The rate of heat loss through a unit surface area of a window per unit temperature difference between the indoors and the outdoors is called the U-factor. The value of the U-factor ranges from about 1.25 W/m² · K (or 0.22 Btu/h · ft² · °F) for low-e coated, argon-filled, quadruple-pane windows to 6.25 W/m² · K (or 1.1 Btu/h · ft² · °F) for a single-pane window with aluminum frames. Determine the range for the rate of heat loss through a 1.2-m × 1.8-m window of a house that is maintained at 20°C when the outdoor air temperature is 28°C.

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Indoors 20°C 1.8 m 1.2 m, Outdoors -8°C O