According to Energy.gov, the average American household wastes energy due to drafts, air leaks and inefficient heating or cooling systems. Much of this energy is lost through windows. Replacing windows with new, energy-efficient models helps maintain a comfortable environment in your home, reduces your energy bill and improves your home’s value.
In older windows, outside air can infiltrate through cracks and may cause your heating and cooling systems to work harder to maintain a consistent temperature. This in turn can drive up your energy usage, and have a substantial effect on your energy bill.
Properly insulating walls helps, but Energy.gov estimates that up to 20 percent of unwanted external air enters homes through windows. Installing storm windows and ENERGY STAR®️ windows can reduce heat lost to air leaks by 25 to 50 percent.
Are your windows wasting energy? Here are some signs that you may need to replace your windows with more energy-efficient alternatives.
The benefits of energy-efficient windows go beyond saving money on utility bills. The Efficient Windows Collaborative lists plenty of other benefits, including these:
If you’re considering replacing windows, you need to understand how to read window performance ratings. These ratings describe a window’s energy properties and include such measurements as U-factor, solar heat gain coefficient and visible transmittance. While a little intimidating at first, these factors are easy to understand once you know what they mean.
Window performance ratings are issued by the National Fenestration Rating Council (NFRC) and ENERGY STAR®️. The NFRC tests and certifies windows, doors and skylights based on their energy performance ratings. Participation in the program by window manufacturers is voluntary.
ENERGY STAR®️, in contrast, is a government program with stricter demands than the NFRC. While all ENERGY STAR®️–certified windows include the NFRC label, the reverse is not always the case. ENERGY STAR®️ windows are rated on U-factor and solar heat gain coefficient ratings.
Learning to read a window energy performance rating helps you choose the right windows for your home. Physical location has a significant impact on which aspects of an energy performance rating matter most to you.
Pro tip! Check the Efficient Windows Collaborative website for advice on choosing ENERGY STAR®️ windows appropriate for your state.
Here’s what each part of a window energy performance rating means:
U-factor describes how fast a window conducts heat from inside the house to the outside air. The lower the U-factor, the better the window’s insulating value and the slower the transference of heat.
U-factor ratings may refer to the glass and glazing only, but NFRC ratings consider the U-factor of the window frame as well as the glass.
Solar heat gain coefficient (SHGC) refers to how much solar radiation passes through a window. SHGC is expressed as a number between 0 and 1. The lower the rating, the less solar radiation passes through the window.
Whether you need a high or low SHGC rating depends on your location. Homes in northern climes may benefit from a higher SHGC, which helps transmit the sun’s heat into the home during the winter. Windows with a lower SHGC are better suited to hot, sunny environments. The home’s orientation and proximity to shade trees can also affect how high an SHGC rating is needed.
Visual transmittance (VT) describes how much light is transmitted through the window. The higher the visible transmittance rating, the more light gets through.
VT ratings include the effect of the frame on light transmission as well as the window glass. VT ratings range from 0 to 1, with most windows having VT values of 0.3 to 0.7.
Air leakage is self-explanatory: it’s a measurement of how much air passes through a window. AL is measured in terms of how many cubic feet of air will pass through a square foot of window area, but all you really need to know is that the lower the AL, the less air leaks through cracks in the window assembly.
Condensation resistance (CR) refers to how well the window resists the formation of moisture and condensation on the interior surface. CR is rated on a scale of 1 to 100, with higher ratings indicating greater resistance.
As condensation resistance is an optional rating on NFRC labels, you may or may not find it listed as part of a window energy performance rating.
Replacing windows represents a significant financial investment. You therefore want to choose the right windows for your home the first time. Your choice depends on climate, your home’s physical characteristics and your style.
When shopping for windows, Energy.gov recommends considering the following factors:
Windows come in a wide range of styles. The style that’s best for you may not be right in a different climate or even a different house. Durability, price and your personal preferences all influence what makes the best energy-efficient window for you.
Double-hung windows open by sliding panes up and down. Casement windows, in contrast, open outward like a door when you turn a crank on the side of the window.
Casement windows tend to be more energy efficient than double-hung windows. When compared to double-hung styles, casement windows allow less air leakage because the closed sash presses equally on all sides of the frame, sealing the window like a door.
Double-hung windows usually only fit tightly on the frame’s side tracks, so air can leak out of the home at the top of the window frame. If you choose double-hung windows, proper insulation can help prevent leakage.
Are sliding windows energy efficient? Think about sliding doors—they’re not as energy efficient as hinged doors, which fit snugly on all sides of the doorframe. This comparison extends to sliding and casement windows.
Like double-hung windows, sliding windows don’t grip their frames as well as do casement windows, as the sash slides horizontally to open and close the window. Weatherstripping can minimize air leakage, but if saving energy is your main goal, casement windows win the day.
Single-hung windows have only a single movable sash that slides vertically. The upper sash on the window cannot be moved as it can in a double-hung window. Because only one sash moves, single-hung windows tend to have less air leakage than slide windows.
When replacing a window, homeowners have the option of a newly constructed window or retrofit window replacement. The two methods are very different. When you retrofit windows, the windowpane is replaced, but the surrounding framework is left intact.
A newly constructed window reconstructs the window’s framework and may require replacing parts of the wall. Of the two methods, installing a newly constructed window is the more expensive option.
Retrofitting windows is a less complicated project and generally less expensive than a newly constructed window. As the window is installed in the existing frame, homeowners only need to consider the glass pane’s U-factor and SHGC ratings.
Retrofits do have some drawbacks. As the window is installed inside the existing frame, it tends to be slightly smaller than the window it replaces, potentially reducing the amount of solar energy and light that enters the room.
It’s also important to consider the condition of the existing frame before retrofitting your windows. If the existing frame is warped or damaged, then an installer may need to repair or replace the window frame to prevent any potential leaks.
New construction windows are a more expensive option than retrofit windows, as the original window frame is removed and reconstructed. If the surrounding wood and studs are damaged, they must be repaired before installation, which can increase costs.
New window frames, however, are less likely to leak and are often more energy efficient than the frames they replace. New construction windows also tend to offer a larger view than do retrofitted window panes.
One of the greatest advantages of retrofitting a window is that the project can be completed by an experienced DIYer. If you’re not comfortable with your DIY skills, a window professional can easily retrofit windows. Replacement windows come in two basic varieties: flush fin and block frame.
Below are the basic steps needed to replace windows during a retrofitting project. Bear in mind that each window replacement is different. Depending on your project, you may need to take additional steps.
Installing a new construction window is much more complicated than retrofitting and, in most cases, is a matter best left for professionals. However, if you’re an experienced DIYer and are keen to try, here are a few tips for how to approach the task.
Installing a window—especially a newly constructed window—is a complex task. Don’t be shy about hiring a professional if you don’t think you can complete the project yourself. You want the installation to go right the first time.
Replacing old windows with energy-efficient models has so many benefits. You’ll reduce the amount of energy you waste, have a more comfortable home and improve your curb appeal. It’s an investment that’s well worth the cost!
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