Understanding Window Energy Ratings (ER): What the Sticker Actually Means
Too Long; Didn't Read
- ER Number: The overall "grade" of the window. Higher is better.
- U-Factor: How well it keeps heat IN. Lower is better.
- SHGC: How much sun heat lets IN. High = Free Winter Heat. Low = Summer Shade.
- Zone 3: Toronto needs specific ratings to qualify for rebates (even if the grant is gone, the standard remains).
Answer First: In Toronto (Zone 2/3), lock onto the ER (Energy Rating) number. An ER of 34 or higher is considered "High Efficiency." If you just look at "R-value," you're missing half the picture (solar gain).
The Sticker Decoded
Every certified window comes with a white sticker from key organizations like NFRC or CSA. It looks like a nutrition label for glass. Here is how to read it without a physics degree.
1. U-Factor (The Insulator)
- What it measures: Rate of heat loss.
- The Goal: Lower is Better.
- The Math: A U-Factor of 0.25 is better than 0.35.
- Analogy: Think of this like the R-value in your walls, but inverted. (R = 1 / U).
2. SHGC (Solar Heat Gain Coefficient)
- What it measures: How much solar radiation passes through the glass.
- The Scale: 0 to 1.
- The Strategy:
- South Facing: You want High SHGC (0.5+). Let the winter sun heat your home for free. Passive heating.
- West Facing: You want Low SHGC (0.2-). The afternoon sun is brutal and overheats your home. Block it.
3. ER (Energy Rating)
- What it measures: A specifically Canadian formula that balances U-Factor, SHGC, and Air Leakage.
- The Goal: Higher is Better.
- Passing Grade: ER 34+ is usually the benchmark for Energy Star "Most Efficient."
The "Triple Pane" Trap
You might think Triple Pane always has a better ER rating. Not necessarily. Triple pane glass adds an extra layer, which blocks more free solar heat.
- Scenario A: A double-pane window with High-Gain Low-E might have an ER of 38.
- Scenario B: A triple-pane window with heavy tints might have an ER of 32.
The Triple pane (Scenario B) will feel warmer to the touch at night (better U-factor), but the double pane (Scenario A) effectively lowers your heating bill more by letting in free sun during the day.
Which Coating Should You Choose?
When ordering, you get choices like "LoE 180" or "LoE 366".
| Coating Name | Best For... | SHGC | Visual |
|---|---|---|---|
| LoE 180 (Passive) | South/East windows. Free heating. | High | Very Clear |
| LoE 272 (Balanced) | All-around performance. | Medium | Neutral |
| LoE 366 (Sun Block) | West facing / Large walls of glass. | Low | Slight Tint |
Air Leakage: The Silent Killer
The ER rating accounts for Air Leakage (AL).
- A1: Drafty.
- A3: Standard.
- A3 High / Fixed: Airtight.
A fixed window (doesn't open) will always have a better rating than a slider, because seals eventually wear out, but solid glass doesn't.
Summary
- Look for Er >= 34.
- Ask for LoE 180 on the South.
- Ask for LoE 366 on the West.
Confused by the Numbers?
Send us a photo of your quote. We'll audit the Energy Ratings for free and tell you if you're getting the right glass for your exposure.