Low-E 366 has three layers of silver. Low-E 270 has two. The extra layer blocks more summer heat and costs you only a small amount of daylight, which makes 366 the better fit for most Georgia homes. Ask which coating is standard on your quote, because every brand calls it something different.
You get three window quotes. One says Low-E 366. One says Advanced Emax. One says SunDefense. None of them explain what any of it means.
So most people skip that line and compare the frames instead. That is a mistake. The glass does most of the work in an energy-efficient window. It is also the part you cannot change later without replacing the whole unit.
The good news is that the numbers are not random. Once you know what they stand for, you can read almost any window quote and know what you are getting.
What Do the Numbers in Low-E Glass Mean?
Low-E stands for low emissivity. It is a very thin metal coating baked onto the glass. The coating reflects heat instead of letting it pass through.
The numbers tell you two things.
The first digit is how many layers of silver are in the coating. The last two digits are roughly how much visible light comes through.
So Low-E 270 has two layers of silver and passes about 70% of visible light. Low-E 366 has three layers and passes about 66%.
More silver means more heat blocked. It also means slightly less light. That is the whole trade-off.
You may also see Low-E 272 on a quote. It sits in the same two-layer family as 270. JELD-WEN lists 272 in their lineup, and Lindsay lists 270. The gap between those two is small next to the jump up to 366.
How Are Low-E 270 and Low-E 366 Actually Different?
The third silver layer is the difference, and it does real work.
JELD-WEN describes Low-E 272 as cutting window heat gain by about half compared to ordinary glass. They describe Low-E 366 as blocking up to 95% of the sun’s damaging rays.
Lindsay publishes the light numbers for the same coatings. Their LoE-270 passes 70% visible light. Their LoE-366 passes 66%.
ViWinTech puts hard numbers on it in their published performance tables. Take one of their single-hung windows with argon gas. With the two-layer coating, the U-Factor is 0.30, the Solar Heat Gain Coefficient is 0.29, and visible light is 0.54. Move to the three-layer coating on the same window, and the U-Factor stays at 0.30. The Solar Heat Gain Coefficient drops to 0.21. Visible light slips to 0.50.
Read that again, because it is the point of this whole article.
The upgrade did nothing at all for the U-Factor. It cut solar heat gain by about a quarter. And it cost four points of daylight.
Which One Is Better for Georgia Heat?
Two numbers show up on every window sticker.
U-Factor measures heat escaping your home in winter. Lower is better.
Solar Heat Gain Coefficient, or SHGC, measures how much of the sun’s heat gets in. Lower is better in a hot climate.
Here is what most people get backward. U-Factor is the number salespeople quote. SHGC is the number that matters more in Georgia.
Our summers run long, and our winters are short. Air conditioning costs more here than heat does. Blocking the sun matters more than trapping warmth.
That is the number to watch when you shop for replacement windows.
Best for most Atlanta area homes: the three-layer coating. Low-E 366, Advanced Emax, or SunDefense depending on the brand. It helps most on west-facing and south-facing glass, which takes the worst of the afternoon sun.
Best for rooms that need light: the two-layer coating. Low-E 270 or 272 makes sense on north-facing windows, in rooms shaded by mature trees, or anywhere a room already feels dark.
Plenty of homes use both. There is no rule that says every window has to match.
Why Does Every Brand Call It Something Else?
This is where people get stuck comparing quotes.
Some manufacturers use the original coating names. Some invent their own.
| Brand | Two layer coating | Three layer coating |
|---|---|---|
| JELD-WEN | Low-E 272 | Low-E 366 |
| Lindsay | LoE-270 | LoE-366 with Neat+ |
| ViWinTech | Emax | Advanced Emax |
| Pella | Advanced Low-E | SunDefense |
JELD-WEN and Lindsay name the coatings directly. ViWinTech uses their own names, but their spec sheets label Emax as the two-layer coating and Advanced Emax as the three-layer version. Pella sorts by climate instead, and lists SunDefense for very hot, sunny places.
So a quote for Advanced Emax and a quote for Low-E 366 are closer than the names suggest.
