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How to Choose Energy-Efficient Windows for Your Home

Devon Thorsby

About 30% of a home's heating energy is lost through the windows, according to the U.S. Department of Energy. But with the right windows and long-term care, you can cut back on air leakage, reduce unnecessary heating and cooling and lower your utility bills.

Window replacements are pricey, however, costing about $650 per window on average, according to HomeAdvisor. The cost can range from $300 to $1,000 per window depending on material, size and features, and those that are energy-efficient tend to be more expensive. While you will likely see reduced utility bills with these, don't expect to recoup the value quickly. However, new windows can increase your quality of life by keeping rooms the right temperature, reducing outside noise and improving curb appeal.

[Read: 5 Temporary Fixes When You Need a Major Winter Home Repair]

Here are the details to consider when you begin shopping for energy-efficient windows:

-- Rating.

-- Window type.

-- Frame.

-- Panes of glass.

-- Coating.

-- Spacers and filling.

Rating

When shopping for windows, look for certified Energy Star products or those with an optimal rating from the National Fenestration Rating Council, which has a voluntary program for testing and certifying windows, doors and skylights. NFRC ratings are incorporated into Energy Star certifications; Energy Star is a program run by the U.S. Environmental Protection Agency.

With NFRC ratings, the lower the number, the more energy-efficient the product. The key ratings are:

-- U-factor. The amount of non-solar heat that can transfer from outside to inside.

-- Solar heat gain coefficient. The amount of solar radiation that can transfer from outside to inside.

-- Air leakage. The amount of air that flows through the window, measured by cubic feet per minute of air transfer.

-- Visible transmittance. The amount of visible light transmitted from outside to inside.

"These values vary depending on where you are, and homeowners should be aware of the requirements in their particular climate zone," Troy Rubenzer, product manager for window replacement company Renewal by Andersen, wrote in an email. Energy Star has four established climate zones throughout the U.S., based on the seasonal temperature and hours of sunlight.

Fortunately, you won't be hard-pressed to find Energy Star-certified windows when you start shopping; it's just a matter of selecting the right window and features for your home. "It's almost impossible to not find an Energy Star-rated window. It's counterintuitive (for manufacturers) to not make that," says Jeff Ludy, founder and owner of Houston Window Experts. Just like with household appliances that carry the Energy Star certification, the Energy Star logo will be prominent in any product description that meets requirements, along with the individual NFRC ratings.

Window Type

When choosing a type of window for your home, consider whether it is more or less likely to leak air. Here are the most common types of windows:

-- Single- or double-hung. These windows have an upper and lower sash, or movable portion of the window. A single-hung window can only be opened by sliding the bottom sash up, while both sashes can move up or down.

-- Sliding. A window with sashes that open by sliding horizontally.

-- Casement. A hinged window that opens from the side.

-- Awning. A hinged window that opens from the bottom.

-- Hopper. A hinged window that opens from the top.

-- Fixed. A window that does not open. These are rare in residential homes, as building code requires the ability to open windows for air or as a means of egress in case of a fire.

The double-hung window is one of the most popular types of windows on houses today. But according to the Department of Energy, it's also more likely to leak air than a casement, awning or hopper window. Sliding windows also have higher leakage rates, as the Department of Energy notes in its breakdown of window types.

However, hinged windows such as casement, awning and hopper windows may not offer the look or functionality you want. They require more space around the window to allow them to open inward and may not open wide enough to welcome a breeze.

Frame

The material of the frame you choose is an important consideration when you're looking to insulate your windows.

Vinyl and fiberglass offer substantial energy efficiency as long as they are properly insulated. Wood or composite frames can also insulate well, but their performance is not as high as fiberglass or vinyl that has insulation included. Wood frames also require more maintenance. Metal frames have the lowest performance quality regarding energy efficiency.

Panes of Glass

If you live in an old house with original windows, there's a good chance they have a single pane of glass, which does not effectively stop outdoor temperatures from affecting your inside climate control. Windows today are often double- or triple-paned, with space in between, which cuts down on the loss of thermal energy.

Coating

Energy Star-rated windows today have three coats of low-emissivity, or low-e, glazing. This coating reduces the amount of sunlight that comes through the windows. Ludy points out that in some cases, a homeowner with a house that receives little direct sunlight might want fewer coats of low-e glazing to keep the house from feeling even darker.

Spacers and Filling

Between your panes of glass, there are spacers to help keep the glass in place, and they also provide an additional level of protection to keep windows airtight and moisture-resistant. Spacers come in different shapes and materials, such as stainless steel, aluminum and silicone foam, and with sealants to keep them effective.

You may also have the space between panes of glass filled with gas to cut down on heat transfer. The Department of Energy notes that krypton and argon are the two most common gases used -- krypton for space around one-quarter inch, and argon for wider spaces.

[Read: 8 Ways to Upgrade Your Front Porch.]

In addition to the window itself, consider things that can keep your windows energy-efficient:

-- Proper installation.

-- Warranty.

-- Weatherstripping and caulk.

-- Window treatments.

Proper Installation

Not only do you need to find the right energy-efficient windows for your house, but you need an installer who is going to do the job right. As Ludy says: "A great window with a bad installer is a bad window."

Be wary of installers that are willing to make an estimate without visiting your property, taking measurements and learning about the structure of your home, he says. Wall thickness and the exterior material of your house play a role in what type of window fits best.

Like with any contractor, you should have multiple service providers come to your house and provide an estimate. While price will certainly play a role in your final decision, also factor in whether the product offers the level of energy efficiency you want and meets other needs.

Warranty

If you're offered a lifetime warranty on your new windows, be sure to read the fine print. Rubenzer says some warranties only cover the glass or frame, or the warranty won't transfer to the new owner if you sell the house.

The company you choose should also have a solid history of doing business. "A lifetime warranty does you no good if the company it comes from is here today and gone tomorrow," Rubenzer says.

[See: Don't Call the Handyman: 9 Quick Fixes You Can Do Yourself.]

Weatherstripping and Caulk

Over time, your house settles, and windows and doors may not remain as airtight as they were upon installation. Check annually around your windows for any leaks that might be letting cool air in during winter and out in the summer.

On the exterior of the window frame, you can use caulk to seal edges where air can get in. If air is leaking between the window and frame, you can use weatherstripping, which is a padded strip with adhesive on one side, to provide more insulation.

Window Treatments

Blinds, covers and curtains aren't just for privacy or aesthetics. They can also offer additional insulation to reduce heating or cooling loss through windows. If a room has a tendency to get hot due to direct sunlight on summer afternoons, close the blinds or draw the curtains to avoid having to crank the air conditioning higher.

In the winter, be sure to open blinds and curtains when the sun is out to help reduce the amount of work your furnace has to do.

For more information on energy-efficient windows, the Department of Energy has an in-depth guide that breaks down all the details of replacing your windows.



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