I have a customer that did a "do-it-yourself-project" and put a small addition onto their home. They cut the end of the duct and extended it into this space. The problem is that the air isn't making it their. The original install didn't include any dampers so I can't balance it properly and am trying to find a quick and easy solution here. I have never used inline booster fans and would like everyones opinion of them. The duct where they would be installed is 10"x8" so what I was thinking was to install two 4" round inline fans. Your comments are appreciated.