Attic fan direction in or out ? - Page 2

eco dude · 06-05-12, 11:42 PM

ahhhh, ya, I know what you mean by a box fan too close to the wall, but how does that relate to this? and, how do I test or how do I know if I have enuf soffit vents?

iamgeo · 06-06-12, 11:26 PM

There is some math that you have to do......I will look for the pages.
When the fan is too close to the wall it can not pull a lot of air through it. As you get it farther from the wall you will notice it can move more air. Well, think of not having enough soffit vents like the fan being too close to the wall.

eco dude · 06-07-12, 12:11 AM

the attic fan is mounted near the top of the roof truss so I think it's got plenty of room "behind" it and between the soffit vents to grab air...um, I think that should be enuf??

I got no way to measure the air movement to make sure. Any ideas to help me see the airflow? I'm thinking something like a cig lighter and holding the flame kinda close to see if it's "bending" with the airflow.

iamgeo · 06-07-12, 08:29 PM

When the fans are on they are pushing air out of the attic. If there is not enough soffit vent area the amount of air entering the attic will be limited. Also, the nice cool air in the house can be pulled out and into the attic, thus causing your A/C to run more.

eco dude · 06-08-12, 10:32 AM

Again, how do I determine if I have enuf soffit vent area? Also, how do you mean cool air can be pulled out and into the attic?

S-F · 06-09-12, 12:33 AM

Make sure you have continuous soffit vents, air seal the attic and blow R 60, stay cool and never look back?

Having a hot attic is fine as long as you have enough insulation up there. The ventilation in attics is to control moisture, not heat. The BSC posted an article about this a week or so ago.

BSI-060: Joe South Assemblies — Building Science Information

eco dude · 06-10-12, 04:06 PM

Got it, great article...thanks, and will be stay'n cooler now!

06-05-12, 11:42 PM	#11
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	ahhhh, ya, I know what you mean by a box fan too close to the wall, but how does that relate to this? and, how do I test or how do I know if I have enuf soffit vents?

06-06-12, 11:26 PM	#12
iamgeo Apprentice EcoRenovator Join Date: Aug 2010 Location: Lakehills, Tx Posts: 168 Thanks: 4 Thanked 10 Times in 9 Posts	There is some math that you have to do......I will look for the pages. When the fan is too close to the wall it can not pull a lot of air through it. As you get it farther from the wall you will notice it can move more air. Well, think of not having enough soffit vents like the fan being too close to the wall.

06-07-12, 12:11 AM	#13
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	the attic fan is mounted near the top of the roof truss so I think it's got plenty of room "behind" it and between the soffit vents to grab air...um, I think that should be enuf?? I got no way to measure the air movement to make sure. Any ideas to help me see the airflow? I'm thinking something like a cig lighter and holding the flame kinda close to see if it's "bending" with the airflow.

06-07-12, 08:29 PM	#14
iamgeo Apprentice EcoRenovator Join Date: Aug 2010 Location: Lakehills, Tx Posts: 168 Thanks: 4 Thanked 10 Times in 9 Posts	When the fans are on they are pushing air out of the attic. If there is not enough soffit vent area the amount of air entering the attic will be limited. Also, the nice cool air in the house can be pulled out and into the attic, thus causing your A/C to run more.

06-08-12, 10:32 AM	#15
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	Again, how do I determine if I have enuf soffit vent area? Also, how do you mean cool air can be pulled out and into the attic?

06-10-12, 04:06 PM	#17
eco dude Helper EcoRenovator Join Date: Mar 2011 Location: Sacramento Posts: 32 Thanks: 0 Thanked 0 Times in 0 Posts	Got it, great article...thanks, and will be stay'n cooler now!