Convective Heat Transfer Calculator

Calculate a first-pass convection heat-transfer rate, heat flux and stated-period energy from an explicit h-value, area and temperature difference.

Enter an appropriate convection coefficient for the real fluid, flow regime, geometry and temperature range. This tool does not select h for you.

Convective heat-transfer rate750 W2,559.107 Btu/h
Heat flux750 W/m²q″ = h × ΔT
Energy over stated duration0.75 kWh2,559.107 Btu

Important: the temperature difference must be representative of the local surface-to-fluid driving force. The energy result assumes that h, area and temperature difference remain constant for the stated duration. For a heat exchanger with varying temperatures, use an LMTD or effectiveness-NTU method instead.

Method and variables

Heat-transfer rate: Q̇ = h × A × ΔT. Heat flux: q″ = h × ΔT.

  • h — convection coefficient for the actual fluid, geometry and flow condition
  • A — heat-transfer surface area
  • ΔT — representative local surface-to-fluid temperature difference

Worked example

Air with h = 25 W/(m²·K) across a 1 m² surface that is 30 K warmer than the air transfers 25 × 1 × 30 = 750 W. If that condition remains constant for 8 hours, the associated energy is 6 kWh.

Using the duration result

The duration field converts the calculated rate to energy only. It is useful for a transparent constant-condition scenario, but it is not a weather, thermostat, duty-cycle or energy-cost model.

Important limits

The calculator does not estimate h, include radiation or conduction, or model boundary-layer development. For a heat exchanger with changing stream temperatures, use a suitable LMTD or effectiveness-NTU design method. Treat the stated duration result cautiously whenever temperature, flow or surface conditions vary.

Related tools

Nusselt Number Calculator · LMTD Heat Exchanger Calculator · Heat Transfer Calculators

Frequently asked questions

What equation does this convective heat-transfer calculator use?
It uses Q̇ = h × A × ΔT: convection coefficient times exposed area times the representative surface-to-fluid temperature difference.

How do I choose the convection coefficient h?
Use a value that represents the actual fluid, geometry, flow regime and temperature range. This calculator applies your stated coefficient; it does not select or validate a correlation for h.

What does the energy result represent?
It multiplies the calculated heat-transfer rate by the operating duration you enter. It assumes the coefficient, area and temperature difference stay constant for that period.