For many homes, installation of a pre-manufactured WHF is quite simple. Calculate the volume of your home (square feet of floor space times average ceiling height) and use readily available formulas to determine the size of the fan you need. Then cut a properly reinforced hole in your ceiling based upon the size of the fan you are using and mount the unit. You also need to calculate and allow for the proper amount of roof venting. There are many pre-manufactured WHF units which can be found at big box stores and on the internet.
In our case, however, we ran into two snags during the planning phases of the project. While our home has a relatively modest 2,383 square feet of floor space, our ceilings are 10 feet tall rather than the normal eight. As a result, the volume of air we needed to move was larger than most typical homes and beyond the capacity of most lower cost WHFs.
Our second, and larger, problem was that whole house fans are designed to operate in a horizontal position. Unfortunately, due to truss design and a maze of duct work, there was virtually no area in our attic where a “store bought” WHF could be mounted horizontally.
As a result, we ended up designing and building our own vertical WHF. We used a “drum fan” which is made to operate an a vertical position and has the additional benefit of moving large amounts or air at a lower cost than typical whole house fans.