Heat Loss of a Single Paned Window System

Heat Loss

• Heat loss is the transfer of heat energy from an object, such as a house, to the local environment. The heat passes through the materials that make up the exterior of the house during its transfer, slowed down at different rates depending on the material at a given point. The degree to which a given material, such as a single-pane window, conducts heat is known as its U-value: A single pane of glass has a U-value of 1.1.

Impact of Temperature Difference

• The difference between internal and external temperatures has a significant effect on the loss of heat. Even if your windows are wide open, you won't lose any heat if it's just as warm outside as it is in your house. If you are experiencing very cold weather, however, the loss of heat through a single-pane window is compounded several times. In warm climates, the heat retention of construction materials is much less important.

Calculating the Loss

• You can calculate the heat loss of any given material by multiplying its U-value by its area in square feet by the internal-to-external temperature difference. If your house has 80 square feet of single-pane windows, you keep your home at 60 degrees Fahrenheit and it's 40 degrees outside, this equation would be 1.1 --- 80 --- 20 = 1,760 BTUs of heat lost through the windows every hour. Adjust the area and temperature values as necessary to calculate the heat loss of your windows.

Reducing Window Heat Loss

• Double- or triple-paned windows can drastically cut down on the loss of heat, with greater spaces between them providing better insulation. The U-value of two panes set 1/4 inch apart is 0.6, while a 1/2-inch space reduces that to 0.5. A triple-pane window with 1/4 inch of space has a 0.4 U-value, and 1/2 inch between each pane reduces that to 0.3. Replacing the single-pane window system in the example above with 1/2-inch triple-pane windows would cut the BTU loss to 480.