For a Minnesota house, put a high-solar-gain Low-E (Cardinal LoE-180, Andersen PassiveSun, Pella NaturalSun, Marvin Low E1) on south-facing glass that sees winter sun, a moderate or low-solar-gain coating (LoE-272 or 366, Andersen Low-E4 or SmartSun, Pella Advanced Low-E, Marvin Low E2 or E3) on west glass and rooms that overheat, and on north glass chase the lowest U-factor, since there is no sun to harvest.
A room-side surface-4 coating lowers the U-factor further wherever heat loss matters more than sun. This assumes you already know what a Low-E coating is and what SHGC means. If not, start with jmbbuildersmn.com/blog/low-e-glass-argon-windows-explained and jmbbuildersmn.com/blog/window-energy-ratings-explained. This post is about the choice most window quotes skip: which coating, on which surface, on which side of the house.
What does a Low-E coating do, and what is surface 2 vs. 3 vs. 4?
A Low-E coating is a microscopically thin stack of metal and metal-oxide layers, usually built around silver, that lets visible light through while reflecting long-wave heat. In winter it reflects room heat back into the room. In summer it reflects the sun's heat back outside. How much of the sun's heat it lets in is the SHGC; how well it slows heat loss is the U-factor.
Where the coating sits changes what it does. Surfaces are numbered from the outside: surface 1 is the outdoor face of the outer pane, surface 2 is its inner face (looking into the gap), surface 3 is the gap side of the inner pane, and surface 4 is the face you touch from the room. Soft-coat Low-E is delicate and lives inside the sealed unit, on surface 2 or 3. A coating on surface 2 intercepts the sun before it enters the gap, so it gives a lower SHGC. The same coating on surface 3 lets the sun warm the gap first and gives a higher SHGC. Cardinal's own data shows the higher solar gain when its coatings are on surface 3 rather than 2.
Surface 4 is different. It is exposed to the room, so it takes a hard, durable coating like Cardinal's LoE-i89. A surface-4 coating reflects room heat back inside and lowers the U-factor without changing the solar gain much. Andersen sells it as HeatLock and Marvin as ERS. It comes with one caveat: the room-side glass runs a little colder because less heat reaches it, which raises the chance of surface condensation in a humid house. Manufacturers say so themselves and suggest pairing it with an air exchanger or dehumidifier.
High-solar-gain vs. low-solar-gain: what is the real difference?
Both types insulate about the same. The difference is how much sun they let through, and the numbers make it concrete. Cardinal publishes center-of-glass figures for a double-pane argon unit with each coating on surface 2:
| Coating | Type | SHGC | U-factor | Where it fits in Minnesota |
|---|---|---|---|---|
| LoE-180 | High solar gain | About 0.69 | About 0.26 | South glass with winter sun; passive solar; rooms that run cold |
| LoE-272 | Moderate solar gain | About 0.40 | Similar to 180 | East, and general-purpose glass where you want some sun but not overheating |
| LoE-366 | Low solar gain | About 0.27 | About 0.24 | West glass, large exposures, rooms that overheat, fading concerns |
| LoE-366 plus i89 on surface 4 | Low gain, lowest U | About 0.25 | About 0.20 | North glass and anywhere the U-factor matters more than the sun |
Which Low-E coating for north-facing windows?
North glass in Minnesota gets diffuse daylight and almost no direct sun in any season. There is nothing to harvest, so SHGC is nearly irrelevant and heat loss is everything. Pick the coating and package with the lowest U-factor the frame can carry: a low-gain coating on surface 2 with a surface-4 coating, or triple-pane, or both. The north side is also where a warm-edge spacer earns its keep, because the glass edge is coldest there and condensation shows first.
There is one argument against a surface-4 coating on the north: it lowers the room-side glass temperature slightly and north glass is already the coldest in the house. In a tight house with high winter humidity, that can mean more condensation at the bottom of the pane. Triple-pane avoids that trade-off, since the inner pane sits behind two gas spaces and runs warmer. If you are choosing between them for a north bedroom, triple-pane is the more comfortable answer.
Which Low-E coating for south-facing windows?
South glass is where Minnesota gets something back. The winter sun is low and hits south windows nearly square on for hours, and a high-solar-gain coating like LoE-180, PassiveSun, NaturalSun or Marvin Low E1 lets most of that heat in. On a clear January afternoon a south room with high-gain glass can hold temperature with the heat off. This is also why ENERGY STAR Version 7.0 added a minimum SHGC for the Northern zone; the program wants that sun used.
The trade-off is summer. The sun is high in June, so overhangs, roof eaves and even a modest porch roof shade south glass for much of the day. If the south wall has deep eaves, high-gain glass is an easy call. If it is a two-story wall with no overhang and a big picture window, moderate-gain glass like LoE-272 is a safer middle. Fading of floors and fabrics is the other consideration: high-gain coatings block less UV than low-gain ones, so a south room with hardwood and a favorite couch may want the moderate option.
What about east- and west-facing windows?
West is the problem side. The afternoon sun is low, hot and comes in nearly horizontally through a west window in July and August, when the house is already warm. A low-solar-gain coating like LoE-366, SmartSun, SunDefense or Marvin Low E3 keeps a west living room usable without running the air conditioner from three o'clock on. In winter the west sun is weak and brief, so you give up little by blocking it.
East is gentler. Morning sun is cooler and the house has cooled overnight, so most people like it. A moderate coating like LoE-272 or Marvin Low E2 lets a kitchen or breakfast area warm up in the morning without the west-side overheating. If the east side has large glass and no shade, treat it like the west.
