Conversion Formula
U-factor (BTU/hr·ft²·°F) = U (W/m²·K) x 0.17611
RSI (m²·K/W) = 1 / U (W/m²·K)
R-value (ft²·°F·hr/BTU) = 1 / U-factor
Conversion factor: 1 W/m²·K = 0.17611 BTU/hr·ft²·°F
Window U-Value Reference Table
| Window Type | U-Value (W/m²·K) | U-Factor (BTU/hr·ft²·°F) | RSI | Notes |
|---|---|---|---|---|
| Single pane, aluminum frame | 5.8 - 6.2 | 1.02 - 1.09 | 0.16 - 0.17 | Legacy / commercial storefront |
| Single pane, wood/vinyl frame | 4.5 - 5.3 | 0.79 - 0.93 | 0.19 - 0.22 | Older residential |
| Double pane, aluminum frame | 3.0 - 3.7 | 0.53 - 0.65 | 0.27 - 0.33 | Thermal break frame required |
| Double pane, air-filled | 2.5 - 3.0 | 0.44 - 0.53 | 0.33 - 0.40 | Basic double glazing |
| Double pane, LoE coating, argon | 1.4 - 2.0 | 0.25 - 0.35 | 0.50 - 0.71 | Common quality Canadian window |
| Triple pane, LoE, argon fill | 0.8 - 1.4 | 0.14 - 0.25 | 0.71 - 1.25 | Cold-climate / northern Canada |
| Triple pane, LoE, krypton fill | 0.6 - 1.0 | 0.11 - 0.18 | 1.00 - 1.67 | High performance; premium cost |
| ENERGY STAR Canada (zone 2) | max 1.60 | max 0.282 | min 0.63 | Zones 3-4 requirement |
| ENERGY STAR Canada (zone 3) | max 1.40 | max 0.246 | min 0.71 | Most Canadian markets |
| ENERGY STAR Canada (zone 4) | max 1.20 | max 0.211 | min 0.83 | Coldest Canadian climate zone |
| Passive House window | max 0.80 | max 0.141 | min 1.25 | Passive House Institut standard |
Canadian NBC Maximum Window U-Values (Part 9)
| Climate Zone | Max U-Value (W/m²·K) | Max U-Factor (BTU/hr·ft²·°F) | Key Cities |
|---|---|---|---|
| Zone 4 (mildest) | 2.00 | 0.352 | Victoria, Vancouver coast |
| Zone 5 | 1.80 | 0.317 | Vancouver (inland), Kelowna |
| Zone 6 | 1.60 | 0.282 | Toronto, Ottawa, Montreal |
| Zone 7A | 1.40 | 0.246 | Calgary, Edmonton, Winnipeg |
| Zone 7B | 1.40 | 0.246 | Northern Prairies, northern ON/QC |
| Zone 8 (coldest) | 1.40 | 0.246 | Yellowknife, northern territories |
NBC 2020 Part 9 values for fenestration. These are maximum U-values -- lower is better. Provincial codes and municipal building authorities may require stricter values. EnerGuide and ENERGY STAR Canada programs require lower U-values than the NBC minimum.
Typical Wall and Roof Assembly U-Values
| Assembly | U-Value (W/m²·K) | U-Factor (BTU/hr·ft²·°F) | RSI (m²·K/W) | R-Value |
|---|---|---|---|---|
| 2x4 stud wall, R-12 batt, no exterior insulation | 0.47 | 0.083 | 2.11 | R-12 |
| 2x6 stud wall, R-19 batt (effective with bridging) | 0.33 | 0.058 | 3.03 | R-17 |
| 2x6 wall + 1-in XPS exterior (effective) | 0.24 | 0.042 | 4.23 | R-24 |
| 2x6 wall + 2-in mineral wool exterior (effective) | 0.18 | 0.032 | 5.56 | R-32 |
| Attic, R-40 blown cellulose | 0.14 | 0.025 | 7.04 | R-40 |
| Attic, R-49 blown fiberglass | 0.12 | 0.021 | 8.63 | R-49 |
| Flat roof, R-30 polyiso (effective) | 0.19 | 0.033 | 5.28 | R-30 |
| Slab-on-grade (uninsulated) | 0.57 | 0.100 | 1.76 | R-10 |
How to Use the U-Value Converter
Type a metric U-value (W/m²·K) from a Canadian specification or a Imperial U-factor from a US window label or NFRC rating. The other value converts instantly, along with RSI and R-value equivalents -- useful for cross-referencing window specs against insulation values.
Load common window types with one click: single pane, standard double-pane LoE argon, the NBC maximum for cold-climate zones (1.4 W/m²·K), triple pane, and Passive House performance level. The context band immediately tells you what performance tier your value falls in and whether it meets NBC or ENERGY STAR Canada requirements.
The NBC maximum U-value table shows the code limit for each Canadian climate zone in both W/m²·K and BTU/hr·ft²·°F. Compare your converted value against the requirement for your project city to confirm code compliance before specifying or ordering windows.
Use the converted U-value (W/m²·K) with window area (m²) and design temperature difference to calculate window heat loss: Q (W) = U x A x DeltaT. Feed this into the Window Heat Loss Calculator for a complete window-by-window analysis, or use the Heat Load Calculator for a full building envelope assessment.
