Identifying Low-E on Installed Windows

Why This Matters More Than You Think

Here is the uncomfortable reality for a lot of Toronto homeowners: you have no idea what glass is in your windows.

Maybe you bought the house in 2014 and the listing said "upgraded windows." Maybe a contractor replaced them in 2019 and said "energy efficient." Maybe you inherited the place from your aunt and the windows have been there since Chrétien was Prime Minister.

None of that tells you whether your glass has a Low-E coating. And without Low-E, your windows are letting roughly 40-50% more heat escape than they should be. In a Toronto winter where your furnace is running from November to April, that is real money leaving through the glass.

The good news: you can detect Low-E glass in about 30 seconds with a Bic lighter. No tools. No expertise. No calling anyone.

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The Lighter Test: Step by Step

What You Need

• A lighter or match (a candle works too, but the small flame is easier to read)
• Darkness or low light (do this at night or in a dark room)
• A double-pane window (which is virtually every residential window installed in Ontario since the mid-1990s)

What You Do

1. Hold the lighter about 2-3 inches from the glass. Do not touch the glass with the flame. Just get it close.
2. Look at the reflections. You will see four small images of the flame. Two are reflected off the outer pane (Surfaces 1 and 2), and two off the inner pane (Surfaces 3 and 4).
3. Compare the colours. If all four reflections are the same orange-yellow colour, the glass has no Low-E coating. If one reflection is a noticeably different colour—typically a muted purple, blue-green, or pinkish hue—that surface has a Low-E coating.
4. Note which reflection is different. Count from the outside in. If it is the second or third reflection, that tells you which surface the coating sits on.

That is the whole test.

Why Does One Reflection Look Different?

Low-E stands for "low emissivity." The coating is an ultra-thin layer of metallic oxide—usually silver—that is essentially invisible to the naked eye. But it interacts with light differently than bare glass.

Regular glass has an emissivity of about 0.84. That means it absorbs and re-radiates 84% of the infrared (heat) energy that hits it. A Low-E coating drops that emissivity to roughly 0.02 to 0.04. Instead of absorbing heat, it bounces it back like a mirror.

When your lighter flame hits a Low-E coated surface, the metallic layer reflects certain wavelengths differently than the bare glass surfaces. The result: one reflection looks like it is wearing slightly tinted sunglasses while the other three are naked.

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Understanding the Four Surfaces

Every double-pane insulated glass unit (IGU) has four glass surfaces. This trips people up, so let me be specific.

Surface Numbering (Outside to Inside)

Surface	Location	Description
Surface 1	Exterior face of the outer pane	Faces the weather
Surface 2	Interior face of the outer pane	Faces the air gap
Surface 3	Exterior face of the inner pane	Faces the air gap
Surface 4	Interior face of the inner pane	Faces your living room

The Low-E coating almost always goes on Surface 2 or Surface 3. Never Surface 1 (too exposed to weather) and rarely Surface 4 (would interfere with interior cleaning and add no meaningful benefit).

Which Surface for Toronto?

This is where climate matters.

Surface 3 (heating-dominated climates like Toronto): The coating sits on the inner pane's gap-facing side. It reflects your furnace heat back into the house while allowing solar heat gain through the outer pane. This is what you want when January hits -22°C and your heating bill looks like a car payment.

Surface 2 (cooling-dominated climates like Phoenix): The coating sits on the outer pane's gap-facing side. It blocks solar heat from entering. Useful if your priority is keeping heat out.

Most windows installed in the GTA over the last 15 years have Low-E on Surface 3. If your lighter test reveals that the third reflection (counting from outside) is the different one, your windows are configured correctly for our climate.

Quotable: A Low-E coating on the wrong surface is like wearing your winter jacket inside out. It still looks like a jacket. It just does not keep you warm.

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Hard Coat vs. Soft Coat: The Two Types of Low-E

Not all Low-E coatings are manufactured the same way. There are two distinct technologies, and they perform differently.

Hard Coat (Pyrolytic) Low-E

The coating is applied during glass manufacturing while the glass is still molten on the float line. A chemical vapour bonds directly to the glass surface, becoming part of the glass itself.

Characteristics:

• Extremely durable. You can handle it, touch it, even clean it without damage.
• Can be used in single-pane applications (no IGU required).
• Higher emissivity than soft coat (typically 0.15-0.20 vs. 0.02-0.04).
• Allows more solar heat gain—good for passive solar in cold climates.
• Cardinal's LoE-180 is the most common hard-coat product in Canadian residential windows.

Soft Coat (Sputtered) Low-E

The coating is applied after manufacturing in a vacuum chamber using a process called magnetron sputtering. Atoms of silver are literally blasted onto the glass surface in ultra-thin layers.

