Letting (Just) the Light In
Open up to new technology
Windows let in light, air, and a view of the world. But inefficient windows–as well as inefficient skylights and entry doors–are like holes in your walls and roof. They let out too much heat in the winter and let in too much heat in the summer. And that boosts your energy bill.
The good news is that window technology has made huge strides in the past couple of decades. Today’s energy-efficient windows can be twice as efficient as those sold only ten years ago. They usually have two panes of glass separated by an air gap that helps keep heat from moving between indoors and outdoors. They also block sound, so you won’t be as bothered by Bowser barking next door. Additional features include energy-efficient window frames and heat-blocking coatings for glass.
If you add it all up, today’s energy-efficient windows can reduce energy costs by as much as 15%, depending on where you live. For the average household, that means savings of between $130 and $460 a year for replacing single-paned windows or between $30 and $110 a year for replacing old double-paned ones.
- Caulk first. Be sure to plug leaks and reduce drafts. Even the best window can’t do you much good if you have holes in your house.
- Consider storm windows or shades. Storm windows can be a good, less-expensive alternative to new windows. Also, insulating curtains or shades can reduce drafts.
- Add skylights? A skylight can brighten a dark room and reduce the need for electric lights. Tubular skylights are great for small rooms, bathrooms, and hallways. They’re easier to install, less expensive, and more energy efficient than regular skylights.
- Keep the doors. Fiberglass and insulated steel entry doors are much more energy efficient than solid wood doors. But replacing your door is expensive, and it won’t cut your energy bill by much. It’s more cost effective to block drafts with weather stripping and door sweeps. Adding a storm door is another low-cost way to boost an entry door’s efficiency.
When shopping, look for
- Energy-efficient window frames. Those made of wood are energy efficient but can be expensive, and the exteriors need frequent repainting. Many now come with a protective covering of metal on the outside to make them more weather resistant. Vinyl frames are as energy efficient as wood and much less expensive, but they can expand and contract in hot or cold weather, compromising the window’s performance. Some manufacturers blend vinyl with other materials to make them more stable. The biggest downside is that vinyl manufacturing and incineration creates dioxin, a highly carcinogenic chemical and so its use should really be avoided. Fiberglass frames are also energy efficient and don’t expand or contract, but are more expensive than vinyl. Aluminum frames are inexpensive but the least energy efficient. It’s best not to use them except in the mildest of climates.
- Coated glass. Low-emissivity or “low-e” coatings are a microscopically thin, transparent coating on the glass of energy-efficient windows. Standard low-e coatings help keep the room’s heat inside, making the room feel more comfortable when it’s cold outside. In cold climates, low-e windows can cut heating costs by more than 30% compared with single-pane windows. Other kinds of low-e coatings keep heat in and also block much of the sun’s heat from entering through the windows. This feature can reduce cooling costs by nearly 40% in a hot climate, but is less desirable in cold locations.
- Gases in the gap? In some window products, the gap between the panes of glass is filled with a colorless gas, such as argon or krypton, that’s an even better insulator than air. It’s not clear whether these gas-filled windows are worth the extra money, since there’s no way to tell if the gas leaks out over time.
- Energy Star label. Windows, skylights, and exterior doors with an Energy Star label are certified to meet energy-efficiency guidelines set by the U.S. Department of Energy. You can browse the Energy Star website to see how well products will work in your particular climate zone. It’s also worth checking out the NFRC (National Fenestration Rating Council) labels, which offer even more detailed comparisons.
- New windows are expensive, so replacing single-pane windows with energy-efficient windows won’t necessarily be cost effective based on energy savings alone unless you plan to live in your home for years to come. However, there are other reasons to replace your windows including making your home quieter and more comfortable. If you’ve done all the easier, less-expensive tune-ups and still have high energy bills, replacing the windows might be the next step.
- If you decide to replace your windows, the least expensive option is installing a new window designed to fit the old window frame. This is commonly done when replacing double-hung windows. But if the frame is in poor condition, you’ll need a new window and frame.
