I was whimsically alluding to Cornwall's mild climate, in which you only occasionally need to resort to de-icing the screen. We've had six frosty mornings so far this winter with nothing below -2.5C. That definitely allows you to get a big watering can of hot tap water to defrost the screen. No screen will be harmed, and, unlike other methods, it will help to unfog the inside of the screen too.