The Lowdown on Low-E Windows

By: Beth Krietsch Energy efficiency

Made with an extremely thin and transparent heat-reflective coating, low-emissivity (low-E) glass was developed as a way to minimize the amount of ultraviolet (UV) and infrared light that travels through a window, without compromising the amount of visible sunlight that gets in. Low-E glass windows can reduce energy costs by 12%–33%, making them one of the most energy efficient window options for homeowners.

The energy efficient glass works by reflecting the sun’s heat away from the home on warm summer days and reflecting indoor heat back into a room on cooler days, which helps maintain a consistent temperature inside the home, creating less need for the furnace or air conditioner. When a window’s emissivity is low, the home will see increased insulation from outdoor temperatures.

Because low-E windows block the sun’s UV rays, low-E windows have been found to prevent fading of furniture, carpet, and window treatments by as much as 75%. But are low-E windows right for your home? Here’s everything you’ll need to know to make an informed decision.

Types and cost of of low-E glass windows

Currently, two types of low-E glass are prominent and available at most suppliers, home improvement stores, and big-box stores. They vary in price depending on size, style, manufacturer, and type of low-E coating, but most low-E windows cost $80–$280 each.

The two most common types of low-E windows are:

  1. Passive—Very durable and commonly used in single pane windows, passive low-E windows are also referred to as hard-coat or pyrolytic due to the manufacturing process. Passive low-E windows fare best in homes in extremely cold climates as the coating allows infrared light energy through the window—which may help keep the home warm.
  2. Solar control—Never used in single pane windows, this type of low-E window is manufactured using magnetron sputtering. These soft-coat windows have lower emissivity ratings and perform better than hard-coat windows in reflecting air back into a room. Solar control low-E windows also have improved UV protection and a better U-factor rating—meaning it better insulates the room where it is installed—making this a more common choice for warmer climates. Currently, this is the most commonly used low-E glass.

How to choose low-E windows for your home

Swapping out your windows for a more energy efficient option is an excellent choice if you have the budget for the project. If you switch to low-E windows, you’ll reduce radiant heat loss and save on energy costs overall, perhaps saving enough over time to justify the up front investment.

There are many windows available. Look for the National Fenestration Rating Council (NFRC) label to determine whether a window includes a low-E coating. This label is affixed to every energy efficient window and contains key details regarding its energy rating. An ENERGY STAR label is another sign that a window is energy efficient—but may not mean that the window is necessarily a low-E window. Of course, according to ENERGY STAR, low-emissivity glass is a common feature of an energy-efficient, high-performing window.

To determine whether it makes sense to install new windows, consider the total cost of the project, including purchasing the windows, any labor costs associated with installation, and any warranty costs. Calculate your estimated energy savings. Using this information to assist in making a decision ensures that you’ll know whether installing low-E windows is your next home improvement project.  

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