For your replacement window, Seattle Glass Doctor suggests using ENERGY STAR® or higher rated windows to reduce your energy bills by 7 to 15 percent (according to ENERGY STAR's website).
Not only that, but replacing your Seattle windows with energy efficient glass fixtures lowers your carbon footprint with less energy use and fewer emissions. As a bonus, ENERGY STAR rated windows can get you up to $200 in a federal tax credit.
To be an ENERGY STAR rated window, your replacement window requires:
U-Factor less than or equal to 0.30 or 0.32 Solar Heat Gain Coefficient (SHGC) of greater than or equal to 0.40
South-facing Western Washington windows ideally have a higher solar heat gain coefficient (SHGC) and a lower U-factor in order to decrease heat loss.
East and West (West especially due to summer sun) facing windows should be shaded or have a lower SHGC
Windows facing the North get little direct sun, making SHGC of less importance. A low U-factor is ideal for North windows to lower heat loss.
