Check out my grow log under indoor growing. I'm using a 600w hps with an air cooled hood and a 6in inline HD fan, its in the closet with the doors removed making the grow room about 10x12. Temps stay at 75-85 deg throughout the day and i'll sometimes open the window a bit to lower temps its 50-60deg outside so that definitely helps I'm sure i'll need real ventilation in the summer but everything is good so far using the 600w and venting back into the grow room. I also keep the door to the room open so the house regulates the temp some.