Window Heat Loss Calculator
Window Width (m)
Window Height (m)
U-value (W/m²·K)
Temperature Diff ΔT (°C)
U-value: Single glazing ≈ 5.7 · Double ≈ 2.8 · Triple ≈ 0.8
✓Heat Loss
Area (m²)
1.80
Heat Loss (W)
100.8
Annual Cost (est.)
$65.32
Annual Heating Energy (kWh)
435.5 kWh
A window heat loss calculator estimates the thermal energy lost through windows based on their U-value (thermal transmittance), area, and the temperature difference between inside and outside.
- 1Heat loss (W) = U-value × Area (m²) × ΔT (°C)
- 2U-value: single glazing ~5.8; double ~2.8; triple ~1.1 W/m²·K
- 3ΔT = Indoor temp − Outdoor temp (°C)
- 4Annual heat loss (kWh) = W × Hours/season / 1,000
5m² double glazing (U=2.8), 20°C inside, 0°C outside=Heat loss = 2.8 × 5 × 20 = 280W; annual (3,000 heating hours) = 840 kWh
| Glazing type | U-value (W/m²·K) | Energy rating (UK) |
|---|---|---|
| Single glazing | ~5.8 | F or below |
| Standard double | ~2.8 | C–D |
| A-rated double | ~1.6 | A |
| Triple glazing | ~0.8–1.1 | A+ |
References
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