Windows can make or break a home’s thermal performance and energy efficiency. Windows with the wrong type of glass will cause rooms to overheat in summer, and in winter, those windows will leak heat like a sieve. This can drive up your heating and cooling costs year-round and make your home a less-than-comfortable place to be. 

If you’ve ever stood in front of an inefficient window during the winter (or the height of the summer) and felt the chilly (or hot) air passing directly through the glass, you know the importance of efficient windows. The right glass can help you make your windows work for you—between multi-pane options and energy-efficient coatings, a pro can help you decide on windows that perform at optimum efficiency throughout the year.

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Ready to learn more about your options? Keep reading!

Double And Triple Glazing: Which Glass is Best for Windows?

cross section of double- and triple- pane windowsSingle panes of glass in residential windows are pretty much a thing of the past. With energy efficiency being of primary concern for both builders and homeowners today, most windows now are at least double glazed—meaning each window comprises two panes of glass connected by a spacer, with the space in between filled with an insulating gas. These are referred to as Insulated Glass Units (IGUs).

IGUs can also be triple glazed—in other words, a third pane of glass is added to the window unit. Triple- glazed windows are costlier than double-glazed windows, and in most parts of the US, you won’t see a significant return on your investment either from selling your house or in savings on your utility bills.

If you live in an area that experiences extremely cold winters, however, talk to your window replacement contractor to see if triple-pane windows are a good choice for you.

The design of the spacer that connects the two (or three) panes of glass is also important to the overall performance of an IGU. In the past, metal was the primary material used in spacers. The conductivity of metal posed problems, however, and these types of spacers caused condensation and ice crystals.

To reduce the likelihood of trapped moisture between the panes, manufacturers now make spacers out of treated metal or structural foam combined with a desiccant that removes any moisture trapped within the space during the manufacturing process.

What’s the Best Window Glass Filling—Air or Inert Gas?

furnished breakfast room with windowsIGUs were once filled with air, but as the air warms and cools, its movement creates warm areas at the top of the window and cold areas at the bottom. Replacing the air with a less conductive gas reduces heat transfer, improving the performance of the glazing and lowering the unit’s U-factor, or rate of heat transfer.

Most IGUs manufactured today are filled with either argon or krypton gas. Both gasses are nontoxic, nonreactive, clear, and odorless.

Argon gas is more widely used because it’s more cost effective than krypton. If you opt for double-glazed windows filled with argon gas, the space between the two panes of glass will be approximately half an inch. 

Krypton gas takes up less space than argon gas, so it’s particularly useful for preventing triple-pane windows from becoming too deep to fit in a standard window frame. The optimum gap width for krypton gas is three-eighths of an inch, so if triple-glazed windows prove to be the best bet for your climate, your new windows will likely be insulated with krypton gas.

Low-E vs. Tempered Glass

Low-E coatings

A low-emittance (Low-E) coating is a thin layer of metal that is applied to one side of the glass during the glass manufacturing process. The coating is nearly invisible, and its purpose is to slow the rate at which heat transfers through the glass. US manufacturers always place the Low-E coating on the inner face of the glass pane to protect it from the elements and physical damage.

Different types of Low-E coatings have been designed to allow for high, moderate, or low solar heat gain. This innovation helps control the total amount of heat transferred through the panes and allows builders to tailor windows to the needs of the house by considering the overall climate and annual weather patterns. 

  • Higher solar-gain coatings allow more heat from the sun into a home or building, so they’re most commonly used in parts of the country with long, harsh winters.
  • Lower solar-gain coatings block approximately 75 percent of the sun’s heat, so they’re a popular option in warm climates.

Tempered glass

close up of broken tempered glass

Tempered glass, also called safety glass, is the smartest choice for windows and other glass structures in your home. Tempered glass is heated and then cooled very quickly during the manufacturing process; this rapid change in temperature makes it about four times stronger than untreated glass.

If tempered glass breaks, it’s designed to crumble into small, dull-edged pieces. Untreated glass will break under comparatively little force and will shatter into dangerous shards.

The International Residential Code dictates where tempered glass must be used in a house and where regular glass is acceptable, but keep in mind that there really aren’t any downsides to insisting on safety glass when it’s an option—even if it’s not required by code.

The Bottom Line

If you’re like most homeowners, when you think about replacing the windows in your house, your first consideration is probably frame material. Will you go with wood? What about low-maintenance vinyl? Should you opt for composite windows instead?

The actual glass installed in those frames may seem like an afterthought, or you may not realize that you have control over the type of glass to begin with. In fact, choosing the right type of glass for your windows can seem like a minor consideration in the overall scope of a home improvement project, but the decision can turn out to have major repercussions in both your home’s energy efficiency and comfort. 

When you work with a Best Pick window and door replacement professional, you’ll be getting the best of the best. Best Picks are licensed, insured, and highly rated by homeowners like you. Choosing the right window glass is an important decision, and a Best Pick pro won’t lead you astray—we guarantee it. Give one a call today!