I was working a retirement breakfast today at a ac repair place and asked the owner if they had any laying around. He just gave me this for free. I know absolutely nothing about it except that it is four speed. I have been planning to build a flow hood for a bit. And if this one will work then I'm going to start building. I have been reading flow food builds and I'm not sure were to find out about speeds and the mathematics on finding the correct size filter. Any info on this particular blower would be great.