Why Energy Performance Ratings Are Important When Choosing New Windows
Windows, doors, and skylights face an age-old problem: when they let a lot of light in, the house overheats. When you are shopping for a window, door, or skylight, you want to pick a window with a rating that is suited for your climate.
Here are the ways we measure glass insulation. Not all of the ratings are better when they are higher, but a few are.
With windows, doors, and skylights, we measure several factors in the quality of the glazing and the overall performance of the product.
What Is a Good SHGC Rating?
This depends on your climate. Different SHGC (solar heat gain coefficient) ratings reflect how well the window is suited to hot or cold climates. Choose a high SHGC rating for colder climates and a lower one for hotter climates.
What Is the Most Energy-Efficient Glass Windows?
The most energy-efficient glass is the one that has the lowest U-factor. You don’t necessarily want your house heating and cooling with the weather! Choosing a well-insulated glass that has a low NFRC U-factor is the best way to go.
This type of rating, as opposed to a regular U-factor, is inclusive of the whole window, door, or skylight rather than just the glass.
There are many types of glass and treatments on windows. It seems there are an infinite number of frames as well. Be sure to talk to an expert about the type of insulation value you need and how much light you are looking for in your home.
Measurement of Heat Gain and Loss
Windows and doors can gain and lose heat in several ways. There is regular conduction through the glass, frame, or door.
There is the radiation of heat in (from the sun) and out (from people, walls, and furniture).
Then there is air and energy that leaks through and around windows, doors, and skylights.
People measure heat gain and loss by three standards. They measure the U-factor, which is the rate at which a window, door, or skylight will conduct heat flow that doesn’t come from the sun.
It is usually written as BTUs over hr-ft2-degrees(F). In most cases, the U-factor measures just the glass. But for an NFRC U-factor, it will measure the whole window, skylight, or door. The lower the U-factor, the better.
The Solar Heat Gain Coefficient, or SHGC, is a measurement of the solar radiation that gets through a window, door, or skylight. It can be let indirectly or absorbed. A high SHGC rating means that a product is better at collecting solar heat during the cooler months.
A lower SHGC rating is better at blocking solar heat during the hot months.
Air leakage is a measurement of how much air gets in around a product. We measure it as units of cubic feet per minute per square foot of frame area (cfm/ft2).
Letting In Light
Visible Transmittance, or VT, is the measure of the light on the spectrum that humans can see with our eyes that gets in through the glazing. The number will be between zero and one, with more light coming in closer to one than zero.
Light-to-Solar-Gain is a ratio of light transmittance to blocking heat gains. It is the ratio between SHGC and VT. A high number indicates more light without too much added heat. This isn’t always easy to find for many products.
Keeping Water Out
Windows are rated on a scale of zero to 100 for Condensation Resistance as well. The higher the rating, the less water collects on the window.
Shopping For New Windows With The Right Expert
Always take a certified technician with you when you go shopping for windows, doors, and skylights. There’s a lot to know and a lot to read! At Cheney Window & Doors, our new window experts are here to make sure that you get exactly what you need for your home.
Cheney Window & Doors is Oakville’s one-stop-shop for everything windows and doors.