I actually do a lot of work with fans and am about to get one of the AC Cloudlines or an Iobonics in line. These have an EC motor, which is basically a DC motor - super efficient and can be turned down to 0. standard variable speed AC fans only drop to around 60% of max flow. I agree with oversizing with these ones because of the super turndown with no loss in efficiency. I do caution you if comparing flow rates of different fans/ to check the static, which is the pressure it can push. In my looking for this fan, I was surprised to find many of them were rated at atmospheric, or some other obscure wording that means it's flow was measured with no resistance. then you get it home and add ducting and the filter , which could super reduce the airflow. The AC cloudline and the iobonics are rated for their flows at a fairly high static - a very reputable way of doing it. Iobonics has a deal on for a filter , ductwork, and filter in all sizes. I wil be getting a 6 inch, even though a 4 inch will do it, in case of the future and for noise. Cheers.