I am designing a retirement home in Bucks County, PA. It will have an integrated 10 x 20 Sunroom for Passive Solar Heating. I am looking for a window with a low U value combined with a high (.6 or higher) solar heat gain coefficient. To date I have not been able to find a American made windows, only one type made in Europe (Fenestra) , price at over $100/SF. Any suggestions would be appreciated.....Thanks, Bob