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Overall Heat Transfer Coefficient Calculator

Find the overall heat transfer coefficient U for a plane wall sandwiched between two surface air films. The tool sums the series resistances 1/h1 + L/k + 1/h2 and inverts them, and can also return the heat flow if you supply an area and temperature difference.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the inside and outside film (convective) coefficients h1 and h2 in W/m2.K.
  2. Enter the wall thickness L in metres and its conductivity k in W/m.K.
  3. Optionally add the area A in m2 and temperature difference dT in kelvin to also compute the heat flow Q = U * A * dT.

How it works

For a plane wall with a convective film on each side, the resistances add in series: 1/U = 1/h1 + L/k + 1/h2, all expressed per unit area (m2.K/W). Inverting the total gives the overall heat transfer coefficient U in W/m2.K, which relates heat flux to the overall temperature difference by q = U * dT. Multiplying by area and the temperature difference gives the total heat flow, Q = U * A * dT.

Worked example

Worked example. For h1 = 10 W/m2.K, L = 0.2 m, k = 0.5 W/m.K and h2 = 25 W/m2.K: 1/U = 0.1 + 0.4 + 0.04 = 0.54 m2.K/W, so U = 1/0.54 = 1.85 W/m2.K. With A = 5 m2 and dT = 30 K, Q = 1.85 * 5 * 30 = 277.78 W.

Common mistakes

  • Forgetting one of the surface film resistances — both 1/h1 and 1/h2 must be included for a wall exposed to fluids on both sides.
  • Mixing per-area resistance (m2.K/W) with absolute resistance (K/W); U is defined per unit area.
  • Leaving out extra layers — each additional material adds its own L/k term to the series.

Frequently asked questions

How do I add more than one wall layer?

Add an L/k term for each layer inside the sum: 1/U = 1/h1 + L1/k1 + L2/k2 + ... + 1/h2. This tool covers a single wall layer with two films; extend the resistance sum manually for more layers.

What about fouling on heat exchanger surfaces?

Add fouling resistances (m2.K/W) as extra terms in the series before inverting. They increase 1/U and therefore reduce the overall coefficient.

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