Thermal Resistance Calculator - R-Value
Calculate thermal resistance (R-value and U-value) for composite walls with multiple layers.
Introduction
Calculate the overall heat transfer coefficient (U-value) for a composite wall assembly with up to 3 material layers plus convection resistances on both sides. U-value is the reciprocal of total R-value.
How This Calculator Works
U = 1/R_total. R_total = R_inside + Σ(L_i/k_i) + R_outside. Three material layers provided: L in m, k in W/mK. h in W/m²K.
Step-by-step process:
- Enter your input values in the calculator above
- The engine converts all inputs to SI base units (meters, kg, Pa)
- The formula is evaluated:
1 / (1/h_in + l1/k1 + l2/k2 + l3/k3 + 1/h_out) - Result is formatted with the appropriate unit and precision
Calculation Example
Unit Conversion for Thermal Resistance
**R-value units**
- 1 m²·K/W = 5.678 ft²·°F·hr/BTU
- 1 ft²·°F·hr/BTU = 0.1761 m²·K/W
**U-value units**
- 1 W/m²·K = 0.1761 BTU/hr·ft²·°F
- 1 BTU/hr·ft²·°F = 5.678 W/m²·K
**Conductivity units**
- 1 W/m·K = 0.578 BTU/hr·ft·°F
R = thickness / k for a single layer; U = 1/R_total for the assembly. Convert all layers to one consistent unit system before summing R-values.
Engineering Applications
- •Building insulation design
- •HVAC load calculation
- •Energy code compliance
- •Wall/roof assembly rating
Frequently Asked Questions
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