Here is the breakdown of where the AIR Escapes in a typical house:

10% Windows
4% Fans and Vents
2% Electric Outlets
31% Floors, Walls, and Ceiling
15% Ducts
14% Fireplace
13% Plumbing Penetrations
11% Doors

Source: U.S. Department of Energy

First of all, it is hard to determine from this article if air loss and heat loss are direct correlatives. It is a fair assumption and very intuitive to assume they are relative. Consider the following information.

With windows, there are 5 major areas of heat gain and or loss. This is what is on the Energy Star Label of windows. They are vastly simplified here and are as follows:

1. U-Value

This is the amount of heat that a window prevents from escaping.

2. Solar Heat Gain Coefficient (SHGC)

This is how much the window heats the house from sun light.

3. Visible Light Transmittance

The amount of sunlight that enters through the window.

4. Air Leakage

How much air gets out of a house through the windows.

5. Condensation Resistance

How much a window will condensate. (Optional)

Source: – The American Council for an Energy-Efficient Economy

The leading research suggests that air loss and heat loss are proportional. Windows and doors are 21% which is almost 1/4 of the air loss through your house.

Another point to consider is that the reason why the Energy Star ratings are different in different areas is that the weather can be extremely different when analyzed. There is anecdotal evidence that some companies that produce windows only apply for a rating in one area.

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