garage, the heat radiates thru the garage ceiling and in thru the bedroom floor, meanwhile the attic heat is building up, so now it feels like a nice toasty "hot dog bun" when I'm trying to sleep at nite....argh! Anyway, my dilemna with trying to dissipate the heat from various sources so the upstairs is not so hot.

06-05-12, 06:55 AM	#7
NeilBlanchard Journeyman EcoRenovator Join Date: Dec 2009 Location: Maynard, MA Eaarth Posts: 383 Thanks: 78 Thanked 39 Times in 32 Posts	I'd leave the fans as they are; as the heated air is going to "want" to exhaust out on its own even if the fans were not running. So, they are assisting the natural flow. If air is getting into the attic from anywhere it is better than nothing. Even within the attic, the air will be stratified by the heat. What color are the roof tiles? Could they be painted white, to lower their albedo? This would cool the attic substantially. You should consider replacing the fans with a whole house fan, if they are still not up to the task. Or at least add a few more smaller fans. I have two window fans in my attic installed in the only two small double hung windows up there, and even though they are far lower CFM than a whole house fan, they do a great deal to cool the whole house overnight; and thereby they help it a lot during the next day, as well.

06-05-12, 08:50 AM	#8
iamgeo Apprentice EcoRenovator Join Date: Aug 2010 Location: Lakehills, Tx Posts: 168 Thanks: 4 Thanked 10 Times in 9 Posts	Another question is, Do you have enough soffit vents? Have you thought of putting an exhaust fan in the garage? Start a "project" in the garage that takes up too much room.

06-05-12, 08:55 PM	#10
iamgeo Apprentice EcoRenovator Join Date: Aug 2010 Location: Lakehills, Tx Posts: 168 Thanks: 4 Thanked 10 Times in 9 Posts	Ohhhh, I totally misread your first post. Now I understand. But the question still remains unanswered. Do you have enough soffit vents? Have you ever put a box fan too close to a wall?