Luke warm does a great job. The hose behaves likes it's summer, the whole experience is pleasanter, easier on your part and requires less effort.
How edd (vedd) cracks glass I don't know. My heat loss through the hose is massive. That's the problem I'm currently working on.
Mr solubility, try this test, get a glass and put it in the freezer, boil kettle and pour some water in bowl, take glass out of freezer when very cold and place in very hot water, lot of the time this glass will break. and at this time of year glass is very cold
Last year I left a pole resting against a bedroom window sill and drove home. Customer phoned to say my brush was where I left it, so I arranged to collect it the following morning. When I got there my pole had actually frozen to the window sill and I had to get a ladder and a kettle of hot water just to remove it from the window sill. Took a good hour thawing in the sun before I could use it again.
Hot water on glass can crack glass because of the thermo shock.
When cold WFP users are waiting for the day to warm up because they can't get the water to go through the hose that goes up through their WFpoles (because it has frozen), the hot WFP users can continue to work using tepid to warm water without the hassles.