Go Green > A Clear Case for Energy Efficiency

A fresh summer breeze is welcome in our homes this time of year, but by late fall, we’re shutting the windows to keep the heat in and the cold out. Windows provide fresh air, daylight and access to views, but they also are thermal holes that can be either friend or foe when it comes to the energy efficiency of your home.

It is estimated that windows contribute as much as 25 percent of a home’s heat loss, according to Green Remodeling by David Johnston and Kim Master. The cost of replacing windows is high, but you’ll want to measure that against the expected reduction of your heating and cooling costs as well as the environmental bonus of reducing your carbon footprint.

If you are contemplating replacement windows, the first step is evaluating whether additional caulking and proper insulation are enough of a warm winter jacket for your home. “Whenever anyone calls regarding windows, I always ask what other work can be done on the home first to reduce infiltration because windows are so expensive that the payback takes a long time,” says Andy Gray, weatherization program manager at the state’s Office of Energy and Planning in Concord. “For example, adding insulation to the walls and attic can substantially reduce heat loss.”

Home Design and Replacement Windows

As you consider replacing windows, it pays to reevaluate the windows’ location in your home. Do you really want to replace a window on the colder north side of your home, or would it be better to close up the hole? Can you add a window on the south or southwest side to increase daylight and solar gain?

Look closely at your home’s design and overall style—outside and in—so new windows maintain the home’s harmony.

Some windows feature “divided lights” or individual panels of glass that form patterns. If you’re replacing this type of window, consider a modern, simulated divided-light window that has a grille bonded to the outside and a wood grille on the inside.

Philip Kendrick, a Dover-based architect, recommends a wood-sash replacement window with the same glass pattern as others in the home. “A vinyl or aluminum-clad wood-sash window is stronger for its size than other materials, like a solid vinyl window,” he says.

“If the home is a reproduction or is intended to look like a certain period, it’s more difficult to keep it right,” says Kendrick. With a period home, he encourages homeowners to maintain the existing window size. For example, typically smaller windows are used on the second floor of historic houses, yet this usually will not meet the today’s requirements for square footage or safety codes. “What I do is use a casement window with a grille pattern to represent a double-hung that meets the code if there is more than one window in the room,” he says.

For properties or houses with distinct historic attributes, Kendrick recommends trying to retain as many existing windows as possible. “Have them scraped, primed, repainted, restore the glazing and add new weather-striping,” he says. “You can add a storm panel of glass or Lexan® in a frame that sets in the window opening either inside or out. This will bring it close to the energy standards of a new window.”

Shopping for Windows

After you understand your design criteria, it’s time to place your order. Find a good salesperson at a reputable company who will walk you through the process or consult with your contractor. Ask about glass and frame warranties as well as installation specials. New windows may be one of two types: a new construction window that is fully framed and requires removing the existing frame before the new window is installed from the outside, or a true replacement window that uses the existing frame and is installed from the inside.

Gray recommends looking for Energy Star-labeled windows. Energy Star is a joint program of the Environmental Protection Agency and the Department of Energy that sets strict guidelines for energy-efficient products and practices. An Energy Star-rated window makes use of quality frame materials, double panes, spacers to keep the panes the correct distance apart, special glass coatings, and sometimes, a gas fill between the two panes.

Eric Kizirian of Brock’s, a building materials retailer in Rochester, says that each window company has its own name for energy-efficient windows; for example, Andersen™ calls its windows These wood, double-hung windows (this page, top and bottom) by Jeld-Wen were chosen by TMS Architects for their quality, energy efficiency and cost. “The wood is pressure-treated with a water-based, eco-friendly preservative to resist rot and insect damage,” says John Merkle of TMS. “Jeld-Wen also has a long history of recycling and being environmentally conscious.” High Performance™ and includes low- E coating with an argon-gas fill between the two panes. “The argon gas adds density to the space between the two panes of glass, helping to stop the penetration of heat or cold,” says Kizirian.

“Low-E glass—for ‘low emissivity’— is a silver film manufactured into the glass itself,” he says. “It helps to reflect ultraviolet rays and radiant heat. If you hold your hand to glass in the winter, you can feel the cold; but low-E treated glass helps to keep the cold out and the heat in, and vice versa in the summer. It does not affect the visible light transmission of the window.”

The space between the panes is also important. More insulation from heat loss is gained with greater space, usually between one-half and seven-eighths of an inch. All windows carry a “U-value” rating that measures the flow of heat through the glass, given the difference in temperature on either side. The lower the U-value, the less heat loss. “A quality residential market window, on average, would carry a .31 U-value,” says Kizirian.

Professional Installation Increases Energy Efficiency

“Even the best window won’t perform well without proper installation,” says Gray. “It should be square in the opening, and the area between the frame and the opening should be filled with non- or low-expanding spray foam. This seals the surrounding space completely without squeezing the window frame and making it hard to open.”

If your home was built before 1978, be aware of any lead paint that still may be present. “There’s a whole setup to do so as not to spread lead dust,” says Gray. “It’s not difficult to do; the key words are ‘work wet and clean.’”

Replacing windows are expensive, yet they generally last for between fifteen and twenty years, and the work can be done over time. “The prices are pretty stable and may increase from 1 percent to 2 percent annually,” says Kizirian. “My parents have been doing one a year for the last three years.”