What is Low-E glass and how does it work? Energy savings explanation for Chicagoland homeowners considering window replacement.
You've seen "Low-E glass" mentioned in every window brochure, but what does it actually do and why does it matter in Illinois? Here's the clear explanation.
What Low-E Means
Low-E stands for "low emissivity." It refers to a microscopically thin metallic coating applied to the glass surface that reflects certain wavelengths of energy. The coating is invisible to the naked eye — you can't see it or feel it on the glass.
How It Works in Winter
In winter, Low-E coating reflects heat (infrared radiation) from your heating system back INTO your home instead of letting it escape through the glass. Your furnace heats the room, that heat hits the window glass, and instead of passing through to the cold outside, the Low-E coating bounces it back inside. Result: your home stays warmer with less heating energy.
How It Works in Summer
In summer, the same coating reflects the sun's heat (solar radiation) AWAY from your home before it enters through the glass. The sun beats down on your windows, and instead of turning your rooms into a greenhouse, the Low-E coating blocks a significant percentage of solar heat gain. Result: your AC works less hard and your rooms stay cooler.
Low-E + Argon Gas + Triple-Pane
The combination of Low-E coating, argon gas fill between panes, and triple-pane construction creates the highest-performing glass package available. Each technology addresses a different type of energy transfer: Low-E handles radiation, argon gas reduces convection, and the triple-pane configuration reduces conduction. Together, they cut energy loss through windows by 25-40%. Are triple-pane windows worth it? →
All of the Andersen windows we install include Low-E glass as standard. Learn about our window installation →
Reading the label
Every new window carries an NFRC label with two numbers that matter here. U-factor measures how easily heat passes through: lower is better, and it is the key number for our winters. Solar heat gain coefficient (SHGC) measures how much of the sun's heat gets in: lower keeps rooms cooler in summer, slightly higher can help on a sunny winter day. Comparing those two numbers lets you judge windows across brands on equal terms.
Where the savings really come from
Glass is only part of it. A window that is not air sealed and insulated around the frame leaks no matter how good the glass is, which is why installation matters so much. The biggest gains come from replacing single-pane or failed double-pane units. Going from a good double-pane Low-E window to triple-pane is a smaller step that pays back mostly in comfort and noise reduction.
Where exterior money goes furthest
For how a house looks from the street, the front door, garage door and siding color do the most. For comfort, windows and air sealing. For protecting the building, roof, gutters and flashing. For resale, national cost-versus-value surveys consistently put entry doors, siding and windows near the top for the share of cost recovered. A good plan fixes anything leaking first, then spends on what you will see and feel every day.
Plan the whole house, then phase it
Even if you will do one project a year, decide the end result first: roof color, siding color, trim and window finish. Then each phase fits the next and nothing has to be redone. Tell your contractor the full plan. We keep measurements, product lines and colors on file so that the windows installed next year match the ones installed this year.
Common questions
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