One very important aspect when installing a whole house fan is the amount of venting available in the attic. We recommend having 1 square foot of net free venting, for every 750 CFM in the QuietCool system.
For example, if a customer installs a QuietCool Trident Pro 4.8, they are pulling in roughly 4,740 CFM. If you divide that by 750, you get the number, 6.32. This is telling you that you would need 6.32 square feet of net free venting to properly ventilate all the air you are pulling in.
To simplify this, you can only bring in as much as you can take out. This is important because air, like water takes the path of least resistance. The air must go somewhere, and if there is not enough venting, the air will go back down the walls.
Calculating the venting in your attic
So now that we have explained the importance of proper venting, let’s explain how to calculate the amount of venting you have. The process is simple:
First, measure the length and width of every vent in the attic (every vent counts: gables, soffits, ridge vents, whirly birds, even bird holes).
Next, divide the total number you came up with by 144 (this converts the amount of venting into square feet).
Finally, multiply the number of square feet you have by 0.75 (this considers the screening on each vent to keep insects out).
This last number is the amount of Net Free Vent Area (NFVA) your attic has.
Now that you are experts in venting go ahead and purchase your very own QuietCool whole house fan!