A question that often arises is whether or not Low-E Windows are energy efficient and will they reduce my energy bill? The term Low-E refers to materials that have low thermal emissivity, meaning that the material reflects a high percentage of radiant thermal energy and allow just a small percentage of thermal energy to pass through. So in the case of a Low-E window, the answer is simple: Yes Low-E windows are energy efficient and yes, Low-E windows will reduce your energy bill each month.
In recent years window manufacturers have developed Low-E coatings that greatly reduce the amount of infrared and ultraviolet light that can pass through the glass. While at the same time, the coatings allow ample daylight to pass through the glass. By comparison clear, uncoated glass can have an emissivity rating of 0.84. Meanwhile, some of the energy efficient Low-E glass on the market today can have an emissivity rating as low as 0.03 or even 0.02.
So how will Low-E Windows Reduce my Energy Bill?
By reflecting a significant amount of solar infrared energy, Low-E Windows can reduce your energy bill year round. In the summer the Low-E coating will reflect the heat of the sun and help to keep your home cooler. Your Air Conditioning unit will work less, saving you money.
In the winter months the opposite scenario occurs. The warmth of the interior of your home tries to escape through your windows. The Low-E coating on your windows will reflect the heat back into your home. By reducing the time your furnace operates, you will lower your monthly energy bill.
Are all Low-E Windows the Same
Not all Low-E Windows are created equal. The ratings of Low-E windows will vary from manufacturer to manufacturer. While virtually all Low-E windows are very energy efficient, there are subtle differences in the materials used and how they are applied, which can affect the rating. Here are the values you need to look at when comparing products:
- U-Value: This is the rating of how much heat loss the glass allows.
- VLT: The VLT or Visible Light Transmittance is the amount of light that is allowed to pass through the glass.
- SHGC: The SHGC or Solar Heat Gain Coefficient is the amount of solar radiation that is allowed to pass through the glass. A window with a lower SHGC will transmit less solar heat.
- LSG: The LSG or Light to Solar Gain is a number that represents the ratio between the SHGC of the glass and its VLT rating.