Window, window, in the wall...

...which is the most efficient of them all?

Well, it's time to do some window research again...this time I'll try to take notes so that I don't forget everything again...My first stop for windows research has always been energyefficientwindows.org. Reading through their pages and using their window selector, it seems that we want the following windows:

• on the south side - window 30:
  double-glazed, high-solar-gain, low-e, argon gas, insulated vinyl
  (U value of 0.29, SHGC of 0.56 and VT of 0.58).
• on the east/west sides - window 33:
  triple-glazed, moderate-solar-gain, low-e, argon gas, insulated vinyl
  (U value of 0.18, SHGC of 0.40 and VT of 0.50)
  

The U-value indicates how well the window insulates (i.e., keeping the heat in); the Solar Heat Gain Coefficient (SHGC) indicates what percentage of the sun's energy is allowed to get through (and heat our cement slab and other thermal mass); the Visual Transmittance (VT) indicates how much "dayligh" makes it through the window (the lower, the darker).

As I see now, "Insulated Vinyl" has become as energy-efficient as our previously favored Fiberglass. The challenge will be to find a company that makes windows with these characteristics, because it seems that this model windows are just hypothetical windows and don't represent any physically available windows...


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