Window U-value Calculator
Whole-window U-value per EN ISO 10077-1 · Frame / glass / spacer comparison
Uf = 1.2 W/m²K · 58 mm
Ug = 0.6 W/m²K · 40 mm
Ψg = 0.04 W/mK
Sash: 58 mm
Width
×Height
EN ISO 10077-1: Uw = (Ag·Ug + Af·Uf + lg·Ψg) / (Ag + Af)
IECC/ASHRAE 90.1 (US) · CSA A440/NEB (CA) · EPBD (EU) · GB 50189/GB 50176 (CN)
IECC/ASHRAE 90.1 (US) · CSA A440/NEB (CA) · EPBD (EU) · GB 50189/GB 50176 (CN)
Whole-window Uw0.90W/m²KPassive / near-zero energy
Calculation breakdown
- Glass area (Ag)
- 1.13 m²
- Frame area (Af)
- 0.55 m²
- Glass fraction
- 67%
- Glass perimeter (lg)
- 4.27 m
- Frame Uf
- 1.2 W/m²K
- Glass Ug
- 0.6 W/m²K
- Spacer Ψg
- 0.04 W/mK
vs aluminium (no thermal break)
Thermal performance is 44% better than aluminium without thermal break (U_w = 1.62 W/m²K).
Code compliance
🇨🇳 China Severe cold (Harbin)≤ 1.50 ✓
🇨🇳 China Cold (Beijing)≤ 2.00 ✓
🇨🇳 China Hot summer / cold winter (Shanghai)≤ 2.30 ✓
🇨🇳 China Hot summer / warm winter (Guangzhou)≤ 3.00 ✓
🇪🇺 EU Passive House≤ 0.80
🇪🇺 EU Near-zero energy≤ 1.30 ✓
🇺🇸 US ENERGY STAR Northern≤ 1.70 ✓
🇨🇦 Canada Zone A (coldest)≤ 1.20 ✓
Frame U comparison Uf
Frame U-values used in this calculator. FRP frames have inherently low conductivity — no thermal break required.
| Frame system | Uf (W/m²K) | Depth (mm) | Face width (mm) | Thermal break needed? |
|---|---|---|---|---|
| FRP 65系列 (65mm, 2腔) | 1.4 | 65 | 54 | No — inherently insulating |
| FRP 70系列 (70mm, 3腔) | 1.2 | 70 | 58 | No — inherently insulating |
| FRP 80系列 (80mm, 3腔) | 1 | 80 | 65 | No — inherently insulating |
| FRP 90系列 (90mm, 3腔) | 0.85 | 90 | 72 | No — inherently insulating |
| 铝合金（无隔热条） | 5.9 | 65 | 50 | No — but very high conductance |
| 铝合金（PA隔热条） | 3.2 | 70 | 55 | Yes — PA thermal break |
| PVC多腔型 | 1.5 | 70 | 62 | No — but lower stiffness |
| PVC钢衬型 | 1.8 | 70 | 65 | Steel liner creates thermal bridge |
| 木材（软木, 68mm） | 1.4 | 75 | 65 | No — inherently insulating |
International window U-value requirements
Maximum allowable whole-window U-values in major building energy codes. Residential unless noted.
| Region | Standard | Climate zone / grade | Max U (W/m²K) | Notes |
|---|---|---|---|---|
| China | GB 50189-2015 | Severe cold (Harbin) | ≤ 1.50 | Public buildings; residential per GB 50176 |
| China | GB 50189-2015 | Cold (Beijing) | ≤ 2.00 | Public buildings |
| China | GB 50189-2015 | Hot summer / cold winter (Shanghai) | ≤ 2.30 | Public buildings; SHGC also limited |
| China | GB 50189-2015 | Hot summer / warm winter (Guangzhou) | ≤ 3.00 | Public buildings; SHGC dominant |
| China | GB 50176-2016 | Residential (severe cold) | ≤ 1.50 | Civil building thermal design code |
| China | GB 50176-2016 | Residential (cold) | ≤ 2.00 | Civil building thermal design code |
| China | GB/T 8484-2020 | Test method | — | Standard test for window thermal performance |
| EU | EN ISO 10077-1 | Passive House premium | ≤ 0.80 | PHI certified; installed |
| EU | EN ISO 10077-1 | Passive House classic | ≤ 0.85 | PHI certified |
| EU | EPBD 2024 | Near-zero energy (Central EU) | ≤ 1.30 | Member states vary |
| US | IECC 2024 | Zone 4 (New York) | ≤ 1.99 | NFRC tested |
| US | IECC 2024 | Zone 7-8 (Alaska) | ≤ 1.70 | Extreme cold |
| US | ENERGY STAR v7.0 | Northern | ≤ 1.70 | NFRC tested; strictest |
| Canada | CSA A440/NEB | Zone A (coldest) | ≤ 1.20 | Triple glazing typically required |
| Canada | CSA A440/NEB | Zone C (warmest) | ≤ 1.60 | Vancouver / southern Ontario |
Calculation note: This tool uses the simplified method of EN ISO 10077-1. NFRC (US/Canada) ratings require NFRC 100 simulation (THERM + WINDOW). Chinese GB compliance requires hot-box testing per GB/T 8484-2020. For reference only.