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Convective Heat Transfer Calculator

Enter the coefficient, area and the two temperatures to find the convective heat transfer rate.

How it is calculated

The tool applies Newton's law of cooling: q = h × A × (Ts − T∞). h is the convective heat transfer coefficient in W/(m²·K), A is the surface area in m², Ts is the surface temperature and T∞ the temperature of the fluid far from the surface. The temperatures can both be in °C or both in K, because only their difference matters, but never one of each. The result is shown in watts with two decimals, in kilowatts with four decimals, and the temperature difference is listed as well. A positive value means heat flows from the surface into the fluid; if the fluid is hotter, the sign is negative. The tool does not check the signs of h or A, so enter positive values for them. Choosing h is the hard part and the tool does not estimate it.

Worked example

A panel with a surface area of 1.2 m² sits at 80 °C in air at 20 °C, with h = 25 W/(m²·K). The temperature difference is 80 − 20 = 60.00 degrees. Then q = 25 × 1.2 × 60 = 1,800.00 W. Divided by 1000 this is 1.8000 kW. If you swapped the temperatures (surface 20, fluid 80), the tool would return -1,800.00 W, meaning the heat flows into the surface instead.

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Common mistakes

  • Mixing a surface temperature in °C with a fluid temperature in K (or °F); the difference is then meaningless.
  • Using the wrong direction for the temperature difference: surface minus fluid is positive when the surface loses heat, and the reverse gives a negative rate.
  • Entering the area in cm² or mm² instead of m², which makes the power wrong by a factor of 10,000 or 1,000,000.
  • Using a coefficient from a table for a different fluid, flow speed or surface; h depends on all three, and the tool takes whatever you type as given.
  • Expecting the result to include radiation or conduction; only convection is calculated.

About this calculator

Convective heat transfer follows Newton's law of cooling: q = h·A·ΔT, where h is the convective heat transfer coefficient (W/m²·K) that depends on the fluid, flow velocity and surface geometry, A is the surface area exposed to the fluid, and ΔT is the temperature difference between the surface and the surrounding fluid. This calculator plugs your three inputs directly into that equation to give the heat transfer rate in watts.

HVAC and thermal engineers use it to size radiators, cooling coils and heat exchangers, electronics cooling engineers use it to check whether a heat sink and fan combination can dissipate a chip's power draw, and process engineers use it to estimate heat loss from tanks, pipes and reactor vessels to ambient air or process fluid.

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