I avoid hot water at the risk of breaking the glass. Luke warm or even cold water on the other hand can be safely used without the risk of breaking glass. What you have to remember is that liquid water, at any temperature is hotter than ice and will therefore melt it. Also for use in locks steaming hot water will actually get into the lock and refreeze very quickly and sometimes violently, cold will not. I've seen door locks completely destroyed by steaming hot water, the slightly lucky end up with their keys stuck in the lock, sometimes permanently. I have personally wound up with a door that refroze with the latch open, preventing me from closing my door. Again, that's using STEAMING hot water, no ill effects so far using cold water.
