Windows: Not a Pane-ful Choice

Windows are one of the largest investments you will make when building a new home. And that investment does not necessarily end once your builder installs the windows. Many windows end up costing the homeowner a substantial amount of money in long—term heating and cooling costs. Sun glare can also fade fine furniture, drapes and carpets.

Recent technology has made bay windows, French doors and panoramic picture windows a more affordable and energy-efficient option, though.

Many windows can now muffle the sound of your neighbor's lawnmower or the kids' game of Kick the Can outside your front door. Some windows can also filter out damaging sun rays that used to fade home furnishings; and others keep the outside temperature outside.

The type of window that will best fit your needs depends on a number of criteria—including the climate where you live and your personal style and budget.

One option that increases energy efficiency is a dual—pane window—or insulating glass. A dual-pane window uses two panes of glass to trap air, which acts as an insulator. Some manufacturers also inject a colorless gas like argon between the two panes to increase the insulation. Windows with three panes of glass and two air spaces are also available from some manufacturers.

Low—emissivity—or low-e—coating increases a window's insulating value even more. Low-e coating, which is applied directly onto the glass in one or more layers, also filters out damaging sunlight—particularly ultra-violet rays.

A window's energy efficiency is indicated with R-values and U-values. The U-value measures how much heat transfers through a window, so a lower U-value means a more efficient window.

The R-value measures how much heat flow a window resists. A higher R-value means a window insulates more effectively. Manufacturers often measure a window's "center of glass" R-value, which only considers the warmer center. A "total unit" R-value measures how much the entire piece of glass resists heat flow.

In 1989, the National Fenestration Rating Council (NFRC) formed to create a common system to measure the energy performance of windows and doors. Before the NFRC formed, every manufacturer rated the performance of its own products.

Participation in the NFRC is voluntary for manufacturers. Products that have been rated by the NFRC are noted with a label that indicates the window's U-value.

The NFRC, which is a non-profit coalition of private and public officials, also publishes a Certified Products Directory listing the energy ratings of the products they evaluate. The $10 directory is available from participating window and door manufacturers and from the NFRC in Silver Spring, MD.

Bob Wood, the marketing manager for Hurd Millwork Company, a Wisconsin-based window and door manufacturer, also stressed how important the proper installation of windows is to both energy efficiency and durability.

"If you have a reputable contractor or installed the window with the care it deserves, it should function properly," he said.

Some window manufacturers directly certify builders to install their products, while others have local distributors certify builders or contractors.

Once you have the knowledge, choosing a window is fun. Windows come in every shape for every imaginable space--circles, triangles, curved walls and with a built-in 90-degree angle to fit a corner. If the window you want is not part of a standard line, inquire about custom-made products.

"The most important thing to remember is that (you) will own that home for a long time," Wood said. "…The effort should be spent developing the envelope of the house. Maybe it will cost a little more, but that's where you're going to be living."

Proper care makes grand windows like these from Hurd Millwork Company an energy-efficient option. Hurd recommends that homeowners install different types of glass on different sides of the home to ensure top protection against northerly winds or late afternoon sun.
Photo courtesy of Hurd Millwork Company

Casement - A window with a hinged sash that cranks in and out.

Roundtop - A window in the shape of a half-circle.

Double-Hung - A window with two sashes that slide up and down.

Sidelight - A narrow fixed unit joined to one or more doors.

Transom - A window above another window or doors.

Argon-filled - A type of glass that delivers high energy efficiency. The sealed air space between panes is filled with argon— a colorless gas— which raises the insulating value.

CFM - Cubic feet per minute. A unit of measure for the leakage of air through a closed window.

Frame - The combination of head, jambs and sill.

Glazing - The process of applying or installing glass into a window or door sash. Also refers to the type of glass used in the process.

Head - Top of the frame.

Insulating Glass - A combination of two or more panes with a sealed air space between. Available for a variety of products and in a variety of glass thicknesses, types, sizes and assembly thicknesses.

Jamb - The part of a window that forms the side of the frame.

Low-E Glass - Low-emissivity glass has a transparent material on its surface, which acts as a thermal mirror. Low-e glass is used to increase a window's insulating value, to block heat flow and to reduce fading.

Pane - A framed sheet of glass within a window or door.

R-Value - A measure of how much a material resists heat transfer. The higher the R-value, the better the insulating effect and the lower the rate of heat flow.

Sash - An assembly of stiles (sides) and rails (top and bottom) made into a frame.

Sill - The bottom of the frame.

U-Value - A measure of how much energy a material conducts. The lower the U-value, the better the insulating effect.

Vent Unit - A window that opens. A fixed unit is a window that does not open.

Windowpane Divider - A bar that divides (or appears to divide) glass into separate panes. Also called a muntin or grille.

Courtesy of Pella Corporation