Thermal Replacement Windows

Summary: While there are many reasons for replacing home windows, energy savings is fast dominating the home improvement scene. New windows (including the entire window frame) can eliminate "drafts," provide additional air spacing (insulation) between layers of glass panes and include reflective coverings to lessen solar intrusion and other forms of heat transfer. New windows can also add to home security (especially in hurricane-prone areas), leading to lower home insurance costs.

Energy Star TM appliances and energy efficient (e.g., hybrid) cars dominate the market these days. Many promise significant energy savings, which over their lifetime can result is energy savings that can approach the item's initial cost. Enter thermal replacement windows, which also offer some incredible energy savings, but, also improved home comfort as an added bonus. Many of these windows are rated Energy Star TM, as well.

Anyone who has lived in chilly climes knows that wintertime can bring a chill to a home. This is because windows from years ago were mostly single pane, and lacked a layer of insulating air sandwiched between two glass panes. Hence, when it turned cold outside, the glass pane became cold by contact and, in turn, the air inside, next to the window, got cold by contact. The cold air next to the windows would sink (cold air is heavier than warm air) leading to a feeling of "draftiness."

Often this led to condensation on the inside of windows, too, especially in bathrooms and kitchens. This in turn fostered damage to the wood casing, failure of window caulk and paint and the development of real air leaks.

Once air leaks developed, the so-called "drafty" windows became really drafty as air currents added to the intrusion of colder air.

Of course, the same flow of air from cold to warm locations occurred in summer, but the flow was directed out from the home. The only time one would notice a problem when condensation occurred on the outside of the window. Many would note that it was, "obviously very humid outside." As a result, people only became concerned with heat loss from windows in winter, when cold air came inside.

Today's energy efficient and low-maintenance windows take care of these issues and more and can lead to significant energy savings. Much like humans lose about 50% of body heat through the top of their head, windows could account for between about 15% and 35% of a home's energy loss. Your home may have a different percentage due to number and size of windows, where you live (geographically) and other variables.

Windows today are not rated by the typical insulation or R-value standard. Instead the newer U-rating accounts for heat loss by conductive heat transfer (contact) and emissivity (radiative and absorptive heat transfer). Lower U-factor ratings mean less overall heat loss. But glass now contains labeling (thanks to the National Fenestration Rating Council - NFRC) that highlights (1) U-factor ratings (lower is better); (2) Solar Heat Gain Coefficient or SHGC (lower is better); (3) Visible Transmittance (higher is better); (4) Air Leakage (lower is better); and (5) Condensation Resistance (higher is better). Each of these ratings has to be viewed from a geographical context. Lower SHGC's are more important in a southern climate, while lower U-factors are more important in colder regions. As you can see, rating windows is much more complicated than just a resistance to heat loss.

Replacing single-pane windows with double-pane Energy Star TM windows can result in large home heating/cooling savings. The U.S. Department of Energy estimates that for a 2,000 square foot, single story home, with 300 square feet of windows, savings could amount to between $300 and $500 annually in most parts of the country.

The U.S. Department of Energy at its Energy Star TM web site has posted a list of shopping tips for windows. Here are some of them:

* Look for the ENERGY STAR TM label.

• Check with local utilities to see what rebates or other financial incentives are available for energy efficient window replacement.

* Evaluate windows based on your climate zone.

• Look for whole-unit U-factors and SHGCs, rather than center-of-glass, or COG, U-factors and SHGCs. Whole-unit numbers more accurately reflect the energy performance of the entire product.

Most importantly, the DOE encourages people to have their windows installed by trained professionals and to be sure the windows are installed according to manufacturer's instructions. Otherwise, the window warranty may be voided.

http://www1.eere.energy.gov/consumer/tips/windows.html

http://www.energystar.gov/

http://www.energystar.gov/index.cfm?c=windows_doors.pr_anat_window

www.nfrc.org/documents/U-Factor.pdf

http://home.howstuffworks.com/home-improvement/energy-efficiency/insulate-windows.htm/printable