I am buying a small fan for a small carbon filter and was wondering if I can use it later to added to the CFM I get from another filter/fan (when i move my grow to a bigger room down the line)?
Not necessarily. It depends on how you have them set up. If each has its own exhaust hole then in most circumstances the answer is yes, but if you are trying to push more and more air out of the same one exhaust hole then the size of the hole can limit the effectiveness of the fans. Also depends how you have the fans set up.