Thanks FenEx. I did mean to define U value and not LowE. Dislexia I guess. The guestimate calculation works well in my area and may not work well in yours. The basic laymans theory behind U values windows and energy costs was explored. Products in my area with a good U value traditionally have an acceptable SHGC. I am also understanding from literature that the farther north you go the less importance of SHGC comes into play with more emphasis to U values.
Can we get a FenEx checker on this board(its like a spell checker
50 year old units would be either wood, aluminum or steel with single pane glass. You should see a significant savings replacing the wood and a mondo-dramatic savings if you have steel or aluminum. The U value of 0.18 is very good, actually its rare. In addition to energy savings there is one thing you can't put a real dollar value, comfort. Your home should much more comfortable.