I am purchasing a mid century home in AZ which has numerous sliders and glass (one whole side of the house). The house is 4000 sq. ft. with a 7000 sq. foot roof. The roof includes a portion that extends 6-8 linear ft. over the side of the house that has the wall of glass. The glass is the original single pane from the 50's. I cannot access a previous electric bill as the house has been unoccupied. I am wondering what I am in for with electric bill and how cost effective it will be to replace the glass (I am guessing 30-50k?). Today, with temps. approaching 100, the inside was nice and cool (no electricity turned on yet), but the worst is yet to come (still cooling off at night). Thank you.