What Makes A Window Energy Efficient?
Northwest Energy Savers:
What Makes a Window Energy Efficient?
Northwest Energy Savers wants you to know what makes a window energy efficient so that you can make an intelligent decision, based upon facts, not sales hype.
Remember: Just because a window is dual paned does not make it energy efficient!
The bottom line in energy efficient windows is trying to allow the LEAST AMOUNT OF HEAT to pass through your windows. In the Summer we want to keep the heat out, in the Winter we want to keep the heat in.
A window is made up of three main parts:
- FRAME: Material the window is made of – wood , vinyl, composite
- SEAL: What is between the two panes of glass including the Spacers, such as Aluminum, Intercept, Swiggle Seal, and Super Spacer.
- GLASS: What type of Glass is used is VERY important such as: LOW-e glass- Low emissivity glass. This is specially treated glass that reflects the heat that normally passes through regular glass yet allows much of the light to still come through.
If a window is energy efficient it should have an “Energy Star” rating from the EPA.
In order for a window to qualify for “Energy star”, it must have a U-factor of Below .30 and an SHGC of Below .30
The Lower the numbers, the better the window. Remember, just because a window is dual pane, does not mean it is “Energy Star”. This rating also qualifies the windows for a tax credit of up to $1500.00.
For more info on the EPA Energy star program click here www.energystar.gov
See below for a comparison of U Factor and R Value.
The NFRC National Fenestration Rating Council was formed in 1992 to develop a uniform test to help Homeowners make an Intelligent Decision regarding the purchase of Energy Efficient Windows.
Windows are tested in several areas including:
- U-Factor: How well does the window keep the heat in – How well does it perform in the cold weather.
- SHGC: Solar Heat Gain Coefficient – How well does it keep the solar heat out.
These numbers are usually noted right on the window itself. It should also be on any material published by the window manufacturer.
THE LOWER THE NUMBERS ON THE TEST, THE BETTER THE WINDOW. If a window rates lower than .30 U-factor and .30 SHGC, it qualifies for the EPA rating of “Energy Star”.
For more detailed information about the NFRC
click here www.nfrc.org
Relationship of U factor to R value
In walls we measure insulating value by an “R” value, the higher the number the better the insulating value of the material. In walls the measurement is for how well cold is kept out of the house. With a window the measurement is for how well the heat is kept in the house. R value is the reciprocal of the U factor; ie: U factor of .30 = 3.3 R value.(How many times does .30 go into 1?) For more detailed information go to the Ask Window Guy Blog.
