Convective Heat Transfer Rate Calculator

How it is calculated

The tool applies Newton's law of cooling: Q = h × A × ΔT. Here h is the convection coefficient in W/(m²·K), A is the wetted surface area in m², and ΔT is the surface-to-fluid temperature difference in K (a difference of 1 K equals 1 °C). The result Q is in watts and is also shown in kW (Q ÷ 1000), together with the heat flux q = h × ΔT in W/m². Area must be greater than zero; h and ΔT are not restricted, so a negative ΔT gives a negative Q, meaning heat flows into the surface instead of out of it. The tool does not estimate h for you.

Common mistakes

• Entering area in cm² or mm² instead of m². The coefficient is per square metre, so a 1.5 m² panel typed as 15000 cm² gives a result 10,000 times too large.
• Using the surface temperature or the fluid temperature alone instead of their difference. ΔT must be surface minus fluid.
• Guessing h. It depends on the fluid, velocity and geometry, and values for still air and for flowing water differ by orders of magnitude, so the answer is only as good as h.
• Using the wrong sign: if the fluid is hotter than the surface, ΔT is negative and the negative Q is correct, not an error.
• Applying the result to a surface that also radiates strongly; this formula covers convection only and ignores radiation and conduction.