How Are Windows Rated For Efficiency?
One of the main considerations that homeowners and contractors look at when reviewing options for a window replacement project is the energy efficiency of the new windows. To make it easier for homeowners to select the most efficient windows, accredited agencies in Canada have designed energy performance ratings for windows.
Checking the energy performance rating of windows before making a buying decision can mean the difference between keeping energy costs to a minimum and consistently increasing energy bills.
Energy performance in replacement windows is rated using a number of values which include U-factor, energy rating (ER), R-value, solar heat gain coefficient (SHGC), visible transmittance (VT), and centre-of-glass rating.
Here is a look at each of these values in detail.
Also known as u-value, the u-factor measures the rate of heat transfer through the window assembly which includes the glass, window frame, and spacer. In other words, the u-factor describes a window’s ability to keep heat inside your home. This value tells you how well a window insulates. A lower value means better energy efficiency.
U-factor values for windows range from 0.25 to 1.25, and they’re measured in watts per square metre Kelvin (W/m2K). Generally, replacement windows with a lower U-factor are preferred, especially if you are interested in lowering your energy consumption and bills. Replacement windows with a low u-factor are available in a wide range of styles and designs, so finding an option that matches your home shouldn’t be an issue.
2. Solar Heat Gain Coefficient (SHGC)
This value measures the amount of solar radiation that passes through the window. In other words, the solar heat gain coefficient tells you how well the window blocks heat caused by sunlight. The lower the value, the less solar heat the window transmits, and the higher the value, the more solar heat the window transmits. SHGC ranges from 0 to 1.
The type of glass used to make a window determines its solar heat gain coefficient. Generally, windows with a high SHGC help to keep your home warm during winter months, and those with a low SGHC help to keep your home cool during the summer months.
3. Visible Transmittance (VT)
Visible transmittance measures the amount of visible light transmitted through a given window material. It is expressed as a percentage. The lower the percentage, the lower the amount of visible light that can pass through the window material.
R-value refers to a window’s ability to retain heat. The higher the R-value, the better the window is at resisting heat conduction through the window. This keeps the heat in your home during the winter, and the heat out of your home in the summer.
5. Energy Rating (ER)
This value measures a window’s performance based on U-factor, SHGC, and air leakage. The higher the value, the more efficient the window. Energy rating for windows ranges from A to G, meaning A-rated windows offer the highest energy efficiency while G-rated windows are the least energy efficient.
6. Air Leakage
Air leakage measures the amount of air passing through the joints in a window. It is measured in cubic feet or cubic meters per minute. The lower the value, the more airtight the window.
7. Centre-Of-Glass Rating
This value measures the energy efficiency of only the glass portion of a window, rather than the entire window assembly.
Generally, these are the key values used to measure a window’s energy efficiency.
Southfield Windows & Doors specializes in replacement windows and doors in Kitchener and surrounding townships. We offer a wide range of energy efficient replacement windows. Contact us at 519-669-3872 to schedule your free in-home consultation!