Solar heat gain coefficient is how the reflective qualities of the Low-E glass is rated, Low-E glass (E stands for emittance) is the multi layered coating of your new energy saving windows, as important or more important than the U-factor of the whole window. The slowing of heat transfer across the insulated glass units with Low-E glass is vital to the energy saving of your home. It always reflects the heat back to its source. The lower the number the better the reflective qualities of the Low-E glass package that works in summer and also the winter.
Low-E Coating in Summer.
In the summer months the Low-E reflects the solar heat gain from the suns rays along with the long range heat waves from the hot roads, sidewalks and automobiles away from your house and keeps it outside, allowing your home to stay cooler and the A/C running less.
Low-E Coating in Winter.
Heat is always drawn to cold, trying to heat the cold. In the winter Low-E reflects the heat that is trying to radiate out through the glass back into your house. This keeps your windows and home a lot warmer and the furnace running less, saving you money on your winter energy cost and keeps you a lot more comfortable. If you notice it only reflects heat, it reflects the long range heat waves back into your house.
Energy Star SHGC Rating.
The Washington Metro area is in the north central area of the energy star map. Energy star rated windows must have a solar heat gain coefficient of .40 or below and in the south and south central it must be .25 or below. However it seems we have hotter than normal summers in this area and Thermal Specialties recommends the solar heat gain coefficient to be .25 or better for summer and winter comfort.
Ultra Violet Light.
Low-E glass also reflects more than 50 to 70 percent of the suns damaging ultra violet light from getting into your house and fading your furniture, carpeting, shades, curtains, paintings, photos, wood flooring products and all your family’s treasured items.