August 27 2009

Why Energy Efficient Windows, Like ENERGY STAR?

by racheal

Energy Efficient Windows

Windows can be the most attractive feature of your home. They offer outside views, sunlight, when open they provide breezes, and solar heating in the winter. Windows, when correctly selected and installed, can minimize a home’s heating, cooling, and lighting costs. However when not properly installed and selected they also can account for 10 – 25% of your winter heating bill through heat loss through the window. If you have single pane windows within the home, as almost half of the U.S. homes do, you might want think about swapping them for a more energy efficient window. This will save you money on your electric bill plus keep a steady temperature through your home all year long.

Cold Energy Loss From WindowsWith new double pane windows and high performance glass available on the market, you have a wide range of styles and models to choose from to suite your needs. If you live in colder climates, pick a window that is gas filled with low emissivity (low-e) coatings on the glass. This reduces heat loss during the colder months.

Controlling air leaks in your windows controls the energy loss within your home. Energy is wasted when air seeps in or out around the windows. You can reduce those air leaks in several ways. The least expensive options are by caulking, weather-stripping, adding storm windows, or replacing the window frames. The more costly ways are to replace the windows completely with energy efficient windows.

Caulking: If you choose caulking and weather-stripping caulks (usually latex or silicone) this fill the cracks and holes which heat and cold escapes form. Before applying new caulk, you should remove any old caulk or paint around the window using a putty knife or a special solvent. Once the old caulk is detached, you can apply the new caulk to all joints in the window frame and the joints between the frame and the wall. The prime time to apply caulking to your window is during dry weather. The idea outdoor temperature should be above 45 degrees F. Low humidity is crucial to prevent cracks from swelling with the moisture.

Weather-stripping: Weather stripping is a narrow piece of metal, vinyl, rubber, felt, or foam that seals the contact between the fixed and movable sections of a window joints. Make should you do not interfere with the operation of the window. 

Storm Windows: By installing exterior or interior storm windows, you can reduce your heat loss through by 25 – 50%. However storm windows need to be weather stripped at all moveable joints.

Heat Loss and Energy Efficient Wendows

An additional option to reduce heat loss and gain insulation is to install shades, shutters, and drapes can be applied on the inside of windows which reduce heat loss in the winter and heat gain in the summer. Shading material such as exterior shutters, awnings, or screens can reduce unnecessary heat gain in the summer. These window treatments are cost effective compared to purchasing energy efficient replacement windows and should be considered first.

If you are looking for a more advance way to increase your energy efficiency, the best way is to buy new energy efficient windows. This is more expensive up front then the pervious techniques, but it will save you more money in the long run, but ENERGY STAR windows qualify for an energy tax credit! Trying to determine which new high tech windows to buy can be daunting however using the standardized labels on new windows will make it easier to shop for energy efficient windows. The National Fenestration Rating Council (NFRC) label may appear on new windows sold.

Located on the windows is the manufacturers use term U-factor as a measure of thermal performance. U-factor illustrates a window’s ability to conduct heat. Window ratings also give an R-value that depicts the insulating rate. The higher the R-value and the lower the U-factor, the more efficient the window will be in keeping your home cool in the summer and warm in the winter. R-values range from 0.9 to 3.0 and U-factors from 1.1 to 0.35. When looking for the R-values make sure the values are calculated for the entire window, including the frame and not just for the center of the glass.  The following five factors affect a window’s R-value: The layers of glass, size of the glass, thermal resistance or conductivity of the frame and spacer materials, tightness of the installation, and the type or glazing material (glass, plastic treated glass).

What are Glazing Materials you ask? Well traditionally clear glass has been the main material for windowpanes in homes. However in recent years, numerous special glazing materials have appeared on the market to help control heat loss and condensation.


Low-Emissivity (Low-E) glass has a unique coating to reduce heat transport through the window. Low-E coatings reflect 40 – 70% of the heat that is normally passed on from the glass to into the home. However Low-E glass still allows the full amount of light to pass through. This heat absorbing glass contains a tint that allows it to absorb as much as 45% of the incoming solar energy and reduces heat gain throughout the home.

Reflective Glasses are coated with a reflective coating that helps control solar heat gain during the summer. This also reduces the passage of light all year long and reduces solar transmittance. This protects your carpet and furniture from fading.

Plastic Glazing materials like, acrylics, polycarbonate, polyester, polyvinyl fluorides, and polyethylene—are also widely available. Plastics can be cheaper, stronger, and lighter then glass. Some plastics also have higher solar transmittance than glass. However, plastics tend to be more vulnerable to the effects of weather.

