posted by Sierra .
Use the exact values you enter in previous answer(s) to make later calculation(s).
Energy-efficient windows are constructed with two panes of glass separated by an air gap (see figure below). In a typical window of this type, the air gap makes a huge difference in the rate of heat flow. The heat-flow rate is much smaller for an energy-efficient window than for a single pane of glass because the thermal conductivity of the air gap is much less than that of a glass pane.