Energy efficient windows are a great way to save money and gain control over the temperature in your home. The U.S. Department of Energy (DOE) estimates that the amount of energy lost in the United States through windows is roughly $35 billon annually. That’s a lot of money! The DOE has also cited that most Americans could reduce their monthly heating and cooling bills by 30% by switching from conventional to energy-efficient windows.
Let’s explore the key components of what makes a window energy efficient. There are a variety of performance ratings that detail how efficient a window is.
The American Architectural Manufacturers Association (AAMA) defines the overall performance of a product and provides a numeric rating for each product they review.
The R-Value determines the thermal resistance of your window. How effective your window resists heat conduction and thermal rays is explained by the R-Value rating. The higher the R-Value, the more energy efficient the window.
The U-Factor measures the insulation of your window. By detailing the rate at which heat and air transfers, you can determine the insulation effectiveness. This is the most important aspect to consider in making sure you keep cool air in, hot air out, and money in your pocket. The National Fenestration Rating Council (NFRC) is a non-profit agency that provides and oversees the performance and efficiency ratings on windows, doors, and skylights. According to the NFRC, a good U-Factor generally ranges from 0.25 to 1.25. The lower the U-Factor, the better the window is at insulation.
The next performance standard for window efficiency is the Solar Heat Gain Coefficient (SHGC). This measures the amount of energy that is transmitted through your window by solar fraction. How well your window blocks solar rays, and therefore heat, is measured by the SHGC. While most people often try to remedy a poor SHGC by adding blackout curtains or window shades, those will only block out the light, not prevent the solar heat from penetrating your widows. The SHGC is measured on a scale of 0 to 1 and typically ranges between 0.25 and 0.75. Just like the U-Factor, the lower the SHGC, the less solar heat is transmitted through.
Air Leakage measures the rate at which air passes from outside to the inside of your window. There are numerous joints in the lining of your window where air often finds its way into your home. Some household remedies like caulking or weather-stripping the sides of your window can help, but their effectiveness is limited; nothing can replace quality windows. The rate of air leakage is measured in cubic feet of air passing through one square foot of window space per minute. The lower the air leakage value, the more efficient your window is. 0.3 cf·m/ft² is the standard for most building codes so anything lower than that indicates a high level of efficiency.
The Visible Transmittance (VT) is the performance rating that indicates the amount of light your window lets through. Some windows improve their VT rating by adding degrees of shading while others add layers of glass. VT is also measured on a scale of 0 to 1. Generally, most ratings range from 0.25 to 0.75. The lower the VT rating, the less light is let in.
The last performance rating for the energy efficiency of a window is the Condensation Resistance. This measures the resistance level of water build-up which can occur when it rains, when there is condensation in the morning, or water runoff on your windows. The better your condensation resistance, the more efficient your window will be. This is rated on a scale of 0 to 100 and unlike most of the other ratings, the higher the condensation rating, the less water build up that the window will allow.
There are a variety of factors that affect these ratings and make a window more or less efficient:
The frame affects your window’s resistance to heat conduction and air leakage. The more secure your frame, the more efficient your window will be. Most energy-efficient windows are made of wood, aluminum, PVC, or fiberglass.
The glass of your window affects how well solar radiation is absorbed or let through. There are reflective coatings that can be added to make your window more efficient, and double- and triple-pane windows are the best at blocking heat and light.
The overall design also plays a key role. How secure your window is, the climate it is surrounded by, and the shape of your window will impact its energy efficiency. The better your window is at resisting water and air, the more you will save on your energy bills.
Installing energy-efficient windows is a wise investment to keep your home comfortable and your money from leaking out the windows! Your best bet is to contact a window professional that specializes in energy-efficient windows.
Author Bio: Natalie McCatty is a professional blogger for XO Windows, Arizona’s largest window distributor. Read more about getting the most out of your windows on the XO Windows blog.