Remember your trying to temp the metal. So if you can keep the temps at about 225 max. If you go over, either cool it with a house fan or shut it down and let it cool down and restart. Do not run both tanks without a shutdown. You need to let the metal temper and heating and cooling is the best way to accomplish this task. Best practice is to run 1/2 tank shutdown and do this four times. Tempering the metal is the key here.