Please forgive my ignorance on this. A new window just arrived that I ordered to replace a damaged one in my new house. It has a green film on it which I understand is energy saving; it blocks heat from going in or out. What happened to passive solar? This is a south facing window. It never gets too hot so I'm not worried about too much heat getting in in the summer. Even though it will keep in the furnace heat in the winter won't I be missing out on a lot of heat from the source itself???