How much does a 400w raise the temperature? Assume you have adequate ventilation but the hood isn't hooked up to a fan. Also how many LST'd plants do you figure could be flowered in a 20"x36" area?
For the tempature question, its to hard to predict your actual temp your gonna have with a 400, but expect it to raise the room temp by 15-20 degrees before some kind of air movement.