Characteristics:

• Much lower emissivity (0.02-0.04). Better thermal performance.
• Fragile. Must be sealed inside an IGU—you cannot touch it.
• Multiple silver layers possible (double-silver, triple-silver coatings).
• Cardinal's LoE-366 uses three layers of silver for year-round performance.
• Slightly better UV blocking (up to 95%).

Which One Is in Your Windows?

If your windows were installed by a reputable manufacturer in the GTA after 2010, they almost certainly have soft-coat Low-E. Hard coat is still used, but it is becoming the exception rather than the rule for residential work.

The lighter test cannot tell you which type you have. It only tells you the coating exists. To know the exact product, you would need the manufacturer's sticker (usually on the spacer bar between the panes) or the original purchase documentation.

Quotable: Hard-coat Low-E is the cast-iron pan of the glass world—tough, reliable, a bit old-school. Soft-coat is the non-stick ceramic—better performance, but you need to treat it right.

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Cardinal LoE-180 vs. LoE-366: What Toronto Contractors Spec

Cardinal Glass Industries manufactures the Low-E coatings used in the majority of Canadian residential windows. Two products dominate the Toronto market.

LoE-180 (The Cold Climate Specialist)

• U-Factor: 0.26 (excellent insulation)
• SHGC (Solar Heat Gain Coefficient): 0.69 (lets lots of solar heat in)
• Best for: North-facing rooms, passive solar designs, homes that want free winter heat from the sun
• Trade-off: Lets more summer heat in too

LoE-180 uses a single layer of silver. It is designed specifically for heating climates. The high SHGC means your south-facing windows are essentially free solar panels in January. The catch? Those same windows will heat your living room like a greenhouse in July if you do not have overhangs or blinds.

LoE-366 (The All-Climate Performer)

• U-Factor: Comparable to LoE-180 when paired with argon
• SHGC: 0.27 (blocks most solar heat)
• UV Blocking: 95%
• Best for: Year-round comfort, furniture protection, homes with large west-facing windows

LoE-366 uses three layers of silver (that is what the "3" in the name refers to). It blocks infrared heat from both directions—keeping furnace heat in during winter and solar heat out during summer. It also blocks 95% of UV rays, which is why your hardwood floors and leather couch will not fade as fast.

So Which Should Toronto Homeowners Choose?

For most GTA homes, LoE-366 is the better all-around choice in 2026. Toronto is not Sudbury. We get legitimate summer heat, and with climate trends pushing our cooling season longer every year, the balanced performance of LoE-366 outperforms LoE-180 for whole-year energy savings.

The exception: if you are building a passive solar home or have large south-facing windows with proper overhangs, LoE-180 can be a strategic choice for those specific openings.

If you want to understand how the argon gas fill between the panes works alongside these coatings, we broke down the physics of argon and Low-E in detail here.

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What If Your Windows Fail the Lighter Test?

You did the test. All four reflections are the same colour. No Low-E.

Here is what that means in practical terms.

The Energy Penalty

A standard double-pane window without Low-E and argon typically has a U-factor around 0.47-0.50. A modern Low-E and argon unit hits 0.25-0.30. You are losing roughly 40% more heat through every window opening compared to current standards.

For a typical 2,000 sq ft Toronto home with 15-20 windows, that translates to an estimated $400-700 per year in wasted heating and cooling energy. Over 10 years, that is $4,000-7,000. At some point, the windows pay for themselves.

The Comfort Penalty

Beyond dollars, non-Low-E windows create cold spots. Stand next to a large window on a -15°C night and you can feel the chill radiating off the glass. That radiant cold makes the room feel 3-5 degrees cooler than the thermostat says, so you crank the heat higher, burning even more gas.

Low-E eliminates that cold radiation effect. The inner surface of a Low-E window stays significantly warmer, which is why rooms with upgraded glass feel more comfortable even at the same thermostat setting.

Your Options

1. Full window replacement. New frames, new glass, new everything. This makes sense if your frames are also deteriorating—rotting wood, cracked vinyl, failed seals with visible fogging.
2. Glass-only replacement. If your frames are still solid, we can replace just the sealed glass unit with a new Low-E and argon IGU. Faster, less expensive, less disruption.
3. Do nothing (for now). If you are planning to sell in the next 2-3 years, it may not pencil out. But know what you have.

Quotable: Windows without Low-E in 2026 are like running a furnace with the damper half-open. The system works. It just wastes a third of the energy.

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The ENERGY STAR Connection

ENERGY STAR Canada simplified its window requirements in 2020 by eliminating regional climate zones. Now there is one national standard.

