Call me a puff if you like but anything under -1 then I dont bother.

So long as they have heating on then the glass will be warm.
Keep the water flowing when hose on ground and it prob wont freeze even if you just have a trickle running thru it
When we had -15 the year before last I tried trad with deicer in my bucket but it still froze a luvly shade of blue
