I have a west facing window. How can I get max light while avoid any heat coming from it?


To reduce heat gain from the sun, you need a window with a good "low e" rating (also called low emissivity). You can get similar results on an existing window by adding a film that reflects IR.

You also want multi-layer windows to block heat transmission (a lower U value is better, it's the inverse measurement of an R value you see on insulation). And finally, you should make sure that the window has good weather stripping to block any drafts, causing a direct heat loss/gain to your home.

Here's an article that describes this in more detail.

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You may want to try an after market installation of some of the newer low E films before replacing a window with factory applied coating.

You have 2 competing factors that cannot both be optimized: Visual transmittance (VT) and Solar heat gain coefficient (SHGC)

Two measures of a film’s energy performance are visible transmittance (VT) and solar heat gain coefficient (SHGC), which range from a unitless measurement that is between zero and 1. A higher VT value indicates greater amount of visible light passing through the film, while a lower SHGC means more solar radiation is rejected by the film. Mid-range products with VT and SHGC values around 0.5 are “ideal for northern climates,”


Films where VT greatly exceeds the SHGC are suitable for hot climates

Excerpted from Eco building pulse article

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