U-Value in Canadian HVAC -- Complete Guide
U-value (thermal transmittance) quantifies how readily heat flows through a building assembly per unit area per degree of temperature difference. It's the inverse of R-value and RSI: lower U-value means better thermal performance. Canadian codes and engineering use W/m²·K; window labels and US specifications use BTU/hr·ft²·°F. Converting between these is a routine task in Canadian window specification and heat loss calculation work.
The Conversion Factor: 0.17611
To convert metric U-value to Imperial U-factor: multiply by 0.17611. To convert the other way: divide by 0.17611 (or multiply by 5.678). A window with U = 1.4 W/m²·K has U-factor = 1.4 x 0.17611 = 0.246 BTU/hr·ft²·°F. Note that 0.17611 and 5.678 are the same factor used for R-value to RSI -- because U and R are inverses in the same unit system. The R-Value / RSI Converter handles the inverse conversion.
Windows and U-Value in Canadian Practice
Windows are the weakest thermal link in most Canadian building envelopes. A well-insulated 2x6 wall might achieve an effective RSI of 3.5 (U = 0.29 W/m²·K). A standard double-pane window might have U = 2.8 W/m²·K -- nearly 10 times higher heat loss per unit area. This is why window area, orientation, and U-value have a disproportionate impact on heating loads in Canadian homes. Reducing window U-value from 2.0 to 1.4 W/m²·K on a 30 m² window area with a 40 K design DeltaT reduces peak window heat loss by (2.0 - 1.4) x 30 x 40 = 720 W -- nearly a quarter of a ton of heating capacity.
ENERGY STAR Canada vs. NBC Requirements
The NBC sets minimum code compliance thresholds. ENERGY STAR Canada certification, administered by NRCan, sets higher performance targets. ENERGY STAR Canada Zone 3 (covering most Canadian markets including Calgary, Edmonton, and Winnipeg) requires windows with maximum U = 1.40 W/m²·K (U-factor 0.246) -- the same as the NBC maximum for zones 7A and 7B. Zone 4 (the coldest ENERGY STAR zone) requires U = 1.20 W/m²·K. Many builders in cold climates specify triple-pane windows with U values of 0.8 to 1.2 W/m²·K for better long-term energy performance and comfort near glazing.
U-Value vs. SHGC -- Both Matter
A window's thermal performance involves two key metrics: U-value (heat loss by conduction) and SHGC (Solar Heat Gain Coefficient -- solar heat gain). In Canadian cold climates, south-facing windows with lower U-value and higher SHGC (0.40 to 0.60) can provide net positive energy contribution during heating season through passive solar gain. North-facing windows should have low SHGC. ENERGY STAR Canada specifies both U-value and minimum SHGC requirements by zone. Specifying windows without considering both metrics risks either over-shading or under-insulating critical glazing areas.
U-Value in Heat Loss Calculations
Window heat loss at design conditions: Q (W) = U (W/m²·K) x A (m²) x DeltaT (K). A 2 m² window with U = 1.4 W/m²·K at Calgary's design DeltaT of 50 K (inside 21°C, outside -29°C) loses 1.4 x 2 x 50 = 140 W at peak conditions. That same calculation in Imperial: U-factor 0.246 BTU/hr·ft²·°F x 21.5 ft² x 90°F DeltaT = 476 BTU/hr = 139 W. Use the Window Heat Loss Calculator for full window-by-window analysis including frame area corrections and orientation factors.
Frequently Asked Questions
Multiply W/m²·K by 0.17611 to get BTU/hr·ft²·°F. To go the other way, divide by 0.17611 (or multiply by 5.678). A common Canadian window at U = 1.4 W/m²·K equals U-factor 0.246 BTU/hr·ft²·°F. A Passive House window at U = 0.8 W/m²·K equals U-factor 0.141. Canadian code documents specify W/m²·K; NFRC labels on North American windows use BTU/hr·ft²·°F.
NBC 2020 Part 9 sets maximums by climate zone. For zones 7 and 8 (Calgary, Edmonton, Winnipeg, most of northern Canada), the maximum is U = 1.40 W/m²·K (U-factor 0.246). For zone 6 (Toronto, Ottawa, Montreal), the maximum is U = 1.60 W/m²·K (0.282). ENERGY STAR Canada Zone 3 (most Canadian markets) matches the zone 7 maximum at 1.40 W/m²·K. Better windows -- triple pane with LoE coatings and argon or krypton fill -- commonly achieve 0.8 to 1.2 W/m²·K.
U-value and R-value are inverses: U = 1/R in consistent units. High R-value means low U-value, meaning better insulation. Windows are rated by U-value because their low thermal resistance makes it more intuitive -- U = 1.4 W/m²·K is easier to compare than RSI 0.71. Wall assemblies are rated by R-value because their high resistance makes RSI 3.5 or R-20 more intuitive than U = 0.29 W/m²·K. The R-Value / RSI Converter handles the insulation side of these calculations.
SHGC (Solar Heat Gain Coefficient) measures the fraction of solar radiation that passes through a window, from 0 (none) to 1 (all). It's separate from U-value, which measures conductive heat loss. In Canadian cold climates, south-facing windows benefit from higher SHGC (0.40 to 0.60) to capture free solar heat, reducing heating loads. North-facing windows should have low SHGC to minimize summer gains without useful winter solar contribution. ENERGY STAR Canada specifies both U-value maximums and SHGC minimums by zone -- you need both numbers to specify a compliant window.