Consider an ordinary house with R-13 walls (walls that have an R-value of 13 h · ft² · °F/Btu). Compare this to the R-value of the common double-door windows that are double pane with 14 in of air space and have aluminum frames. If the windows occupy only 20 percent of the wall area, determine if more heat is lost through the windows or through the remaining 80 percent of the wall area. Disregard infiltration losses.