I bought a 400w light because I wanted as much light as possible but it burned my plants. I raised it up the highest it will go so I think they are ok now. I'm venilating the room with a fan. The walls are just thin cotton sheets with mylar on the inside and the back right area is completely open so I don't think air exchange is a problem. Should I have gone with a lower wattage? Better fan? The area is pretty tall and I cant grow anywhere taller. I'm really bummed so if anyone has suggestions that would be great.

no you just have to have a open door because mh run very hot and you will notice the difference, because my mh had my grow room in the 100`s so i bought a different kind of mh and it kept it in the 80`s and when you get a hps it will be way lower, like my room is at 75 degrees max with hps

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stranger... stranger, now thats a weapon

You need to have your light as close as you can get it to your plants - otherwise you are just wasting money!

Yeah! They produce heat! You have to deal with that! Some kind of an "air-cooled hood" will suck the heat right out of an HID, either a Cool-tube or a hood vented with ducting.