For the greatest energy efficiency, you need different window glazing on each side of your house. West-facing windows are generally susceptible to heat and glare from low afternoon sun; east-facing windows in hot climates are similarly vulnerable in the morning. In the northern hemisphere, the solar heat gain through south-facing windows may be welcome in winter; you might select high Solar Heat Gain Coefficient (SHGC) windows for this facade if you also plan to shade these windows in summer. North-facing windows receive no direct sunlight during winter in most of the United States, but they are vulnerable to winter heat loss, so it’s worth going for a low U-factor even at the expense of a lower SHGC—which can also help reduce summer heat gain.
By choosing the best windows for each side of your house, you can increase your year-round comfort and lower both your heating and cooling bills. While there are window qualities that are generally the best for each facade, always take your local climate and your shading situation into account.
Note that if you choose different glazing for each side of your home, you’ll be an unusual consumer. Most window companies want to sell one product for all four sides. You’ll also want to make sure your contractor reads the window labels and installs your carefully chosen windows in the correct locations.
Choosing the right windows is not always enough; you may also need shading devices, especially if you’re specifying high-VT, high-SHGC windows. Intercepting direct sunlight before it strikes the window can greatly diminish summer solar heat gain. During hot weather, modest fixed overhangs, awnings, or trellises on the south, and exterior shading devices on the east and west, will produce the best energy performance in most parts of the country.