U
U-factor & ratings
How the U-factor measures heat transfer, how it differs from R-value, and how to read an NFRC label before buying.
Read →Residential Glazing Reference
Windows that hold heat through a Canadian winter.
A plain-language reference on glazing performance, U-factor ratings, and frame materials chosen for cold climates — from the Prairies to the Atlantic coast.
A sealed double-glazed unit: two panes separated by a spacer and an insulating gas-filled cavity. Photo: Wikimedia Commons.
Core Topics
Where window heat loss actually happens
In a heated home, glazing is usually the weakest thermal link in the wall. These three areas decide how a window performs once outdoor temperatures drop well below freezing.
Cross-section of a sealed unit showing panes, spacer, and cavity. Diagram: Wikimedia Commons.
How To Read A Window
A label, not a guess
In Canada, residential window performance is commonly certified to the rating system administered by the National Fenestration Rating Council and referenced by ENERGY STAR Canada. The values on the label let you compare products on the same basis.
The two numbers most relevant to winter comfort are the U-factor (heat loss) and the air-leakage rating. A lower U-factor means less heat escapes through the assembly.
At A Glance
Glazing types compared
A general comparison of common residential glazing assemblies. Exact figures depend on the specific product, frame, and coatings, so always confirm against the rated label.
| Assembly | Typical layers | Cavity fill | Relative winter performance |
|---|---|---|---|
| Single pane | 1 | None | Lowest; rarely used in new Canadian builds |
| Double, clear | 2 | Air | Baseline modern minimum |
| Double, low-e + argon | 2 | Argon | Strong; common ENERGY STAR choice |
| Triple, low-e + argon/krypton | 3 | Argon or krypton | Highest; favoured in the coldest zones |
Latest Reading
Articles
Understanding window U-factor ratings
What the U-factor measures, how it relates to comfort, and how to read an NFRC label.
Read article →Choosing frame materials for cold climates
How vinyl, fibreglass, wood, and aluminium handle deep cold and condensation.
Read article →Why a third pane matters in winter
The role of additional panes, low-e coatings, and inert gas fills in long sub-zero seasons.
Read article →Contact
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General reference inquiries only. For product specifications, consult the manufacturer's certified documentation.