The thing you will have to be carefull of with red hot windows, is thermal shock!
Ok in the summer when outside Temperatures are high, but come the winter, when you put cold water on the outside, and its red hot inside, you could crack the glass,
my advice would be to use warm/hot water, at least the risk of Thermal shock would be lower
Scrimit2 give's good advice, try to get there early in the morning.