💡 R = L/k (m²·K/W) | Q = ΔT / R × A (Watts) | k = Thermal Conductivity (W/m·K) | L = Thickness (m) | ΔT = Temperature difference (K/°C)
📖 How to Use This Thermal Resistance Calculator
1
Select what to calculate - Choose Thermal Resistance (R), Conductivity (k), Thickness (L), or Heat Flow (Q).
2
Enter known values - Input the required parameters based on your selection.
3
Click "Calculate" - Get the result with step-by-step solution.
🔥 Understanding Thermal Resistance (R-Value)
Thermal resistance (R-value) measures a material's ability to resist heat flow. The higher the R-value, the better the insulation. The formula is R = L/k, where L is thickness (meters) and k is thermal conductivity (W/m·K).
In building construction, R-value is crucial for energy efficiency. Higher R-value means less heat loss in winter and less heat gain in summer, reducing energy bills.
📊 Common Material Properties
Fiberglass insulation: k ≈ 0.04 W/m·K | R per inch ≈ 3.5-4.0
Spray foam (closed cell): k ≈ 0.026 W/m·K | R per inch ≈ 6.0
Mineral wool: k ≈ 0.038 W/m·K | R per inch ≈ 3.7
Brick: k ≈ 0.72 W/m·K | R per inch ≈ 0.2
Concrete: k ≈ 1.7 W/m·K | R per inch ≈ 0.08
Wood (softwood): k ≈ 0.12 W/m·K | R per inch ≈ 1.2
Glass: k ≈ 0.96 W/m·K | R per inch ≈ 0.15
Polyurethane foam: k ≈ 0.023 W/m·K | R per inch ≈ 6.5
🧮 Thermal Resistance Formulas
Thermal Resistance: R = L / k Thermal Conductivity: k = L / R Thickness: L = R × k Heat Flow: Q = (ΔT × A) / R
💡 Real-World Applications
Home Insulation: Selecting proper R-value for walls, attics, and floors
HVAC Systems: Duct insulation to prevent energy loss
Refrigeration: Insulating refrigerators and freezers
Electronics Cooling: Thermal management of components
Building Codes: Meeting energy efficiency requirements
❓ Frequently Asked Questions (FAQ)
What is the difference between R-value and U-value?
R-value measures resistance to heat flow (higher is better). U-value measures heat transmission (lower is better). They are inversely related: U = 1/R.
What R-value do I need for my home?
Recommendations vary by climate zone. Attics: R-30 to R-60, Walls: R-13 to R-21, Floors: R-19 to R-30. Check local building codes for specific requirements.
How does thermal conductivity affect insulation performance?
Lower thermal conductivity (k) means better insulation. For example, fiberglass (k≈0.04) is much better insulator than concrete (k≈1.7).
What is the thermal resistance of a multi-layer wall?
Total thermal resistance is the sum of individual layers: R_total = R₁ + R₂ + R₃ + ... Add air film resistances for complete wall assembly.
Why does thickness matter for insulation?
Thermal resistance increases linearly with thickness: double the thickness doubles the R-value. That's why thicker insulation performs better.
What are typical R-values per inch for common insulation?