Evaluating Energy Efficient Windows
Many Houston Texas homeowners would like to know more about the energy efficiency of their windows. Most of the new replacement windows are labeled to indicate their energy properties but this information may not be available on existing or older windows. Below is an energy efficiency checklist to help you with the process of determining the energy efficiency of your home windows.
The Energy Star Label
First try looking for products that have earned the Energy Star label. The Energy Star label indicates that the window meets energy performance recommendations set by the US Department of Energy. The label includes a map of where the specific window qualifies for the specific climate zone. Windows that are Energy Star qualified should typically meet or exceed energy code requirements for your area. The determining factors for qualification criteria for Energy Star windows is based on your the climate and location of your home.
The NFRC Window Ratings Label
Check for window ratings and energy efficient properties on the NFRC Window Ratings Label. The National Fenestration Rating Council (NFRC) label is needed for verification of energy code compliance. The NFRC label displays whole-window energy properties and appears on all products in the ENERGY STAR program providing a reliable way to determine the window’s energy efficiency properties.
Check the windows for any energy performance labels and information on window performance. If there are no labels or you cannot find any information on the window, you can visually inspect the window to determine the assumed window energy performance with the following:
1 – Verify how many panes of glass the windows has, with each pane of glass comes additional energy efficiency
2 – What material is the window frame made from (aluminum, wood, vinyl). Windows made with wood or vinyl frames insulate better than metal-framed window options so are more energy efficient.
Below are charts to help in assuming the U-factor and solar heat gain coefficient (SHGC). The U-factor is a measure of non-solar heat transfer (like heat escaping in the winter). A lower U-factor is better (lower means less heat loss). The SHGC indicates how much heat from the sun enters through a window. A low SHGC is more important in the hotter climates like the Houston Texas area. The U-factor and SHGC of a window are shown on the NFRC label. Energy Star windows meet the recommended values shown here:
Below is a chart you can reference using the information collected above for the assumed U-factor and SHGC values. This information is based on the International Energy Conservation Code and does not account for features you may not be able to verify such as low-E coatings, gas fills, etc).
3 – Does the window glass has low-E coatings? Low-E coatings are invisible heat barriers that improve window energy efficiency. The most reliable way to identify these coatings is to use a low-E detector device (equipment energy auditors may use). Chances are you do not own one of these but you may be able to identify low-E glass by using a lighter flame or white card by holding either up to the glass and looking for the two reflections from each pane of glass. If one of the panes looks bluer than the other, this is an indication of a low-E coating on that surface.
4 – Does the window have an airtight fit and weatherstripping. Check the sashes and weatherstripping as these are important factors. The windows may have air leakage if they are not fitted tightly or air could be leaking from in between the interface of the frame and the wall if they were not properly sealed during installation. This may be difficult to check for on existing windows.
Professional Window Installation
If you are ready to replace your windows, remember the importance of proper installation of your new energy efficient Energy Star rated windows. This is most necessary for optimal performance of energy efficient windows, to ensuring there is an airtight fit and to avoid water leakage. Use experienced professionals for your window selection and installation.
Additionally, check the Department of Energy for info replacing windows with energy efficient windows that are Energy Star rated.
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