well currently we have a 128cfm rat wheel style fan that is air cooling our 400w HPS light. The light stays ultra cool as you could imagine. My issue of course is yield. Not this time, and maybe not even the next grow but in the future we are going to want another 400w or maybe a 600w to replace this one. Katacus touched on the fact that he was running two 400w lights and it was working out fine, but that's all the info he blessed us with!

The main point of my thread is to see about running two 400w lights. We would have to get a stronger centrifugal fan probably but that is no big deal when it comes to yield. BTW we DO have a narrow small grow room. It is probably about 8ft x 4.5ft and about 7.5ft tall at the tallest point. Thanks for the help guys!