How to pick out energy-efficient windows

Energy-efficient windows provide many benefits. By helping to keep heated and air conditioned air inside your home (and outside air outside) they can make your home’s temperature more comfortable, especially when they’re incorporated into a home whose overall design is efficient.

Energy-efficient windows can also help reduce utility bills and increase your property’s value, helping you saving money over time. So, what is an energy-efficient window? The short answer is a well-designed window that’s thermally broken (designed to block energy transfer between inside and outside) and features glass that is energy efficient. Glass is a vital part of the equation because it’s what most of a window surface area consists of. There are multiple ways to improve glass efficiency, which we’ll get into below. 

When it comes to energy efficiency, there are multiple factors that affect window performance, including: the type of window, window glass, and accessory selections, like grilles. We’ll explain what to focus on in order to pick out the most energy-efficient windows for your home, including climate-specific selections.  

Glass is a key element of energy efficiency. The panes (sheets of glass) in a window and the air space in between together make up an insulated glass unit (IGU). Here’s what you need to know about the IGUs we offer: 

	Dual-pane	Triple-pane
What is it?	A dual-pane, or double-pane, IGU is made of two panes of glass with an air space in between. The air space in our windows is usually filled with an argon-gas blend that provides extra insulation because it’s denser than air. It comes standard with Low-E/Low-E4® glass to further boost efficiency. Other climate-specific Low-E glass is also available.	A triple-pane IGU has three panes of glass and two air spaces in between. The air spaces are usually filled with an argon-gas blend. Triple-pane comes standard with Low-E/Low-E4 glass. If additional thermal performance or climate-specific performance is required or desired, there are multiple Low-E glass options that can be selected.
Cost	A dual-pane IGU is the most cost-effective choice and is a good option if you live in a warmer climate.	A triple-pane IGU is more expensive than a dual-pane IGU because it uses more materials.
Energy efficiency	While a dual-pane IGU is less energy efficient than a triple-pane IGU, it can offer the performance needed in warmer climates where you need less insulation.	A triple-pane IGU is the most energy efficient due to the additional air space and opportunity to add more Low-E coating combinations. It’s most impactful in northern climates.
Soundproofing	A dual-pane IGU won’t reduce sound transmission as much as triple-pane.	A triple-pane IGU adds thickness that helps muffle sound.
Install Considerations	Dual-pane is standard across the window and door industry, so installing a window with this type of IGU won’t add complication.	A triple-pane IGU is 1.5 times heavier than a dual-pane IGU. The heavier weight could increase install costs due to the need for additional labor or equipment.
Products	Dual-pane comes standard with all our windows and doors.	You can find triple-pane glass IGUs available with our E-Series Series, A-Series, and 400 Series windows and doors. Triple-pane is also available with select 100 Series windows and 200 Series doors.

Simply put, this is how well your window keeps heat (or energy) inside the home. If you want to understand this further, a U-Factor value is the measure used to determine how well a window or door prevents heat from escaping. The lower the number, the less heat is being lost. Understanding U-Factor values is helpful if you want to comparison shop between window brands. 

For the most accurate measurement of performance, it’s very important to look at the U-Factor value for the whole window (called “whole unit performance”), not just the center of glass, which is a measurement you might come across. When comparing performance across manufacturers, make sure you have whole unit performance for all products you’re evaluating. 

One of the ways windows can be optimized for a specific climate zone is with glass coatings. Low-E/Low-E4 glass coatings come standard with our windows. They are ultra thin, generally transparent, and improve window efficiency. These coatings work by reflecting or absorbing heat. They can also be combined so different coatings are used on different panes of glass in order to help create optimal performance. 

One of the reasons triple-pane windows offer such superior performance is because the third pane offers an additional opportunity to include Low-E coatings. Here is what you need to know:

Low-E coatings for cold climates 

Depending on the conditions, it might make sense to consider a coating that will help heat up the home in the winter, or one that will help protect the home further from the sun’s intensity. Consider the following: 

The combination of PassiveSun glass with HeatLock technology can be a good one in a Northern climate, because it can help insulate the home while also heating it with the power of the sun. This combination might be useful in a home that’s been designed according to passive house principles.

Low-E coatings for mild to hot climates

There are specific glass coatings that can help keep the sun from heating your home too much and even help reduce harmful UV rays from coming into your home, including: 

As you’ve no doubt gathered, windows can be customized for energy-efficient performance in many different ways. Two additional selections that can have a big impact are grilles and breather tubes. You can forego grilles or select a more energy-efficient option, see below, but breather tubes are typically required at high altitudes. However, if you’re aware of the effect these features have, you can make other selections to counter their impact on performance.

Grilles: When they touch both panes of glass, these ornamental bars decrease efficiency by conducting energy and decreasing the insulating power of the air space. This is why the energy spacer bars available with A-Series windows and doors were designed in a way that avoids touching the glass. They’re a great option if you want the authentic look of full divided light grilles. But the most efficient choice of all is to skip grilles altogether.

Breather tubes: At elevations above 4,00 feet, these tubes prevent windows from becoming pressurized by allowing air to escape from the space in between window panes. Windows created for these elevations don’t include the argon-gas blend typically added to the air space in our windows, so they are less efficient overall. But don’t worry if you live at high altitude, you can lean into the selections highlighted above to help improve energy efficiency when breather tubes are required.