I have similiar problems right now. I am only running a 400w MH, but it is putting off about as much heat as I'd want to have to deal with. I have been trying to find a fan that is quiet enough for me to use in my apartment without fear of a neighbor hearing it (I have a tent in my closet). I put a blower in there and it was way too loud so I went and got an inline 4" fan the other day. It is way to loud too. I just ordered a speed controller for it today so hopefully I can turn it down to the point where it is quiet enough. I just hope it still moves enough air. Without good ventilation in that tent I'll cook my plants with that 400w MH. I had to pull that light out and put my 150w HPS in there for now so I don't over heat the tent until I get my speed controller in and can reinstall my fan. Luckily my plants are only a couple weeks old so that light is more than enough to cover them right now.