U-Value Calculator
Calculate thermal transmittance (U-Value) for building materials. Determine heat loss through walls, windows, roofs, and floors.
Step 1: Material Specifications
U-Value Formula
U-Value = 1 / (Rsi + R1 + R2 + … + Rse)
Where R = Thermal Resistance
Step 2: Calculation Options
Building Regulation Limits
Walls: Max 0.3 W/m²·K (UK)
Roofs: Max 0.2 W/m²·K (UK)
Windows: Max 2.0 W/m²·K (UK)
Floors: Max 0.25 W/m²·K (UK)
Thermal Transmittance Results
Total U-Value (Thermal Transmittance)
Building Material Comparison
| Material | Thickness | R-Value | U-Value |
|---|
U-Value Calculation Formula
U = 1 / (Rsi + R1 + R2 + … + Rse)
Where:
• U = Thermal transmittance (W/m²·K)
• R = Thermal resistance of each layer (m²·K/W)
• Rsi = Internal surface resistance
• Rse = External surface resistance
• R1, R2, … = Resistances of individual layers
To convert:
• Imperial U-Value = Metric U-Value × 0.1761
• R-Value = 1 / U-Value
Example Calculation
Example: Brick Wall with Insulation
Brickwork: R = 0.13 m²·K/W
Insulation: R = 2.5 m²·K/W
Plasterboard: R = 0.05 m²·K/W
Rsi = 0.13, Rse = 0.04
Calculation:
Total R = 0.13 + 2.5 + 0.05 + 0.13 + 0.04 = 2.85 m²·K/W
U-Value = 1 / 2.85 = 0.35 W/m²·K
Converted:
0.35 W/m²·K = 0.062 BTU/h·ft²·°F
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