You’ve probably come across advertisements about how new windows can help you save on your energy bills. You’ve also probably wondered how it works, considering that most types of windows do not even require electricity. In today’s post, Renewal by Andersen® of Seattle answers your questions with this primer on how window replacement can translate to energy savings.
The Energy Envelope
Windows are part of a larger structure called the “energy envelope”, which also consists of the exterior walls, the roof and, in some types of buildings, the floor. Together, these components form an enclosure that is heated and cooled by your HVAC system. According to the Department of Energy, space heating and cooling accounts for about half of an average home’s annual energy bills, so if one can cut the house’s comfort requirements to even by half, this could result in significant savings.
The problem with traditional windows is they can defeat well-insulated walls and roofing. Single-pane glass, in particular, allows thermal transfer, which causes heat loss during heating seasons and heat gain during cooling seasons. This makes the heating and cooling systems run for longer times, which adds and results in high utility bills.
Energy-efficient replacement windows are equipped with double-pane glass. The gap between the interior and exterior surfaces acts as an insulating layer that helps slow down thermal transfer and contribute to energy savings over its service life.
Energy Efficiency Ratings
It’s never been easier to find energy-efficient replacement windows — all you need to do is look for the ENERGY STAR® certification label affixed on the windows. If you are looking for a specific feature or a combination of features, look for the following on their energy efficiency ratings labels.
- Insulation. Window insulation is measured by its U-factor. The lower the value, the better the insulation. In some windows, you may instead find R-Value, which measures a windows’ resistance to thermal transfer. This means a window with a low U-Factor will have a correspondingly high R-Value.
- SHGC. Solar heat gain coefficient measures a window’s heat gain from direct sunlight. Low SHGC values mean better resistance against solar heat gain.
- VT. Visible Transmittance measures how well the window allows natural light into the building. Thanks to coatings that selectively block UV radiation and solar heat, it is possible to find windows that have high VT ratings (which means more natural lighting) with low SHGC ratings.
- Air Leakage. This measures how much air passes through a closed window. The lower the value, the fewer drafts you’ll experience.
Just as important is the quality of the installation — even the most energy-efficient windows won’t function as designed if not installed properly. Our team at Renewal by Andersen of Seattle can discuss energy savings and other benefits of energy-efficient replacement windows through a no-obligation consultation. Give us a call at (206) 777-0954 or fill out our contact form to schedule an appointment. We serve communities in Seattle.