The base case heating and cooling costs are calculated for the house with single pane glass in aluminum frame windows - this is represented by the 100% cost figure.

Each different window case is shown with a heating and cooling utility bill represented by the percentage of the base 100% case. Remember, this is not your entire gas and electric bill; it just includes the portion spend for heating and cooling the home.

The results show that changing from single pane to double pane standard glass in an aluminum frame might save 10%, using low solar low-E glass in aluminum frames might save 25%, and choosing low solar low E glass in a wood or vinyl frame could save over 30% on the annual heating/cooling costs.

Given the relatively low cost of upgrading to low solar heat gain low-E glass (usually less than $2 per square foot of window area), the payback time for the incremental cost of high performance glass will be short.