When quotes do not line up, stop comparing names. Ask each supplier for the SHGC number on that exact window. That is an independent rating, and it makes the comparison honest.
What Low-E Glass Should You Skip in Georgia?
Some coatings are built to let solar heat in on purpose. In Minnesota, that is a feature. Here it is a problem.
Pella lists their NaturalSun coating for cold climates like the far northern states and Canada. JELD-WEN offers Low-E 180, which is also a northern coating. ViWinTech marks their 180 and i89 glass packages as being for the Northern Climate Zone, and those options come back as unavailable on many of their southern configurations.
None of this is bad glass. It is just built for the bad weather.
If one of these shows up on a Georgia quote, ask why before you sign.
What Should You Ask Before You Order?
Five questions will tell you almost everything.
Which coating comes standard on this window, and which one is an upgrade?
What is the SHGC on this exact unit, in this exact size?
Which surface is the coating on? On a double-pane window, the solar coating usually sits on the second surface, counting from outside in.
Do grids change the numbers? They often do. ViWinTech’s own tables show visible light dropping when grids are added.
Can I see the NFRC label data? Those ratings are tested the same way for every brand, so they are the only fair way to compare.
Write the answers down. If two quotes still look identical after that, they probably are.
How Can Cofer Brothers Help?
We carry doors and windows from JELD-WEN, Lindsay, ViWinTech, and Pella. That means we work with all four naming systems every week, and we can tell you when two quotes are describing the same glass.
We can pull the published spec sheets for the exact window and size you are considering. Not the brochure language. The actual tested numbers.
Bring your quotes by our Tucker location, and we will read them with you. If you are working with a contractor, bring them too.
Glass options change by product line and by region, so we will confirm what is available for your specific project rather than guess.
What Should You Do Next?
Pull out the quotes you already have and find the glass line. It is usually buried near the bottom.
Look for a number. If you see 270, 272, or 366, you already know what you are looking at. If you see a brand name instead, use the chart above to place it.
Then ask for the SHGC. That one number will do more for your decision than any brochure.
If you would rather talk it through with someone, give us a call or stop by. We are happy to help you sort it out before you commit.
Related Articles
- What Is Low-E Glass and Is It Worth the Extra Cost?
- Vinyl vs Aluminum Clad Windows: What’s the Difference?
- Why Are My Windows Foggy Between the Panes?
Frequently Asked Questions
What is the difference between Low-E 270 and Low-E 366 glass?
Low-E 270 has two layers of silver and passes about 70% of visible light. Low-E 366 has three layers and passes about 66%. The third layer blocks more solar heat, so 366 keeps more summer heat out. You give up a small amount of daylight to get it.
Is Low-E 366 worth it in Georgia?
For most Atlanta area homes, yes. Georgia summers are long, and cooling costs more than heating. Low-E 366 lowers the Solar Heat Gain Coefficient, which measures how much of the sun’s heat enters your home. On one manufacturer’s spec sheet, moving from two silver layers to three dropped SHGC from 0.29 to 0.21 on the same window.
Why does every window brand use a different name for Low-E glass?
Some brands use the original coating names, and some create their own. JELD-WEN and Lindsay list Low-E 270, 272, and 366 directly. ViWinTech calls the same tiers Emax and Advanced Emax. Pella uses Advanced Low-E and SunDefense. Ask for the SHGC number instead of the brand name so you can compare quotes fairly.
Does Low-E 366 make a room noticeably darker?
The difference is small. On one ViWinTech single-hung window, visible light went from 0.54 with the two-layer coating to 0.50 with the three-layer coating. Most people do not notice it on west- and south-facing glass. In a room that already feels dark, the two-layer coating is the safer pick.
Which Low-E coatings are wrong for a Georgia home?
Coatings built to let solar heat in. Pella lists NaturalSun for cold climates like the far northern states and Canada; JELD-WEN offers Low-E 180, and ViWinTech marks its 180 and i89 packages for the Northern Climate Zone. None of it is bad glass. It is built for the wrong weather. If one shows up on a Georgia quote, ask why before you sign.
