rework example $4\mathrm{.}2,$ now assuming that the house has $14$ windows, each measuring $45$ inches high by $32$ inches wide. When you buy the house, they$$re single$-$ pane windows, but when you upgrade the insulation, you also upgrade the windows to the best you can buy $($see table $4\mathrm{.}2).$ remember that the windows replace some of the wall area. Neglect any solar gain through the windows, which would increase your savings even more.