A word of advice. If you get frost or ice on your windshield, don't pour boiling water on it to melt it off. (people actually do that, really not a very good idea).
My Dad taught me to fill 2 hot water bottles with near boiling water, nip out and put them on the dashboard top. Then get ready for work, shower breakfast etc.
By the time you are ready to drive the heat has melted most of the ice. You press the hot water bottle onto the windscreen and hold it for a few seconds on any area not melted. Then put the bottle on your knee and have a warm knee as you drive.