The practical result for a whole-house order is usually two or three coatings: high or moderate gain on the south, low gain on the west, and the lowest U-factor package on the north, with east matching either the south or the west depending on shade. Every major manufacturer will build this; you just have to ask for it per opening.
What do the manufacturer coating names mean?
Cardinal Glass makes the coatings used by many window brands, and each brand puts its own name on the package. The table maps the common names to what they are for. Exact SHGC and U-factor depend on the pane count, gap, spacer and frame, so confirm the NFRC numbers for your series.
| Manufacturer | High solar gain | Moderate / all-purpose | Low solar gain | Room-side (surface 4) |
|---|---|---|---|---|
| Cardinal (glass maker) | LoE-180 | LoE-272 | LoE-366 | LoE-i89 |
| Andersen | PassiveSun | Low-E4 (standard on 400 Series) | SmartSun (blocks about 95% of UV) | HeatLock (Cardinal i89 on surface 4) |
| Pella | NaturalSun (blocks about 69% of UV; has a room-side layer) | Advanced Low-E; AdvancedComfort Low-E (recommended for northern climates) | SunDefense (blocks about 94% of UV) | Included in some packages; ask for the surface layout |
| Marvin | Low E1 (for colder climates) | Low E2 (standard, with argon) | Low E3 (warm, intense sun) | ERS, offered with Low E2 or Low E3 |
Why do most quotes put one coating on the whole house?
Because it is easier to order, easier to price and nobody asked. A single low-gain coating everywhere is the safe default for a salesperson: no overheating complaints, no fading complaints, a good U-factor on every label. In a heating climate it leaves some free winter heat on the south side unused, and it may make the north side no better than it needs to be.
Mixing by elevation costs nothing extra on most order forms; the coatings are line-item options per window. What it takes is a plan. Walk the outside of the house with the quote and mark each opening with its compass direction and its shade. Then assign a coating per elevation and have the quote list it per window. If you are buying the windows yourself for a labor-only install, this is the step to do before you place the order, because glass cannot be changed after the unit is built.
Two cautions. First, keep the same coating within a single view, since high- and low-gain glass have a slightly different tint. Second, a coating change can change the ENERGY STAR status of an individual window; the label follows the glass package, so check that every unit on the order still meets the Northern criteria if the label matters to you or to a rebate.
What JMB Builders does
JMB Builders is a licensed Minnesota residential building contractor (BC809005) based in Zimmerman, working across the Twin Cities metro. We install every brand and are a dealer for none, so we will help you mark coatings by elevation on your own order. One crew measures, installs and trims. Paid by check or direct deposit. Call 763-204-2099 or send photos through the site.
- Labor-only installation of windows you bought at a store or online — jmbbuildersmn.com/services/labor-only
- Which windows to buy for a labor-only install, including glass options by brand — jmbbuildersmn.com/services/labor-only/which-window-brand-to-buy-for-labor-only-install
- Insert and full-frame replacement windows and doors, measured and ordered by us — jmbbuildersmn.com/services/full-service
- Pella 250 Series installation, labor only — jmbbuildersmn.com/services/labor-only/pella-250-window-install-labor-only
- Send three photos, written quote within one business day.
Frequently asked questions
What is the best Low-E coating for a cold climate like Minnesota?
There is not one. South glass that gets winter sun does best with a high-solar-gain coating such as Cardinal LoE-180, Andersen PassiveSun, Pella NaturalSun or Marvin Low E1. West glass and rooms that overheat want a low-gain coating such as LoE-366, SmartSun, SunDefense or Marvin Low E3. North glass wants the lowest U-factor available, often a surface-4 coating or triple-pane, since there is no sun to harvest.
What is the difference between Cardinal LoE-180, 272 and 366?
They are the same family of soft-coat Low-E with increasing solar control. Cardinal's center-of-glass data for a double-pane argon unit puts LoE-180 at an SHGC around 0.69, LoE-272 around 0.40 and LoE-366 around 0.27. U-factors are similar, roughly 0.24 to 0.26. The choice is about how much sun you want through the glass, not how well it insulates.
What is a surface 4 Low-E coating?
A hard, durable Low-E applied to the room-side face of the inner pane, which is surface 4 on a double-pane unit. Cardinal's LoE-i89 is the common one; Andersen calls it HeatLock and Marvin calls it ERS. It reflects room heat back into the room and lowers the U-factor. The room-side glass runs slightly cooler as a result, so manufacturers suggest pairing it with good humidity control.
Is Andersen SmartSun or PassiveSun better for Minnesota?
PassiveSun is Andersen's high-solar-gain glass and suits south windows that get winter sun. SmartSun is the low-gain option that blocks about 95 percent of UV and suits west windows and rooms that overheat. Andersen's standard Low-E4 sits between them. Many Minnesota houses do best with PassiveSun on the south, SmartSun on the west and HeatLock added on the north.
Can you mix Low-E coatings on the same house?
Yes. Coatings are ordered per window, and mixing by elevation is how a cold-climate order should be written. Keep the same coating within one wall or one view, because high- and low-gain glass have a slightly different tint side by side. Check that each unit still meets the ENERGY STAR Northern criteria if the label matters for a rebate.
Does a high-solar-gain Low-E coating cause fading?
It blocks less UV than a low-gain coating, so floors and fabrics in a sunny south room will fade faster than behind LoE-366 or SmartSun. If the room has hardwood, artwork or furniture you care about and no overhang, the moderate-gain option is the compromise: still useful winter sun, more UV blocked.
