Part four of a series

Winter's approach means it's time for homeowners to batten down the hatches. Otherwise, hard-earned money can seep out of leaky windows and doors.

Bracing for Winter

Installation of tight-fitting barriers to air are two basic steps to locking in savings.

Keep up with the weekly multimedia series on how to cut home heating costs...

"You probably lose about a third of your energy through windows and doors," said Paul Fisette, director of the Building Materials and Wood Technology program at UMass-Amherst.

Whether shopping for a home or pondering a remodeling job, consumers can get dreamy about window views or mesmerized by prices -- even standard-sized windows can cost hundreds of dollars each.

"Payback is going to take you a long time . . . because you're going to spend a lot of money," said Jim Benney, executive director of the National Fenestration Rating Council, based in Silver Spring, Md.

But consumers need to look at some other numbers before they spend money. Things like U factor, Solar Heat Gain Coefficient, Visible Transmittance, Air Leakage and Condensation Resistance.

To help understand these terms, to learn how they affect energy efficiency and to sort out which are the best windows and doors for their homes, consumers can turn to the Energy Star program and the National Fenestration Rating Council.

The U.S. Department of Energy and the federal Environmental Protection Agency developed Energy Star to designate products meeting certain energy-performance criteria. Because window performance varies by climate, product recommendations are given for four climate zones.

To be designated an Energy Star product, a product must be certified and labeled by the nonprofit National Fenestration Rating Council.

The NFRC provides certified energy-efficiency data that allows for product comparisons. Energy ratings appear on NFRC labels attached to windows and doors.

"You get an apples-to-apples comparison," Fisette said.

Benney said the NFRC goes to great lengths to ensure that windows, skylights and doors measure up to manufacturers' claims.

"When consumers see an NFRC label, they know that they're getting what it says," Benney said.

A window's energy efficiency is the inverse of insulation.

Insulation is rated by an R, or resistance to flow, value. The higher the number, the better it insulates.

Windows are rated by a U, or flow, value. The lower the number, the lower the amount of heat loss through a window.

In New England, Fisette recommends windows that have a U value no higher than .33.

"U values are very important, but so is air leakage," Fisette said.

Leakage is expressed in cubic feet of air passing through a square foot of window area. Windows with a leakage rating of .30 or less are recommended.

But some experts say that more important than leakage is the solar coefficient. Expressed as a number between 0 and 1, the lower the coefficient, the lower the amount of heat gained from the sun.

How much solar heat you want depends on where you live and whether your house can absorb heat without the indoor temperature getting uncomfortable or triggering air conditioning.

"If people go with high-gain [windows], they're not going to be very happy in the summer if their house isn't oriented properly," said Kip Rhoades, program manager of the Efficient Windows Collaborative, an offshoot of the Alliance to Save Energy, of Washington, D.C.

In addition, visual transmittance indicates how much visible light moves through a window. Varying between 0 and 1, the higher the VT, the more light is transmitted.

Clear glass absorbs heat and dumps it outdoors. A low-emissivity (low-e) coating on the glass is a key factor because the coating reflects heat back into the room during the winter months, reducing heat loss by 25 percent to 50 percent, according to the alliance. Low-e windows are almost a standard, particularly in the Northeast.

And windows should be able to resist condensation, which can damage the frame material. Resistance is expressed as a number between 1 and 100 -- the higher the number, the better the window is able to resist condensation.

In the United States, almost half of the homes have single-pane windows, but experts recommend that homeowners install double-pane windows because they are cost-efficient.

"Old single-pane windows, they're not much of a barrier," said Ronnie Kweller, of the energy alliance.

In double-pane windows, there is a gap between the two sheets of glass and it's typically filled with argon, a gas that increases energy efficiency.

"The glass itself doesn't do much, it's the low-e coating and the argon gas," said Michael Southworth, manager of Humphrey's-Marvin Showcase in Middletown. "

The experts also recommend that consumers stay away from all-aluminum windows, preferring wood clad in vinyl or all-vinyl products. Frames should have a thermal break to impede heat loss.

When locked, casement windows seal tighter than double-hung windows, so they're more efficient.

But energy efficiency can be undermined by poor installation. "The window you're installing might be great, but the contractor might not install it right," said Benney, of the NFRC.

Doors tend to be less problematic than windows.

"The most important thing on a door is that it has a seal on the bottom that really does seal," Fisette said.

For people who don't want the expense of replacing their old doors and windows, sealing up air leaks with caulking and weather stripping is the way to go.

The DOE and the energy alliance note that plugging air leaks with caulking, sealing or weather stripping can save 10 percent or more on your energy bill.

"Less than half of American homeowners take steps to winterize their homes," by caulking, said Shawn Williams, the general manager of General Electric's sealant division.

If applied properly, silicone caulk will last the life of a window or door, he said. It doesn't shrink or crack.

Air leaks can be found by placing a huge fan in an outside doorway and sucking air out of the house. Drafts and other leaks can be felt easily.

Or, on a windy day, hold a lit candle next to windows, doors and electrical outlets. If the smoke travels horizontally, there's an air leak and it should be sealed.

In the end, tighter, well-maintained energy-efficient windows and doors will mean more to homeowners than money.

"It's not just a dollar return," said Benney, of the NFRC. "You're getting a nicer home to live in."

For more information on energy-efficient windows and doors, visit the following Web sites.

www.nfrc.org

www.efficientwindows.org

www.ase.org

www.energystar.gov

http://hes.lbl.gov/

www.eere.energy.gov

Paul Grimaldi covers retailing and consumer behavior. E-mail him at pgrimald [at] projo.com