- If you’re remodeling or building a new home, be thoughtful about the size, number and placement of windows and skylights. In hot climates, too much glass on the west and east sides and overhead can drive your air conditioning bills through the roof. In cold climates, glass on the building’s colder north side will make your heater work harder. A good architect can help you design your home properly.
- What to do with your old windows, exterior doors and skylights? Call your local building materials reuse store (aka salvage yard or junkyard) to see if they’ll take them off your hands. If your windows or doors are vintage or have unique architectural features, they’ll be more likely to want them–or you may be able to sell them. Or get creative: old doors can be used as desktops, and old windows can be used as cabinet doors (don’t use them on lower cabinets where there’s a danger that someone could break the glass with their foot or knee).
No more avoiding sitting next to the window or under a skylight because it’s too cold in the winter or too hot in the summer. Energy-efficient windows, skylights, and doors make your home more comfortable. Energy-efficient windows are also less likely to be fogged with condensation on winter mornings. Special coatings on windows and skylights block UV rays, protecting fabrics, wood, and artwork from fading.
…to the Earth
Energy-efficient windows, skylights, and entry doors reduce fossil-fuel use and greenhouse-gas emissions.
- Overheating. In hot climates, large clear skylights may introduce too much heat. Choose skylights with special coatings designed to reduce heat gain, or install small tubular skylights that bring in daylight without as much heat.
- Messing with lead paint. Installing new windows and doors often involves scraping and sanding old paint around the window opening. Take precautions when dealing with any lead-based paint.
- Blocking the winter sun. It’s usually not a good idea to plant evergreen trees on the south side of your house. You’ll get year-round shading and won’t be able to take advantage of the sun’s warmth in the winter. Deciduous trees and vines, on the other hand, will shade you in the summer and bring more heat and light into your home in the fall, when they shed their leaves. (Plants are also champs at absorbing CO2.)
- Check with your local utility company–some offer rebates to homeowners who install energy-efficient windows and exterior doors.
- Choosing windows and skylights can be intimidating. Not only do you have to think about style, materials, and cost, there’s also a wide range of performance issues to consider. A new window or skylight will affect a home’s comfort and energy costs for many decades so it’s important to choose well. Unfortunately, not all architects, builders, or window salespeople have a good grasp of energy-efficient window technology and the pros and cons of various options. If you can’t take the time to become a window expert, at least spend some time tracking down a knowledgeable window professional. Ask local green building organizations or green builders for recommendations.
- If the window frame is in good condition, you can buy replacement windows designed to fit within the existing frame. You can install them yourself if you’re handy, or you can have them professionally installed by a builder or window dealer. If the window frame is damaged or rotting, or if you want to change the shape or size of the window, you’ll need to buy a full-frame window that includes new sashes (the part of the window that includes the glass and the framing pieces directly attached to the glass), the frame (the fixed perimeter that the sashes are set into), and the casing (the molding around the window’s interior and exterior that covers the space between the wall and window frame). Full-frame replacement should be done by a window professional unless you are experienced with building construction.
- Tubular skylights are much easier to install than larger conventional skylights. A professional skylight installer, builder, or handy DIYer can put in a tubular skylight in a few hours.
- For general advice on what questions to ask contractors and other tradespeople, see our “What to Ask Your Contractor” article.
- If you decide you want to study the detailed information on windows, skylights, and entry doors provided by the NFRC(National Fenestration Rating Council), you may encounter some unfamiliar terms. Here’s a decoder:
- Air leakage tells you how much air will pass through the entire window assembly. A lower number means less air leakage. Manufacturers of lower-quality windows may not include an air leakage number.
- Condensation resistance is a measure of how well the window will resist the formation of condensation on the inside of the glass. A higher number is better.
- Solar heat gain coefficient (SHGC) indicates how much of the sun’s heat will enter through a window. The higher the number, the more heat will enter your home. An SHGC of 0.40, for example, means that 40% of the sun’s heat gets through the window.
- U-factor tells you the window’s resistance to heat flow. The lower the U-factor, the better the window is at keeping warmth inside your home. (Those low-e coatings mentioned above help lower a window’s U-factor.)
- Visible transmittance tells you how much light (as opposed to heat) the window lets in. Lower numbers mean more daylight is blocked.