i wonder if you switched from a 400watt magnetic ballast to a 600 digital the percentage of heat would change
still good info
I think having he ballast itself in the growroom would change his formula.. Looks like it only factored bulb heat. Not heat emmitted by the ballast. Having the ballast outside the growroom makes a big difference in room temps. If you have no problems at all keeping things cool now, then you should be able to handle the upgrade. Worse case you would have to get a larger exhaust fan and maybe circulate a bit more air in the room.
