Composite Wall Assembly
Calculation Results
Total Thermal Resistance (R-value)
0.00 K·m²/W
Overall Heat Transfer Coefficient (U-value)
0.00 W/m²·K
R-Value Contribution by Material Layer
This chart dynamically shows the thermal resistance of each layer to help you visualize their contribution to the total R-value.
Fundamentals and Data
Dive into the core concepts and find a searchable table of thermal properties for common materials.
What is Thermal Resistance?
Thermal resistance (R-value) is a measure of a material's ability to resist the flow of heat. A higher R-value indicates better insulation. It's crucial in building design and thermal management to reduce energy consumption for heating and cooling.
Key Concepts
- Thermal Conductivity (k): An intrinsic property of a material that measures its ability to conduct heat. Low k-values mean the material is a poor conductor (a good insulator). Units: $W/m·K$.
- Thermal Resistance (R): The resistance of a specific thickness of a material. Calculated as Thickness / Conductivity. Units: $K·m²/W$.
- Overall Heat Transfer Coefficient (U): The reciprocal of the total R-value ($U = 1 / R_{total}$). It measures how well a building element conducts heat. A lower U-value is better. Units: $W/m²·K$.
Core Calculation Formulas
R = L / k
Where R is thermal resistance, L is the material thickness (in meters), and k is the thermal conductivity.
Rtotal = R₁ + R₂ + ... + Rn
The total resistance of a composite wall is the sum of the individual resistances of each layer.
U = 1 / Rtotal
The U-value is the reciprocal of the total R-value.
How to Use the Calculator
- Set Area: Start by entering the total surface area of your wall in the Results panel.
- Add Layers: Click the "+ Add Material Layer" button to add the first layer of your assembly.
- Select Material: Choose a material for the layer from the dropdown menu. The material's k-value is automatically used.
- Enter Thickness: Input the thickness of the material layer in millimeters.
- Add More Layers: Continue adding layers to build your complete wall assembly, from outside to inside.
- Review Results: The Total R-value and U-value will update automatically as you make changes.
Common Material Thermal Properties
This table provides thermal conductivity (k-value) data for common building materials to serve as a reference.
| Material | Thermal Conductivity (k) [$W/m·K$] |
|---|
Design Checks for Thermal Resistance Calculator
thermal resistance calculator design checks - Use these checks before trusting the calculator result in a PCB, repair, or reverse engineering workflow.
Junction temperature is Tj = Ta + P*thetaJA. For a heatsink path, add thetaJC + thetaCS + thetaSA and compare the result with maximum junction rating, copper area, airflow, and power derating over ambient temperature.
- Confirm the formula assumptions against the real circuit topology, component tolerances, and parasitic PCB effects.
- Check operating limits such as voltage, current, bandwidth, temperature rise, or safety margin before selecting parts.
- When a measured board disagrees with the calculator, inspect the surrounding components and test points before changing the design.
Keep the calculation result with the schematic revision, measured values, and component datasheets.
