Help with attic fan efficiency
I'm trying to determine if my attic has enough vent openings to efficiently run an already installed attic fan. The fan I have is the following.
Looking at the specs, it appears on high speed the fan is capable of exhausting 8480 cfm?
Now, upon my research, I've found it's recommended to have 1 square foot of attic vent opening per 1,000 cfm fan capacity. And if your vents have screens on them, you need more like 2 square feet of vent opening per 1,000 cfm fan capacity.
So, in my attic, I have two louvered and screened square vents on each end measuring 14.5"x10.75". There's two screened circular vents in the roof with 9" diameters. And that's it. No gable vent or soffit vents.
According to my calculations, I should have close to 17 square feet of screened vents for an 8480 cfm fan, however, in reality, I only have almost 3 square feet.
Am I on the right track here with figuring this out? Would the builder not put in enough attic vents? The house was built in '76 and I'm pretty sure the fan is original with the house.
I started checking into this when I heard a radio handyman talk host mention it should only take 10-15 minutes of running your attic fan to cool the house. For my house, I can run the fan for a couple of hours and still not get the house cooled.
Can anyone help me figure this out?