Glass Layers and Air Spaces Standard are unlike single pane glass windows which have very little insulating and contribute to heat loss and gain. Where double or triple pane windows have insulated air or gas-filled spaces between each pane that resist heat flow. However air spaces that are too wide (more than 5/8 inch or 1.6 centimeters) or too narrow (less than 1/2 inch or 1.3 centimeters) have lower R-values. Superior multi pane windows are built with inert gasses (argon and krypton) in the spaces between the panes. These gases transfer less heat than air does! Keep note though, multi-pane windows are coastlier than single pane windows and may limit framing options.

Framing is also important when it comes to adding energy efficiency in your home. A variety of framing materials are available. Frames can be made of a single material or made with a combination of different materials such as wood, aluminum, clad, and vinyl. Each framing material has its advantages and disadvantages.

Aluminum Frames are ideal for strength and personalized design. Aluminum frames however conduct heat and therefore lose heat faster and assist condensation build up.

Wood Frames have high R-values and are not affected by temperatures extremes and do not promote condensation. Unfortunately wood frames do require considerable maintenance with sporadic painting or staining. Plus if not correctly protected, wood frames can swell and lead to rot and warping.

Vinyl Frames made from polyvinyl chlorides (PVC) offer many advantages. Vinyl is available in a wide range of shapes and styles. Vinyl frames have a modest to high R-values and are easily tailored, competitively priced, and need very low maintenance. While vinyl frames do not contain the strength of metal or wood, you can strengthen larger sized windows with aluminum or steel support bars.



New Home Windows

So where do you find energy efficient windows?

Any window manufacturer who sells energy efficient products that meets the recommended U-factor and Solar Heat Gain Coefficient in your climate. A reputation for service and strength that provides a warranty on the window should also be taken into consideration. Any ENERGY STAR® Windows program manufacturers that will have a permanent label on the product indicating their participation. An ENERGY STAR manufacturer is one who cares about the quality of their product and the product's energy efficiency.



Where do you go to buy an efficient window?
Start by doing research via the web and don’t be afraid to shop around for prices. Windows are complex devices due to windows are recommended by climate conditions. Climates where heating is significant have different product recommendations than climates where cooling is more vital. Know what kind of window is right for your climate and needs.

Visit distributors. Ask questions of the sales staff and let them tell you about the energy efficiency features of the products. Let them know what your price range is and have them show you only: 1) ENERGY STAR® label windows. 2) Have the NFRC label. 3) is a window that is right for your climate

Window with Energy Efficiency

Will new windows stop a draft?


 Drafty windows could have numerous causes. A wrongfully installed window is often the culprit. If the windows are improperly installed the imperfection can normally be corrected without removing or replacing the window. Caulking should prevent any air leakage. A good trick to see if the air is coming from the joint between the frame and the house or the joint between the sash and the frame is to hold a lighted candle in front of each joint. With the wind is blowing, slowly move it along the joint. If the flame flickers robustly or goes out, there is probably leak. Just make sure you don’t set the drapes or blinds on fire!

If the problems consist after caulking, you will need to replace the window. A properly installed energy efficient window will cease any air drafts from happing.
Will a new window eliminate condensation?

Condensation is a result of interior humidity and the variation of indoor and outside temperature. If you keep the humidity in your house at a low, the likelihood of occurring condensation is also low. If you keep your home at a high humidity, energy efficient windows will help reduce condensation. This is due to the high performance windows with low U-factors inside the glass surface temperatures are much closer to the room air temperature. Insulated "superwindows" with three or more layers will practically eliminate condensation on the interior surface of the glass.

Sources: Consumer Energy Information: EREC Fact Sheets, Energy-Efficient Windows, U.S. Department of Energy Window Shopping: Consumer Report, October 2000, pages 42-45. Energy Savers - Tips on Saving Energy and Money at Home, U.S. Department of Energy DOE/GO- 10097-431, September 1997.

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Comments (7) -

7/25/2010 7:15:58 PM #

Great scintific analysis of energy and air flow, I was looking for same...


Mosaic Mirrors United States |

12/10/2010 5:52:47 PM #

Usefull article can i mention this on my blog? Thanks

Faye Medieros United States |

12/13/2010 4:19:40 AM #

Go for it Faye!

racheal United States |

12/31/2010 8:27:52 AM #

I think these windows are stunning when they have a back view.  They can let in so much natural light, which will cause you to save on electricity.

Wharburtons United States |

1/26/2011 6:06:45 PM #

very nice article with great information and full tips.

solar heating India |

6/20/2011 6:30:17 PM #

Thank you for posting this informative article, It answers my question when I was young. Not all glasses are same purpose, Thanks for sharing this to us. Cheers!

pendant light fixtures United States |

8/16/2011 3:00:25 AM #

By windows, we can make our house more decent to look.

airsoft automatic guns United States |

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