The FAQs on Gas-Filled Windows

The term is appearing more often in descriptions of window products: argon gas, which fills the thermal break between glazing units. Or maybe it’s krypton gas that’s specified. Is there a difference? Does it offer an advantage? Is there a concern if this gas escapes? Many homeowners ask these questions. Some know the answers to these questions and expect their contractor to be at least as knowledgeable as they are. Here are the frequently asked questions (and their answers) to help educate yourself on these energy-efficient products.

What Gases are Used in Windows?
Argon is the gas most often used between panes in a double- or triple-glazed window. Like the others mentioned, it is colorless and odorless, says Bill Lingnell, head of Lingnell Consulting Services in Rockwall, Texas, an independent consultant who works with the Insulating Glass Manufacturers Alliance (IGMA). Argon is denser than the atmosphere, providing more thermal efficiency than having air between the panes, he explains.

Krypton gas is denser than argon, and xenon gas is denser than krypton, providing somewhat more thermal efficiency. Some manufacturers also may offer a mixture of two gases. But the incremental benefit of these higher densities is hard to justify in their cost, says Carroll Bogard, manager of Trade Segment Marketing for Pella Windows in Pella, Iowa. “Dollar for dollar, argon gas does the best job,” he says.

What Benefits Does the Gas Offer?
Added energy efficiency is the key benefit, Bogard says. The gas acts as an added insulator, working in both summer and winter to keep interiors insulated from outside temperatures. Typically, gas infusion is provided in conjunction with applying a low-emissivity (low-E) coating film to the glass panes, he notes.

The other key advantage is the added comfort that can be achieved for the home, Bogard says. The low-E coating and gas help keep the interior pane of glass closer to the temperatures of the interior air, minimizing the creation of air currents as the different temperatures contact. This helps reduce drafts and winter “cold spots.” He stresses that proper installation is “absolutely essential” to achieve this benefit, however, and contractors should be trained in proper installation techniques and/or use experienced installers.

Is the Gas Harmful if it Leaks?
No. The gases are inert (nonreactive) and occur naturally in the Earth’s atmosphere. Argon, the most common, comprises about 2 percent of the air we breathe, Lingnell notes. “It can’t hurt you or make you ill if it leaks,” he says.

How Do I Know it’s There?
Scientific detectors can verify the presence of gas, Lingnell says, but homeowners usually rely on their contractor and the manufacturers’ reputation.

What if it Leaks Over Time?
“Reputable companies have their windows certified against seal failures to ensure that won’t happen,” Lingnell says. Members of IGMA use standards created by ASTM International to certify against leakage. “The major window companies certify their windows, but many smaller ones do not,” he warns. “Contractors should look for certification to reassure their customers.”

Even if a small amount of gas does leak, it won’t hurt the window’s performance, notes John Swanson, editor of Window & Door magazine, which is published by the National Glass Association (NGA). “Studies show that even if 80 percent of the gas remains, it will still maintain its effectiveness,” he says. “So, even if 1 percent was leaking out per year, the window would still be effective in 20 years.” Should the window lose all of its gas, Lingnell adds, it might be noticeable due to condensation on the windowpane or fog inside the pane.

How Much Does it Cost?
Determining the incremental price of gas filling and its resulting payback or return on investment depends on many variables, including the size of the window, materials used, glazing options, location and climate conditions, Bogard explains. Some companies provide an upgrade package that includes both low-E coating and argon gas, Swanson says. The value of the added comfort that can be gained by eliminated drafts can’t be summed up in a strict payback cost either, he adds.

Is Gas Filling a Popular Option Today?
“It’s a technology that has been around a long time, and it’s become popular because energy codes are more stringent,” Swanson says. Most codes are designed as performance standards, meaning they set a standard that must be met and allow the manufacturer to meet it, however works best. Many are finding the best way to do that is with gas-filled windows. “Consumers are becoming more educated about this option and are asking about it,” he adds.

To help consumers understand the features and benefits of energy-efficient windows, Pella provides brochures that include information about argon gas-filled windows, which are available at Lowe’s stores. The brochure explains that the windows help meet Energy Star ratings, Bogard says. It also explains how to apply for federal energy tax credits, which provide rebates on energy-efficient products such as Energy Star-qualified argon gas-filled windows, he adds.

It’s also not a technology that is about to be replaced, Lingnell notes. “A new generation of windows is pretty far from becoming commonplace,” he says. “It’s not like computers, where you may be obsolete when you walk out of the store. There are technologies being developed, but as of now, they’re not affordable.”