On a cold water system how cold can it be and still work? Looking at -4 here all day. Thinking my hose will freeze at that temp 
ive worked in -2 before now with a cold system but it was hard going.my jets freezed up a couple of times.take some hot water in a flask to thaw them out if they do freeze.you can also get ice building up on your pole near the clamps.your hose will freeze on frozen ground if you dont keep the water running through it too.also some windows without heating will freeze up almost instantly.