Why Energy Efficient Windows?

Why Energy Efficient Windows?

 

 

Why Energy Efficient Windows?

 

Want to save energy in your home? The single most important step is upgrading to energy efficient windows. Old windows, especially wood and aluminum, are notoriously the weakest link in efficiency for any home.

Who are the culprits?

You can blame the glass or glazing in your window. Most older windows are single-glazed, or a single glass pane-thick. Newer energy efficient windows are double or triple-glazed, containing two or three panes of glass hermetically sealed together to prevent air flow. The more glazing, the more energy efficient.

What makes energy efficient windows so great?

* New window manufacturers add coatings or gases between the panes to prevent certain wavelengths of light (solar heat) from entering. This saves you energy.

* Many double-glazed windows have argon gas sealed in between the panes to prevent heat loss.

* The most effective coating used on the glazing itself is called Low-e, or low emissivity, coating. Low-e coating is a thin, nearly invisible coating applied to the glass (or sometimes suspended between two panes) that allows visible light to penetrate, but bars radiant heat waves from doing the same. It also keeps heat inside during the winter months. Low-e coatings are available for application to existing windows to improve energy efficiency (albeit with slightly less effect) without completely replacing the windows.

Windows with low-e coating can save up to 30-50 percent more energy than those without it.

How do I know how efficient my windows are?

You can check the labels stuck to new windows from the National Fenestration Rating Council (NFRC). There are several specifications relating to energy efficiency:

* R-value measures the amount of heat lost through the window glass. It’s the same value you’ll find given for the insulation in your walls, doors and any other home product that holds some insulation value. R-value for windows is quite simple. A single-glazed window will have a value of R-1, double-glazed will have an R-2, triple-glazed R-3 and so on.

* U-value is similar to R-value but with time included in the equation. U-value represents the amount of heat lost through the window per hour. U-values show up in the form of decimal points (typically from .20 to 1.20) and the lower the U-value, the more energy efficient the window is.

* Solar Heat Gain Coefficient is a measurement of how much heat the window lets in along with visible light. For homeowners in arid/warm areas or anyone with south facing windows, this is especially important. The lower the coefficient, the less heat is allowed in.

* Visible Transmittance measures on a scale of 0-1 how much light the window allows to pass through. A lower number equals less light.

* Air Leakage (AL) number is vital to a window’s energy efficiency, as this is the reason for the cold drafts from older windows and a top reason why families look to replace those windows. Air leakage is not limited to the window glass; it includes seals, joints, frame, and anywhere that air can pass through. Look for a low AL number – these are the windows that best keep air in or out of the home and reduce the load on your heating & cooling system the most.

All of the above information should be readily available, if not visible on the window itself as it sits in the showroom or warehouse. Another key symbol to look for is the Energy Star label, representing an efficiency standard put together by the US Department of Energy and a must-see if you are hoping to recoup some of the purchase and installation costs by way of energy efficiency tax credit.

 

 

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