Thermal Conductivity Heat Flow Calculator
Calculate heat flow rate through a material using thermal conductivity, thickness, area, and temperature difference.
Useful for insulation and building design.
Heat Flow Rate
Thermal Conductivity and Heat Flow
Thermal conductivity (k) measures how well a material conducts heat. A low k-value means the material is a good insulator. A high k-value means the material conducts heat readily.
Fourier’s Law of Heat Conduction
The rate of heat flow through a flat material is:
Q = k × A × ΔT ÷ d
Where:
- Q = Heat flow rate (Watts or BTU/hr)
- k = Thermal conductivity (W/m·K)
- A = Cross-sectional area (m²)
- ΔT = Temperature difference across the material (°C or K)
- d = Thickness of the material (m)
Thermal Conductivity of Common Materials
| Material | k (W/m·K) | Notes |
|---|---|---|
| Air (still) | 0.025 | Best natural insulator |
| Aerogel | 0.015 | Best solid insulator |
| Mineral wool | 0.030–0.045 | Common building insulation |
| EPS (Styrofoam) | 0.033–0.040 | Foam board insulation |
| Wood (pine) | 0.12 | Structural timber |
| Brick | 0.60–1.0 | Masonry walls |
| Concrete | 1.0–1.5 | Structural concrete |
| Glass | 0.96 | Windows |
| Steel | 50 | Structural steel |
| Aluminum | 205 | Heat sinks |
| Copper | 385 | Electrical wiring |
Relationship Between k, R-Value, and U-Value
R-value (m²·K/W) = d ÷ k
U-value (W/m²·K) = k ÷ d = 1 ÷ R-value
Higher R-value = better insulation. Lower U-value = better insulation.
Practical Example
A 100 mm (0.1 m) thick concrete wall (k = 1.0 W/m·K), area 10 m², with indoor 20°C and outdoor −5°C:
- ΔT = 25°C
- Q = 1.0 × 10 × 25 ÷ 0.1 = 2,500 Watts of heat loss
Compare to 100 mm of mineral wool (k = 0.035):
- Q = 0.035 × 10 × 25 ÷ 0.1 = 87.5 Watts — 28× less heat loss