Down Economy Encourages Window Shopping
If you're thinking about replacing your windows, now is a great time to do just that. As part of the economic stimulus plan, the Federal government is offering a 30% tax credit up to $1500 toward more energy efficient windows. You can visit Energy Star's website at http://www.energystar.gov and click on the Tax Credits for Energy Efficiency tab for the details on the program. With energy prices on the rise, replacing your windows is one way to keep your energy costs down. But before you sign on the dotted line, here are some things you should consider.
By the numbers
The two numbers that you will be most interested in while window shopping are the U-factor and the Solar Heat Gain Coefficient (SHGC). The U-factor is a rating given to a window based on how much heat loss it allows. A low U-factor means that a window allows less heat to escape. Beware of misleading advertising that touts “center of glass” U-factor. The center of the glass is the warmest part of the window. The Federal government requires a .30 whole unit U-factor to qualify for the tax credit.
The Solar Heat Gain Coefficient (SHGC) is a number assigned to a window that tells you how much heat from the sun that window allows into your home. SHGC numbers range from 0 to 1, and the lower the number, the less heat will enter your home. So, in hot climates a low SGHC is desirable, while in cold climates a higher SGHC is desirable. A .30 SHGC is required to qualify for the
Federal tax credit. Since we live in a cold climate, you may want to consider a higher SGHC window on the south elevation of your home. Even though it won't qualify for the tax credit, it will help reduce your winter heating bills.
Another number of interest is the Design Pressure Rating (DP rating). The DP rating refers to a window's structural loading performance and describes it's ability to withstand uniform loads caused by winds. The higher the DP rating, the stronger the window is structurally. The DP rating has no bearing on the Federal tax credit but knowing and understanding this number will help you compare the durability of a window in the high winds we experience from time to time in Northern Colorado.
Frame options
Much has changed in the way of residential window frame materials and much has remained the same. Wood has long been a traditional window frame material and is still widely available today. Wood offers character and beauty and is a natural insulator. You can paint it or stain it to accent any decor. Contemporary wood windows have exterior claddings for low maintenance living. Cladding materials include vinyl, roll form aluminum and extruded aluminum. Extruded aluminum is the most durable. It provides a solid substrate for a long lasting factory finish . With proper maintenance aluminum clad wood windows can last more than 30 years.
Fiberglass is the frame material of the future even though it's been in use for more than a decade. Fiberglass offers nearly the same expansion/contraction rate as glass which reduces the possibility of seal failures in the insulated glass unit (IGU). It also provides a stable base for durable factory finishes and is paintable if you ever want to change your window color. If properly maintained, fiberglass windows should equal or exceed the life of aluminum clad wood windows. Depending on options chosen, fiberglass windows are available at a small premium to vinyl windows.
Vinyl as a window frame material has also been around for a number of years. Vinyl is comparatively low in cost, however vinyl is only available in light colors and has a high rate of expansion and contraction as compared to glass. The lifespan of a vinyl window will be much less than wood or fiberglass.
You want glass with that?
A window offers us a view to the outside world, natural light into our interior living space and an opportunity for ventilation. Since none of us wants to live in a cave, we sacrifice the insulation value of a wall when we cut a hole to install a window. Since glass accounts for the largest area of a window, it has a large impact on the insulating value of the window.
The big gains in window technology over the past 30 years have been in glass coatings. Low-e stands for low emissivity. Emissivity is inversely related to reflectivity. In other words, if there is a heat source inside (or outside) your house, the low-e coating bounces the heat back away from the glass. There are two different types of low-e glass; hard coat and soft coat. Soft coat low-e is the better insulator and reflects more heat. If you're interested in a higher SHGC, hard coat is the way to go.
Another way to improve the U-factor of the IGU is to add an inert gas like argon, krypton or xenon to the air space. Argon is the most popular since it's the most affordable of the available choices. Inert gas reduces the rate of heat transfer greater than ambient air that is trapped in the air space during the construction of a standard IGU.
There are many other features worth considering that will affect window design and performance. Triple glazing, sound transmission class, decorative grids, and glass tinting options are only a few. Your best bet is to contact your friendly neighborhood window professional to discuss all the possibilities.
Jim Webster, Certified Graduate Associate (CGA), Certified Aging in Place Specialist (CAPS), Certified Green Professional (CGP) and Friendly Neighborhood Window Professional (FNWP) is General Manager of SolarGlass Window & Door of Northern Colorado. He has been a member of the HBA of Northern Colorado since 1996. He is also a member and past chair of National Association of Home Builders - Remodelers (NAHBR). He can be contacted at jwebster@solarglass.com or by calling 970.224.1930.