What's the verdict on attic fans?

[redpoint5]

I counted 21 square vents on my roof that have a rating of 38 sq/in of net free area for a total of 800 sq/in of attic exhaust capacity.

I then counted the number of 2" soffit vents that are rated 0.8 sq/in of net free area for a total of 58 sq/in of intake capacity.





The morons that "engineered" the roof put less than 1/10th the adequate intake capacity. This is roof construction 101 type knowledge; like a mathematician knowing how to add as part of their role as a math expert.

I'm thinking to get 15"x5" rectangular vents with a net free area of 42 sq/in (a single one providing nearly the same capacity as 72 of the existing vents). 19 of these will match the exhaust capacity.

[freebeard]

Beyond the intake/outflow there is the internal structure. I assume rafters or trusses on 16" centers, dividing the roof plane into cells.

You might do better with small vents on 16" centers.

[redpoint5]

Some might think that building codes could have been different ~20 years ago when the house was built, but the principles of fluid flow didn't change. Matching intake capacity with exhaust is a no-brainer.

The vacuum that develops as hot air escapes through the roof vents has to be replaced, and if it's not getting cool air from the soffits, then it's pulling inside air from from every poorly foamed hole that extends through the ceiling. In the summer it's trying to extract the AC cooled air into the attic to backfill the vacuum that is created by insufficient soffit flow.

Originally Posted by freebeard

Beyond the intake/outflow there is the internal structure. I assume rafters or trusses on 16" centers, dividing the roof plane into cells.

You might do better with small vents on 16" centers.

The 15" vents are 16" on center.