For me the answer is always yes if there is any question. I have had frozen lines once and I am sure that drives my decisions. Not a fun time. Im sure that it will get cooler no matter where you live and as was mentioned it has more to do with how long rather then how cold. I am set up so I can winterize in about 5 minutes. Then when I dewinterize I save the antifreeze from the lines to use in the drains next time. By doing that I can winterize with only 1 gal of antifreeze. For me that is not worth the chance that it may freeze up.
