 
Windows
 Windows are a major source of heat
loss in the winter and heat gain in the summer. Although clear
glass is durable and allows sunlight to enter a home, it has very
little resistance to heat flow( R-value). R-values for windows
typically range from 0.9 to 3.0, and these five factors
affect the R-value:
- Whether the glazing material is glass,
plastic, or treated glass. (Glazing refers to the cutting and
fitting of windowpanes into frames.)
- The number of layers of glass. Single-pane
glass has an R-value of about "1," and accounts for much of the
heat loss/gain in the home. Double and triple-pane windows have a
layer of air or gas between the panes to resist heat flow.
- The size of the air space between the layers of
glass. Air spaces above 5/8 of an inch and below 1/2 inch
have lowered R-value because they allow too much heat to transfer.
- The thermal resistance or
conductivity of the frame and spacer materials.
- The "tightness" of the installation
Because windows are a major investment,
choose your frames and glazing materials carefully.
No one window is suitable for all situations, and a combination of
styles and materials may be necessary for enhanced efficiency.
Examine your particular heating and cooling needs
before you buy!
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