What Is Low-E Glass and Why Does Every Colorado Home Need It?

If you have shopped for replacement windows at all, you have probably seen the term “Low-E glass” everywhere. It shows up in every brochure, every estimate, and every salesperson’s pitch. But what does it actually mean, and why does it matter so much in Colorado?

Let me explain it in plain language, the way I explain it to homeowners during consultations.

Low-E in Simple Terms

Low-E stands for “low emissivity.” Emissivity is a measure of how much heat a surface radiates. Regular glass has high emissivity, meaning it readily absorbs and re-emits heat. Low-E glass has a microscopically thin metallic coating (we are talking thinner than a human hair) that dramatically reduces how much heat the glass radiates.

Think of it like this: regular glass is like a t-shirt in winter. Heat passes right through it. Low-E glass is like a reflective emergency blanket. It lets light through but reflects heat back toward its source.

In winter, the coating reflects your home’s heat back inside instead of letting it escape through the glass. In summer, it reflects solar heat away from your home before it gets inside.

Why Low-E Is Non-Negotiable in Colorado

In many parts of the country, Low-E is a nice-to-have upgrade. In Colorado Springs, I consider it essential. Here is why.

UV Radiation at 6,300 Feet

This is the big one. At our altitude, we receive approximately 25 percent more ultraviolet radiation than homes at sea level. UV is the invisible energy that causes sunburn, and it does the same thing to your home’s interior.

Without Low-E protection, Colorado’s intense UV will:

• Fade your hardwood floors noticeably in just a few years
• Bleach your furniture fabric leaving outlines where cushions sat
• Discolor carpets especially near south and west-facing windows
• Damage artwork and photographs
• Degrade curtains and blinds making them brittle and discolored

Standard Low-E coatings block 70 to 80 percent of UV radiation. Premium coatings like Andersen’s Low-E4 block up to 95 percent. That is the difference between replacing your flooring every 10 years and having it look great for 25.

Heating Season Performance

Colorado Springs has a long heating season, roughly October through April. During those seven months, your windows are either helping you retain heat or letting it escape.

Low-E coatings reflect infrared heat (the warmth from your furnace, your body, your fireplace) back into the room instead of letting it pass through the glass to the outside. A standard double-pane window without Low-E has a U-factor around 0.47. Add Low-E coating and that drops to approximately 0.30. Add argon gas and a warm-edge spacer, and you are down around 0.25 or lower.

In practical terms, that means 40 to 50 percent less heat loss through the glass.

Cooling Season Performance

We may be a heating-dominated climate, but Colorado Springs summers are no joke either. July and August afternoon temperatures regularly hit the 90s, and south and west-facing windows can turn rooms into ovens.

Low-E coatings reduce solar heat gain by reflecting a portion of the sun’s infrared energy away before it enters your home. This means your air conditioning does not have to work as hard, your rooms stay more comfortable, and you are not fighting the sun all afternoon.

Understanding Low-E Ratings

Not all Low-E coatings are the same. Here are the two main specifications you will see:

Low-E2 (Two Layers)

This is the standard Low-E option from most manufacturers. It has two metallic coating layers applied to the glass surface. Low-E2 delivers solid performance:

• Blocks approximately 70 percent of UV
• U-factor improvement of roughly 35 percent over plain glass
• Good solar heat gain reduction
• Available on most window products at a modest upcharge

Low-E4 (Four Layers)

This is Andersen’s premium Low-E option, and it is what we install most often at Dream Windows. With four metallic coating layers, it delivers significantly better performance:

• Blocks up to 95 percent of UV
• U-factor improvement of roughly 56 percent over plain glass
• Superior solar heat gain reduction
• Keeps interior glass surface warmer in winter (better comfort, less condensation)
• Available on all Andersen product lines

The difference between Low-E2 and Low-E4 is meaningful. On a cold Colorado night, you can touch the interior glass of a Low-E4 window and it feels noticeably warmer than a Low-E2 window. Less condensation, fewer cold spots, better overall comfort.

Which Surfaces Get the Coating?

In a double-pane window, there are four glass surfaces (numbered from outside to inside):

• Surface 1: outside face of exterior pane
• Surface 2: inside face of exterior pane
• Surface 3: outside face of interior pane
• Surface 4: inside face of interior pane

For Colorado’s heating-dominated climate, Low-E coating is typically applied to Surface 3 (the inside face of the interior pane’s outer surface… I know, it gets confusing). This position maximizes heat retention during winter.

Some high-performance configurations put coatings on both Surface 2 and Surface 3 for balanced year-round performance. This is what Andersen does with their Low-E4 SmartSun glass, which is excellent for homes with significant south and west exposure.

You do not need to memorize this. Just know that when we specify windows for your home, we select the coating configuration that optimizes performance for each window’s orientation and exposure.

The ROI of Low-E Glass

Let me put some numbers to it.

The upgrade from standard glass to Low-E coating adds approximately $25 to $75 per window depending on the manufacturer and product line. For a 12-window home, that is $300 to $900 total.

The energy savings from Low-E glass in a Colorado Springs home typically run $150 to $400 per year depending on home size, window count, and current window condition.

That means the Low-E upgrade pays for itself in 1 to 3 years, and then it continues saving you money for the remaining 20 to 30 years of the window’s life. There are very few home upgrades with that kind of return.

And that calculation does not include the value of protecting your floors, furniture, and artwork from UV damage. Factor that in and the ROI is even better.

Low-E and Natural Light

One concern I hear from homeowners is: “Will Low-E make my home darker?”

No. Modern Low-E coatings are engineered to block UV and infrared while transmitting visible light almost unimpeded. A quality Low-E window transmits 70 to 76 percent of visible light, which is only slightly less than uncoated glass (about 80 to 82 percent). The difference is virtually undetectable to the human eye.

Your rooms will be just as bright and filled with natural light. The light just will not bring damaging UV and excess heat along with it.

My Recommendation

For every window we install in Colorado Springs, Manitou Springs, Woodland Park, and the surrounding areas, Low-E glass is our standard specification. We do not offer bare glass as an option because it simply does not make sense at our altitude.

For most homes, Andersen’s Low-E4 coating provides the best performance for our climate. For south and west-facing windows with heavy sun exposure, Low-E4 SmartSun adds additional solar heat rejection to keep those rooms comfortable in summer.

Want to learn more about how Low-E glass can improve your home’s comfort and efficiency? Browse our energy-efficient window upgrades and stack savings using the 2026 window replacement tax credits guide, and we will show you the difference.

See the Low-E Difference for Yourself