How to Choose Energy Efficient Windows


If you are thinking about investing in new windows for your home or office, you may be overwhelmed by all the options available on the market today. If you are shopping at a major home store and just looking for an inexpensive option, this article may not be for you. This article will help you if thermal performance and energy efficiency, ultimately leading to cost savings is what you are after.

  • I can't tell you everything there is to know about window performance in one article, but this will get you started asking the right questions and will give you enough understanding to make an informed choice. First, let me say that almost all of a window's performance is based on the type of glass and spacer used inside the frame. Of course you want a good frame with a great seal, but the real energy efficiency comes from the insulated glass unit, or "IG", used in the window.

  • An insulated glass unit is made up of panes, or "lites", of glass and a spacer system which seals the interior air space and holds the two lites together. A spacer should include a good sealant which will keep the moisture out, and on the inside, a desiccant, which will wick up any moisture that may have been in the air when the unit was sealed. (This will keep it from fogging up.) A good spacer system will come with a warranty. Make sure you ask about this. A typical warranty is about 10 years, but can range up to 20 years. Oftentimes, the company making the windows does not produce the IG units--sometimes they do. If they purchase the IG units, a warranty should be extended to them which they can then transfer to the buyer.

  • Choosing the right type of glass is possibly the most important step in picking a window with great energy efficiency. The glass you choose will depend on your budget, the availability of the glass, and where you live. Many window and door manufacturers may not be familiar with the specific performance of different glass combinations, especially if they do not manufacture the IG units, however, this information should be available to them by making a simple phone call to their supplier.

  • Typically a residential home will need no more than standard "low-e", double pane windows. PPG Industries (AKA the Pittsburgh Plate Glass of old) makes some really great low-e products. This glass is produced by adding a special coating to clear glass, improving the thermal performance. The best of these two products are Solarban 60 and Solarban 70. The magic of these coatings is that they help retain heat in the winter and keep heat out in the summer. Solarban 70 may sound like the better of the two products, but it depends where you live. In the Southern areas of the U.S., Solarban 70 performs better, but in the North, there is no performance gain. Another note: while it may seem like sound logic that if one piece of coated glass is good, two pieces are better, this is not the case. Double low-e windows do not perform any differently than units with one single piece of low-e glass.

  • Another aspect of a window unit that will effect performance is the air space fill gas. Although many windows have regular old air in between the panes, some are filled with Argon gas, and even fewer are filled with Krypton gas. Argon is heavier than air, and is pumped in between the two panes of glass before it is sealed. It will increase the efficiency of the unit. Krypton has even better performance than Argon, but the benefits do not usually outweigh the prohibitive cost associated with Krypton. Krypton is almost 1000x more expensive than Argon and you will be hard pressed to find it used in residential windows.

  • The size of the space between the panes of glass also has a great effect on the performance of the unit. Air is a fantastic insulator under the right circumstances, and the larger the space between the two panes of glass, the better the performance. A unit with a larger air space with no gas fill can outperform a unit with Argon gas and a smaller air space.

  • PPG has a great tool on their website for comparing the different combinations of glass and gas fills. This tool is really meant for people in the industry, and PPG DOES NOT MAKE WINDOWS so you will have to find a window and door company who uses PPG glass if you like what you see. But this tool can still be useful to a residential consumer if you keep a few things in mind. See the tips below for the website address and more information on how to use the calculator.

  • Many people are shopping for green products for their homes to help the environment and save money on energy. Perhaps you might look for the Energy Star label on a product to tell you that it meets these kinds of standards. There is something important to know about Energy Star and windows, however. Energy Star will be changing the requirements for windows in the near future because the current standards (which were once met only by the highest quality windows) are now being met by almost all window manufacturers. Energy Star is meant to denote the best and most efficient products, so their guidelines will be more stringent in the future. If you want to be on the cutting edge, consider triple pane windows for your home. These will most likely meet the new standards whereas it will be difficult to qualify with a double pane unit.

Tips & Warnings

  • PPG Performance Calculator can be found at:
  • This calculator includes commercial as well as residential products, so many of these combinations will not be available to the residential consumer.
  • Stick with glass thicknesses under 3/16". Anything larger is usually considered commercial, although 1/4" glass may be used residentially under special circumstances.
  • Overall thickness of a unit should not be more than 1" typically. To calculate the overall thickness, add the thickness of the two pieces of glass and the air space. For instance, two pieces of 1/8" glass equals 1/4". The air space can then range from 1/4" to 3/4" in order to keep the overall thickness of the unit under 1".
  • For residential units, you will not find a lot of colors available. Stay with the following options: Clear, Solarban 60, Solarban 70, Sunclean, Sungate 100, and Sungate 500.
  • Feel free to send me any questions you might have, I am happy to help!

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  • Photo Credit PPG Solarban 60 Thermal performance
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