Low-E glass windows are one of the most important energy-saving technologies available to Minnesota homeowners today, and understanding how they work will help you make smarter decisions during your next window replacement project. Low-E, which stands for low emissivity, refers to a microscopically thin metallic coating applied to window glass that dramatically reduces heat transfer while still allowing visible light to pass through. At Weatherguard Construction, we have been installing high-performance low-E glass windows in homes across Stillwater, Woodbury, Minneapolis, and throughout the Twin Cities metro for over 25 years.

What Is Low-E Glass?

Low-E glass features an ultra-thin coating of metallic oxide, typically silver or tin oxide, applied to one or more surfaces of the glass. This coating is nearly invisible to the naked eye but has a profound effect on how the window manages heat energy. The coating works by reflecting infrared heat radiation while allowing visible light to pass through, essentially acting as a selective filter for different wavelengths of energy.

There are two types of low-E coatings:

Passive low-E (hard coat): Applied during the glass manufacturing process by depositing the coating on molten glass. Hard-coat low-E is durable and scratch-resistant but slightly less effective at heat reflection. It is best suited for cold climates where maximizing solar heat gain in winter is desirable.

Solar control low-E (soft coat): Applied after manufacturing in a vacuum chamber using a process called sputtering. Soft-coat low-E offers superior performance with multiple layers of silver that provide excellent heat reflection. It must be sealed within an insulated glass unit to protect the delicate coating. This is the most common type used in modern high-performance windows.

How Low-E Glass Saves Energy in Minnesota

Winter Heat Retention

During Minnesota's long, cold winters, low-E glass reflects radiant heat from your furnace and interior surfaces back into your home rather than allowing it to escape through the window. Without low-E coating, a significant percentage of your heating energy radiates directly through the glass and is lost to the outdoors. With low-E glass, that radiant energy is reflected inward, keeping your home warmer and reducing the load on your heating system.

In practical terms, a window with low-E glass can reduce heat loss through the glass by 30 to 50 percent compared to uncoated glass. For Minnesota homeowners who rely on forced-air furnaces or boilers for six or more months per year, this translates into measurable energy savings and improved comfort.

Summer Heat Rejection

Low-E glass also works in reverse during summer. The coating reflects a significant portion of the sun's infrared radiation away from your home, reducing solar heat gain that would otherwise force your air conditioning to work harder. This is particularly valuable on south-facing and west-facing windows that receive intense afternoon sun during Minnesota's warm months.

UV Protection

Low-E coatings block up to 95 percent of ultraviolet radiation from entering your home. UV rays are the primary cause of fading in furniture, carpeting, hardwood floors, and artwork. By filtering UV radiation, low-E glass protects your interior furnishings and finishes, preserving their appearance and extending their lifespan.

Understanding Low-E Glass Performance Ratings

When shopping for energy-efficient windows, several key ratings help you compare low-E glass performance:

U-Factor: Measures how well a window prevents heat from escaping. Lower numbers indicate better insulation. Minnesota Energy Code requires a U-factor of 0.30 or less. Premium windows from Pella, Marvin, Kolbe, and Andersen with advanced low-E glass can achieve U-factors as low as 0.15 to 0.20.

Solar Heat Gain Coefficient (SHGC): Measures how much solar radiation passes through the window. In Minnesota, a moderate SHGC of 0.25 to 0.40 is typically recommended to balance winter solar heat gain with summer heat rejection.

Visible Transmittance (VT): Measures how much visible light passes through the glass. Higher VT values mean more natural light. Modern low-E coatings achieve excellent heat management while maintaining VT values of 0.40 to 0.55, providing abundant natural daylight.

Low-E Glass Options by Number of Panes

Double-Pane with Low-E

Double-pane windows with low-E coating on one surface and argon gas fill between the panes represent the standard for energy-efficient windows today. This configuration delivers a significant improvement over older single-pane or non-coated double-pane windows and meets Minnesota Energy Code requirements.

Triple-Pane with Low-E

Triple-pane windows with low-E coatings on two or more surfaces and argon or krypton gas fills between all three panes deliver the highest level of thermal performance available. This configuration can achieve U-factors below 0.20, providing exceptional insulation for the coldest Minnesota winters. Weatherguard Construction recommends triple-pane low-E glass for homeowners who prioritize maximum energy efficiency and comfort.

Which Low-E Glass Is Right for Your Minnesota Home?

The optimal low-E glass package depends on your specific situation:

  • North-facing windows: Choose low-E glass with a lower U-factor for maximum insulation, since these windows receive minimal direct sunlight
  • South-facing windows: A slightly higher SHGC allows beneficial passive solar heating during winter while low-E coating still provides summer heat rejection
  • West-facing windows: Prioritize solar control low-E with lower SHGC to manage intense afternoon heat in summer

All four premium brands that Weatherguard Construction installs, Pella, Marvin, Kolbe, and Andersen, offer multiple low-E glass packages optimized for cold-climate performance. Our team will help you select the right glass configuration for each window in your home.

The Full Frame Difference

Low-E glass delivers maximum benefit when installed as part of a full frame window replacement. Unlike insert replacements that leave the old frame in place, full frame replacement allows Weatherguard Construction to properly insulate the rough opening, install flashing, and ensure an airtight seal around the entire window unit. This prevents air leakage that would undermine the energy savings provided by your low-E glass.

Contact Weatherguard Construction at (651) 439-4320 or book a free consultation to learn which low-E glass options are best for your home. We serve Minnesota from our Stillwater headquarters, plus Schaumburg, IL and Centennial, CO.

Frequently Asked Questions

Can you see low-E coating on windows?

Low-E coating is nearly invisible. You may notice a very slight tint or color shift when viewing the glass at an angle, but in everyday use, low-E windows appear clear and provide excellent natural light. The coating does not significantly darken or distort your view.

Does low-E glass cost more than regular glass?

Yes, low-E glass adds approximately $25 to $75 per window compared to uncoated glass. However, the energy savings typically recoup this cost within two to four years, making low-E glass one of the best investments you can make in your windows.

How long does low-E coating last?

Low-E coating is sealed within the insulated glass unit and is designed to last the lifetime of the window, typically 25 to 40 years or more. The coating does not wear off, peel, or degrade under normal conditions because it is protected between the panes of glass.

Is low-E glass required by code in Minnesota?

While low-E glass itself is not specifically required, the U-factor and SHGC performance standards in Minnesota Energy Code effectively require low-E glass to meet compliance. Virtually all new and replacement windows installed in Minnesota today include low-E glass as standard.