I mostly use partial mash to brew. I may do things a little different, but I brew on a stove. Therefore, I cannot do a full boil. I can do 3-4 gallon boil. When done, I use a cold water bath to get my temp down to around 100-120F. Then I use a two liter bottle of water that has been sanitized and froze prior to brew day. I cut that bottle up with a sanitized knife and put it in my wort and it takes it down that final 30 degrees or so. Works like a charm and I have not had any problems yet.