To earn the ENERGY STAR label in Canada, a window must hit a U-factor of 1.22 W/m²K or lower (that is 0.21 in imperial). For the "Most Efficient" designation, it is 1.05 W/m²K or lower.

You simply cannot hit these numbers without Low-E glass. It is not technically mandated by name, but it is mandated by physics. No manufacturer is meeting those U-factor targets with clear glass and air fill.

Ontario's SB-12 supplementary standard takes things further for new construction. Every window going into a new build or major renovation in the GTA needs to meet or exceed ENERGY STAR requirements. Low-E is not optional—it has not been optional for over a decade.

If you want to understand what all those numbers on the ENERGY STAR sticker mean, we have a plain-English breakdown of window energy ratings.

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Triple Pane: Six Reflections, Two Coatings

If you have triple-pane windows (increasingly common in new GTA construction), the lighter test still works—but you will see six reflections instead of four. Triple-pane IGUs have six glass surfaces, and typically two of them have Low-E coatings (usually Surfaces 2 and 5).

With triple pane, you should see two reflections that are a different colour. If you only see one, or none, something is off. Either the glass was not specced correctly, or you might actually have a double-pane unit despite what the builder told you. It happens more often than you would think.

Quotable: Six reflections, two odd colours—that is how you confirm triple pane without pulling out a tape measure.

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Common Mistakes When Doing the Test

Testing in bright daylight. The colour difference is subtle. Ambient light washes it out. Do this at night.

Using an LED flashlight. LEDs produce a narrow spectrum. A flame produces a broad spectrum that makes the colour shift more visible. A white LED held very close will work in a pinch, but it is harder to read.

Expecting a dramatic colour change. We are not talking neon green vs. orange. The difference is subtle—a slight shift in hue. Once you see it on one window, you will recognize it everywhere.

Only testing one window. Not all windows in your home may have the same glass. Previous owners may have replaced some windows and not others. The kitchen might have Low-E while the basement still has the original 1995 clear glass. Test every window.

Confusing tinted glass with Low-E. Some windows have grey or bronze tinted glass for privacy or glare reduction. Tinted glass is not Low-E. Tinting is in the glass itself and affects visible light. Low-E is a surface coating that primarily affects infrared. You can have tinted glass without Low-E, Low-E without tinting, or both.

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When to Call a Professional

The lighter test tells you whether Low-E is present. It does not tell you:

• The specific product (LoE-180, LoE-366, AGC Comfort, PPG Solarban, etc.)
• Whether the argon gas fill is still intact
• The actual U-factor of the installed unit
• Whether the seal has failed (early-stage seal failure can be invisible)

If you are making decisions about replacement, renovation, or an insurance claim, you need more than a lighter test. A window professional can read the spacer bar markings, check for gas fill with specialized equipment, and give you actual performance numbers.

We do free glass assessments across the GTA. If your lighter test comes back with four matching reflections—or you just want to know exactly what you have—get in touch for a consultation. No pressure, no sales pitch on the first visit. Just information.

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FAQ

Can I detect Low-E glass without a lighter? Yes, but it is harder. You can hold a white piece of paper against the glass and look for a faint colour shift in the reflection compared to the opposite pane. A lighter or match is more reliable because the flame's colour contrast is sharper.

Does Low-E glass look different from regular glass? Barely. Modern soft-coat Low-E has a very slight greenish or bluish tint, but most people cannot tell it apart from clear glass by eye alone. The lighter test is the only reliable DIY method.

Which surface should the Low-E coating be on for Toronto windows? For heating-dominated climates like Toronto, the coating typically goes on Surface 3—the inner face of the interior pane. This reflects your furnace heat back inside while still letting beneficial solar heat in through the outer pane.

Can Low-E coating wear off over time? Soft-coat Low-E is sealed inside the insulated glass unit, so it cannot be touched, scratched, or degraded by weather. Hard-coat (pyrolytic) Low-E is baked into the glass itself. Neither wears off. If your seal fails and the unit fogs up, the coating is still there—your problem is moisture, not coating loss.

Is Low-E glass required by Ontario building code? Ontario's SB-12 energy code effectively requires Low-E glass because you cannot hit the mandated U-factor targets without it. No builder in the GTA has installed non-Low-E residential windows in over a decade.

Will Low-E glass interfere with my phone signal or Wi-Fi? Low-E coatings contain metallic layers (usually silver) that can attenuate some radio frequencies. In practice, the effect on Wi-Fi and cell signal is minor for most homes. If you have spotty reception already, it is worth considering—but it is rarely a dealbreaker.