I bought a 1k mag ballast to replace two 400's that were getting old. Heat, heat, heat....now I am upgrading my 4 inch to 6 inch fan because of the heat it puts out. If I grew just for myself, I would get the 600. Less problems with heat. HTG has satisfied me on every order. I am running their brand of inline fans....and I like them very much and they are reasonable. One think I will do for the summer will be lights out during the hottest part of they day.