SHGC Explained: The Most Important Window Spec Quebec Buyers Skip

Most Quebec homeowners can recite their window’s U-factor but have never heard of its SHGC — and yet that second number decides how comfortable your home feels every sunny afternoon. It is the spec that quietly governs summer overheating, and it is the one most quotes leave blank.

What is SHGC?

SHGC stands for Solar Heat Gain Coefficient. It is a single number between 0 and 1 that tells you what fraction of the solar energy striking a window passes through and becomes heat inside the room. A window with a SHGC of 0.30 admits 30% of the available solar heat; one rated 0.60 admits 60%. The lower the number, the less the sun warms the space behind the glass.

Crucially, SHGC measures the whole window, not just the glass — it accounts for the frame, the spacer, and how much glass area the unit has. That is why two windows with the same coated glass can post slightly different SHGC values depending on their frame and proportions. When you compare quotes, make sure you are comparing the whole-window number, which is what the NRCan and ENERGY STAR labels report.

Lower SHGC is good news in any room that tends to overheat — west-facing living rooms, sunrooms, top-floor bedrooms. But it is not a number to minimize blindly everywhere, because in a Quebec winter a bit of free solar heat through a south window is genuinely useful. The art is choosing the right SHGC for each exposure rather than one value for the whole house.

U-Factor vs SHGC: Different Jobs

U-factor and SHGC are often confused, but they describe two completely different physical events. U-factor measures how readily heat conducts through the window when there is a temperature difference and no sun — think of a frigid −20°C January night, when a low U-factor keeps your heat indoors. SHGC measures how much radiant heat the sun pushes through the glass on a bright day, regardless of the outdoor temperature.

Quebec is one of the few climates where both numbers genuinely matter, because the province swings from brutal winters to increasingly hot, humid summers within the same year. A window optimized only for U-factor can still cook a west-facing room in July; a window optimized only for SHGC can bleed heat all winter. You want both handled well, and modern glazing lets you tune them largely independently.

A practical way to remember it: U-factor is your winter heating spec, SHGC is your summer cooling spec. If a salesperson talks only about U-factor, they are showing you half the picture. Ask for both numbers in writing, per window package, before you sign anything.

Choose Different SHGC by Window Orientation

There is no single “best” SHGC for a Quebec home — the right value depends entirely on which way the window faces and how the sun tracks across it through the day. The sun rises in the north-east in summer, swings high across the south at midday, and sets in the north-west, hammering west walls late in the afternoon. Matching glass to exposure is how you get free winter warmth where you want it and reject summer heat where you do not.

Use the ranges below as a starting framework for the Montreal region. Your installer can fine-tune them based on shading, overhangs, and how each room is used — a west bedroom you sleep in matters more than a west garage.

• North-facing: SHGC 0.40–0.50 — these windows get almost no direct summer sun, so any heat gain is welcome in winter and harmless in summer.
• East-facing: SHGC 0.30–0.40 — morning sun is gentle and the room cools off by afternoon, so a moderate value works well.
• South-facing: SHGC 0.35–0.45 — a higher value captures valuable passive winter heat, while a summer overhang blocks the high midday sun.
• West-facing: SHGC 0.25–0.30 — the low, intense afternoon sun is the harshest of all, so prioritize the lowest practical value here.

ENERGY STAR, Zone D, and Reading the Label

In Canada, windows are rated for one of four climate zones, and the Montreal region falls in Zone D — the second-coldest band. ENERGY STAR certification for Zone D requires a strong U-factor (an Energy Rating, or ER, at or above the threshold) and permits an SHGC of up to about 0.32 for high-performance certification. That ceiling exists precisely because the program recognizes summer overheating is now part of the Quebec equation.

When you look at an NRCan or NFRC label on a window sticker, you will see both the U-factor and the SHGC printed side by side, along with Visible Transmittance (VT), which tells you how much daylight comes through. A good summer-comfort window keeps SHGC low while keeping VT reasonably high — that is the signature of a quality solar-control coating that blocks heat without darkening the room.

Chasing ENERGY STAR Zone D certification is also the gateway to rebates: Rénoclimat and federal programs such as Canada Greener Homes require certified units. So the same label that guarantees balanced winter-and-summer performance is also the one that unlocks up to roughly $150 per rough opening provincially and historically up to $5,000 federally.

How Triple-Pane and Coatings Lower SHGC

Two design choices drive SHGC down: the Low-E coating and the number of panes. A solar-control Low-E coating reflects infrared heat back outside, and adding a second coating — one per air cavity in a triple-pane unit — compounds the effect. This is why a well-built triple-pane window almost always posts a lower SHGC than a comparable double-pane, on top of its lower U-factor.

The gas fill plays a supporting role. Argon or krypton between the panes slows conductive heat transfer, which mainly improves the U-factor, but the combination of multiple Low-E layers and dense gas fill is what lets a 2026 triple-pane unit hit a low SHGC and a low U-factor at the same time — the holy grail for a four-season climate like ours.

There is a trade-off to watch: pushing SHGC very low also reduces VT, so an aggressively coated unit can look slightly grey or dim. Reputable manufacturers offer several glass packages so you can pick the sweet spot — low enough SHGC for comfort, high enough VT for bright rooms. Discuss this balance rather than accepting a single default.

• Solar-control Low-E is the primary lever for lowering SHGC
• A second Low-E coating in a triple-pane unit pushes SHGC lower still
• Argon or krypton fill mainly improves U-factor, complementing the coating
• Watch Visible Transmittance (VT) so a low-SHGC window does not look dim

How to Specify SHGC on Your Quote

Here is the single most valuable habit when shopping for windows in Quebec: insist that every quote lists the SHGC alongside the U-factor for each glass package, broken down by orientation if the installer offers per-window glass. Most installers default to one glass package across the entire home because it simplifies their ordering — convenient for them, but not optimal for you.

The cost difference between a single-package job and an orientation-tuned one is usually marginal, often just a few hundred dollars across a full house, because you are reallocating glass types rather than buying more expensive windows everywhere. The comfort difference, by contrast, is something you feel every sunny afternoon for the next 25 years. It is one of the best value-per-dollar decisions in the whole project.

When you receive a quote, look for three numbers per window: U-factor, SHGC, and VT. If any are missing, ask. A confident, experienced installer will have them ready and will be able to explain why they chose a given SHGC for your west wall versus your north wall.

Get an Orientation-Tuned Quote

We build every quote around your home’s actual exposures, specifying U-factor, SHGC, and VT per opening and explaining the reasoning in plain language. You see exactly which glass goes on the west wall and why, and how each choice ties back to ENERGY STAR Zone D and your rebate eligibility.

If a previous quote never mentioned SHGC, that alone is a reason to get a second opinion. Request a free, orientation-tuned estimate and see how much summer comfort you can gain for very little added cost.

Frequently Asked Questions