With the rising cost of energy in the home, it’s as important as ever to understand how energy efficient your basement windows are. Having an understanding of how this is measured will help you pick the right kind of window for your basement.
Using energy performance ratings you can see that standard of each window when it comes to gaining and losing heat and how well it transmits sunlight into your home.
Basement window manufactures can opt in to a voluntary programme operated by The National Fenestration Rating Council (NFRC). The programme tests, certifies and labels the window based on their energy performance rating. This makes it easier for the consumer to compare products and determine the windows energy properties.
Windows gain and lose heat in many ways. It can be direct conduction through the glass of the window or the frame. Heat can enter the house from the sun radiating through.
The information contained on the label will mean nothing if you don’t understand what they mean and how they are rated.
U-Value (Or R-Value)
This measures how well the product prevents heat from being lost. The rates of the U-value fall between 0.20 and 1.20. The value is a calculation of how much heat is lost, there for the lower this value is the better it is at resisting heat loss and makes for a better insulating window. Although the R-Value isn’t displayed on the NFRC’s labels, it is some times shown on others. There for it is good to understand and not to get it confused with the U-value. The R-value is a calculation of how resistant the window is to heat loss, there for the higher the number the better it is at insulating.
These values are the best way to determine the energy performance of your basement window. This will allow you to compare products when shopping around. All the information on the label will help you compare windows for your basement, but it is the U-value that will really give you a good understanding of the energy performance.
Solar Heat Gain Coefficient (SHGC)
This measures how well the basement window blocks heat from the sunlight. The calculation is the fraction of incident solar radiation admitted in through the window either directly transmitted or absorbed and then released into the home. The values are between 0 and 1, the lower the value the less heat it transmits to the home.
Visible Transmittance (VT)
VT is the measurement of light that comes through the window. This is an optical property and only deals with visible light. This is important depending one which direction the basement window faces and how much you depend on natural light. The value is between 0 and 1, the higher the number the more light is let in.
Air Leakage and Condensation Resistance
These last two values will not help with determining the energy performance of the window, but can be handy to understand. Air Leakage is a value that indicates how much air can pass through the window. It measures the cubic feet of air passing through 1 square foot of the window. So the lower the value, the less air passes through.
Condensation resistance measures the ability of the window to resist condensation forming. The higher the number the better it is at resisting. The actual amount of condensation is impossible to predict as it depends on the environment, so what it does is allows you to compare the windows ability to resist the condensation.