1 A window installer should remove the existing windows, install the new ones, cleanup and dispose of the old windows, and wash the new windows. 2  Estimates are usually based on united inches, which is equal to the sum of the length and width of each window; a 40x55-inch window is 95 united inches.dditional costs: 1  A window installer should remove the existing windows, install the new ones, cleanup and dispose of the old windows, and wash the new windows. 2  Estimates are usually based on united inches, which is equal to the sum of the length and width of each window; a 40x55-inch window is 95 united inches.