I brew in Fairbanks, Alaska, lots of cold weather brewing up here. Winter is my biggest brewing season because in the summer there is so much other stuff to do it can be hard to find time to brew. I boil and heat water outside. I do an infusion mash in a cooler. I usually carry the hot water inside and mash inside. I sparge indoors and carry my wort back outside to boil. After boil I bring the whole batch back in for chilling (37 degree well water
). I have no problem keeping my boil going at 20 or 25 below temperatures although I do blow through a lot more propane. The only time I've run into issues with my propane was this winter when I was doing a Barleywine and was doing a 2 hour boil. The propane tank started to freeze up and I had to swap it out for the one on the grill.
I've got the stainless to start doing 10 or 15 gallon batches but the way I have to carry all those hot liquids around 5 gallon batches are my limit. I think I'm going to get my large system running for summer brewing. I have some ideas for enclosing my brew space and getting a portable heater so I can do those large batches outside during the winter but haven't followed through on them yet.....