Heat Transfer Coefficient Calculator
This heat transfer coefficient calculator will help you determine the overall heat transfer coefficient or film coefficient. This parameter is vital to most heat transfer calculations and insulation, especially for building walls. For instance, if a designer wishes to reduce the heat transfer via a building wall or heat exchanger, they add several layers of insulation.
This tool uses the heat transfer coefficient equation while giving you the option of adding up to 10 layers to your wall and returning the thermal resistance and overall heat transfer coefficient for the stacked structure.
The heat transfer coefficient is a function of wall thickness, thermal conductivity, and the contact area of the wall. The tool considers conduction through each layer of the wall while performing the calculations. Different types of convection and flow geometries also exist using the Nusselt number. Read on to understand what the heat transfer coefficient is and how to use the heat transfer coefficient formula.
🙋 If you are unsure about what thermal conductivity is or how to calculate it, you can look at our thermal conductivity calculator to learn more about this topic!
Overall heat transfer coefficient — Concept of thermal resistance
What is the heat transfer coefficient? It is a measure of how well a wall or structure conducts heat. In other words, it is the ratio of heat transfer through a unit area and temperature difference. This ratio is the combined value for all the layers in the structure. It is measured in W/(m²·K) or BTU/(h·°F·ft²).
The heat transfer coefficient formula considering n layers in a structure is:
1 ÷ Ut = (1 ÷ A) · Σi=1n (Li ÷ ki)
- Ut — Heat transfer coefficient (conductance);
- A — Contact area;
- L — Thickness of the nth layer; and
- k — Thermal conductivity of the layer material.
💡 Did you know? The lower the value of the heat transfer coefficient, the better the insulation provided by the structure, and vice versa.
How to calculate the heat transfer coefficient or film coefficient
For a wall made of stacked layers, heat travels by conduction through each layer in series. Each layer adds its own thermal resistance, defined per unit area as L / k. The resistances add up, so:
- Per-area thermal resistance (R-value): Rvalue = Σ (Li / ki), measured in m²·K/W (or ft²·hr·°F/BTU).
- Overall heat transfer coefficient (U-value): U = 1 / Rvalue, measured in W/(m²·K) (or BTU/(hr·ft²·°F)). The lower the U-value, the better the insulation.
- Total thermal resistance: Rtotal = Rvalue / A, measured in K/W (or hr·°F/BTU).
- Conductance (Ut = U·A): the inverse of the total thermal resistance, measured in W/K (or BTU/(hr·°F)).
- Heat flow rate (optional): if you enter a temperature difference ΔT, the wall transmits Q = U · A · ΔT, measured in W (or BTU/hr).
Unit Systems
This calculator supports two unit systems:
- Metric (SI) — thickness in m, conductivity in W/(m·K), area in m², temperature difference in K. The U-value is reported in W/(m²·K).
- Imperial / US customary — thickness in ft, conductivity in BTU/(hr·ft·°F), area in ft², temperature difference in °F. The U-value is reported in BTU/(hr·ft²·°F).
Typical thermal conductivity values (metric)
- Copper ≈ 401 W/(m·K), Aluminum ≈ 237 W/(m·K), Iron ≈ 80.2 W/(m·K) — excellent conductors.
- Concrete ≈ 1.7 W/(m·K), Glass ≈ 0.8 W/(m·K), Brick ≈ 0.72 W/(m·K).
- Wood ≈ 0.12 W/(m·K), Fiberglass ≈ 0.04 W/(m·K), Styrofoam ≈ 0.033 W/(m·K) — good insulators.
Use the per-layer material preset menu in the calculator to auto-fill these values.
Example: Using the heat transfer coefficient calculator
Consider a 10 m² wall built from two layers:
- Layer 1 — brick, 0.1 m thick, k = 0.72 W/(m·K) → L/k = 0.1389 m²·K/W
- Layer 2 — fiberglass insulation, 0.05 m thick, k = 0.04 W/(m·K) → L/k = 1.25 m²·K/W
Then:
- R-value = 0.1389 + 1.25 = 1.3889 m²·K/W
- U-value = 1 / 1.3889 = 0.72 W/(m²·K)
- Total thermal resistance R = 1.3889 / 10 = 0.1389 K/W
- Conductance Ut = A / Σ(L/k) = 10 / 1.3889 = 7.2 W/K
- With ΔT = 20 K, heat flow rate Q = 7.2 × 20 = 144 W
Notice how the thin fiberglass layer dominates the resistance — that is the whole point of insulation.
FAQs
- What is the overall heat transfer coefficient?
- It is the combined measure of how well a multi-layer structure conducts heat: the ratio of heat transferred to the product of area and temperature difference. A lower value means better insulation.
- What is the difference between the U-value and the R-value?
- The U-value (W/(m²·K)) is the overall heat transfer coefficient — the ease with which heat passes. The R-value (m²·K/W) is the per-area thermal resistance — the resistance to heat flow. They are reciprocals: U = 1 / R-value.
- How do I lower the heat transfer coefficient?
- Add more insulation: increase the thickness L of low-conductivity layers, or use materials with a lower thermal conductivity k. Both raise the L/k ratio and thus the thermal resistance.
- What is the film coefficient?
- The film (or convection) coefficient describes heat transfer between a surface and a moving fluid. For a stacked solid wall analyzed by conduction, the overall heat transfer coefficient plays the equivalent combined role for the whole structure.
- How many layers can I add?
- You can stack up to 10 layers. Each layer contributes its own L/k thermal resistance, and the calculator sums them to find the overall coefficient.