One, Two or Three — How Many Window Panes Do You Need?

Seattle has a rainy reputation. And it’s well-deserved. It rains 152 times a year on average¹ — about three days a week. All that rain is a result of the mild, temperate climate. Extreme temps are rare. It’s never too hot or too cold.

With that consistently mild climate, do you even need to worry about energy efficiency?

You do if you want to lower your monthly energy costs and your impact on the environment. One way to do that is with energy efficient windows.

Multiple panes can make windows more efficient

Some of your home’s energy costs are tied to the type of window you choose. And there are many factors that affect energy efficiency. The number of panes, or layers of glass, in your window is a major one. When you start comparing the options, you’ll typically find three options:

• Single-pane — For single pane, one layer of glass separates your home from the elements. These windows are common in older homes, but less popular today due to advances in energy efficiency.
  
• Double-pane — With double-pane, or dual-pane glass, two layers of glass are held together by the frame and spacer, and within that airspace is an insulating layer of either air or gas, depending on the glass type.?
  
• Triple-pane — With triple-pane glass, three layers of glass are held together by the frame and two spacers, and within that airspace is an insulating layer of either air or gas, depending on the glass type.? That's a total of five layers of insulation, which is why triple-pane windows are the most energy-efficient.
  

With only one thin piece of glass, single-pane windows are most likely the least efficient option. An extra pane of glass — along with the insulating air or gas — helps to provide an additional layer of protection from the climate conditions of your area. So, the more panes in your window, the more energy efficient it is.

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Window labels can help tell the energy efficiency story

When you’re comparing single or multiple panes and other window features, the labels provide critical information. Every window that is certified and tested has an NFRC label that tells you its energy performance. NFRC, or National Fenestration Rating Council, is the organization that developed the energy rating program for windows. The NFRC label tells you the energy efficiency of the whole window, not just the glass.

Two very important energy performance ratings on the NFRC label are the U-Factor and the Solar Heat Gain Coefficient (SHGC). The U-Factor tells you how well the window insulates, while the SHGC rates how effective the window is at blocking the sun’s heat.

The most energy efficient windows will also have an ENERGY STAR® label. ENERGY STAR certifies a variety of products based on their ability to help save energy without sacrificing features or functionality. For windows, they divided the United States into four regions and rated products based on their energy efficiency for the region’s climate. Windows designed to keep out the cold in the northern part of the country have different requirements than those in the hot and sunny south.

SEE ALSO: Top Questions to Ask Your Window Installer

The right number of window panes for Seattle’s climate

The number of panes selected will impact the cost of the window. Generally, the fewer panes in the window, the lower the cost. However, that doesn't necessarily make a window cheaper overall.

Energy savings add up over the life of the window and can make multi-pane windows the more affordable option in the long run. Upgrading to ENERGY STAR-certified windows in the Northwest provides an average annual energy savings of $366 when you’re replacing single-pane windows. Or as much as $134 a year when you’re upgrading double-pane windows.²

In the mild Seattle climate, single-pane windows may provide all the comfort you need. Double-pane and triple-pane windows could make your home more comfortable when temperatures get out of that mild range. But you shouldn’t make your decision solely on the number of panes. Remember, it’s one of several energy efficiency factors. Different manufacturers have different energy ratings, so you’ll always want to check the U-Factor and SHGC on the window’s label.

Seattle falls into ENERGY STARs Northern region, so the ideal windows for your climate have a U-Factor less than or equal to 0.30 and an SHGC at or below 0.42. These windows let in more energy from the sun, helping to warm your home — for those 213 days of the year when it’s not raining.

¹ According to The Weather Channel
² According to information provided by Energy Star