Windows and doors can account for as much as 25 percent of a home’s energy loss, but the right windows do a lot to bring that number down. In many climates, an investment in double- or even triple-pane windows pays you back with lower energy bills and a more comfortable home. More glass isn’t always better, though. Understanding how each type of window works will help you decide which one best meets your needs.
Single-Pane Windows: Affordable, but Inefficient
The standard window style until the 1960s, these windows consist of a single pane of glass in a frame. Because they’re so common, they’re easy to find in a wide range of styles and materials. If you’re upgrading or installing a window in a wall that can’t support the weight of double- or triple-pane windows, a single-pane window might be your only option.
Beyond this, the biggest benefit they offer is their low cost. Prices vary by window style, but on average, the purchase and installation cost of a single-pane window is usually not more than $200, while the cost for a double-pane model starts at around $350.
The downside is that they’re the least energy efficient. In a very mild climate, such as parts of California, Hawaii or the Southeast, your utility bills might already be so low that upgrading to double-pane windows won’t give you enough energy savings to justify the cost. Even in colder climates, single-pane windows aren’t always a home’s greatest efficiency weakness. If your home is drafty and lacks sufficient insulation, you’ll benefit more by solving those issues than by upgrading your windows.
If your single-pane windows have historic value or were artisan crafted for your home, you might prefer to keep them. In this case, you can optimize their efficiency by air sealing with caulk and weatherstripping, and by using storm windows and heavy drapes. In most climates, though, double-pane windows will keep you more comfortable and reward you with enough energy savings to recoup your investment.
Double-Pane Windows: A Happy Medium
In 1952, the Andersen Lumber Company, now the Andersen Corporation, introduced the Welded Insulated Glass window, the first double-pane window. By the late 1960s, these windows were in widespread use. Today they’re known as double-pane or double- glazed windows. You might also see the term insulated glass unit (IGU), which can refer to a double- or triple-pane window.
A double-pane window consists of a frame that holds two panes of glass separated either by air or by an inert noble gas with low thermal conductivity (usually krypton, argon, or xenon) to reduce the energy loss.
The cheapest models use ordinary air, which at least provides more insulation than a single pane. Inert gases are a better choice because they’re denser than air, so heat transfers through them more slowly. Each gas has pros and cons, but argon is the industry standard because it’s not only cheaper and more widely available than krypton, but it’s also a more efficient barrier in the 1/2-inch space inside most double-pane windows. In wider spaces, convection currents form and increase energy loss, rather than reduce it.
Krypton is denser than argon and a better insulator, but the improved performance doesn’t always justify the increase in cost. Even so, you might find it in narrow-profile double-pane windows with 3/8 inch or less between the panes. Xenon is highly effective, but also costly, so it’s usually reserved for cases where maximum energy efficiency is needed, such as in commercial buildings.
Built for efficiency, these windows are typically made with low-emissivity glass (low-e) glass, which is treated with a coating that reduces heat transfer. In a cold climate, upgrading from single- to double-pane windows can reduce your energy use by more than 20 percent. They’ll also keep you more comfortable, especially if you plan to sit anywhere near your windows.
Double-pane windows reduce noise, especially high-frequency noise such as the sound of lawn mowers and conversation. They’re less prone to condensation, meaning less risk of mold growth. Because they take more time to break through, these windows offer a little more security than single-pane models. They’re more common than triple-pane windows, so you’ll find a wider selection of styles. They can also increase your home’s market value. Even in an older home with walls made for single-pane windows, you might still be able to find a narrow, krypton-insulated double-pane window that fits.
The only real downside is the higher cost compared to single-pane models. While it might seem logical to upgrade a few windows at a time as your budget allows, you won’t see much, if any, energy savings until all your windows are upgraded. In a cold climate, gas-filled, low-e glass windows are preferable. If you’re in a milder climate and looking to save on costs, air-filled windows with low-e glass are a good compromise.
Triple-Pane Windows: Ideal for Cold Climates
A triple-pane window is similar to a double-pane window, but contains three panes of glass and two spaces filled with inert gas. The inner pane is completely isolated from the external ones. The spaces between the panes range from 1/4 to 3/8 inch, meaning krypton is more efficient in these models. The extra pane allows for another layer of low-e coating. These windows range in thickness from 7/8 inch to 1 3/4 inch, with thicker models generally being more effective.
Because their construction is more complex and requires more, higher-priced material, they cost around 10 to 20 percent more than double-pane models. They’re heavier and bulkier than double-pane windows, so you’ll also need a wall that’s strong and deep enough to accommodate them. Installation costs are often higher, too. This is true of sash, casement, and single- and double-hung windows.
Triple-pane are more likely to form condensation on the exterior pane, and while that doesn’t affect their efficiency, it can be annoying. They offer little improvement in noise reduction compared to double-pane windows.
Not every home needs triple-pane windows for optimal efficiency. The added expense of these windows means they’re only really worth the investment in cold climates where the temperatures stay far below freezing for weeks. If you’re in Maine, Minnesota, Wyoming, or another state in a Northern or Continental climate, the boost in efficiency and comfort from triple-pane windows is more noticeable.
In a mild climate, the increase in efficiency probably won’t lower your energy bills enough to justify the upfront cost. In a hot climate, you might see no improvement at all.
Which energy-efficient windows are right for you depends on your climate and your home’s construction. Single-pane windows are adequate in the mildest climates, but anywhere else, you’ll be better off with at least double-pane windows. If you’re optimizing your home for long, cold winters and you’re not on a tight budget, triple-pane windows might be your best option.