Convection Heat Transfer Calculator (Q = h·A·ΔT)

How it works

Q = h × A × (T_s − T_∞) · heat flux q = Q ÷ A = h × ΔT · thermal resistance R = 1 ÷ (h × A) · 1 W/m²·K = 0.1761 Btu/h·ft²·°F

Convection carries heat between a surface and a moving fluid. Newton’s law of cooling lumps the complicated flow near the wall into one heat-transfer coefficient h, so the heat rate is simply h times the area times the temperature difference. The value of h is what matters: still air gives only 2–25 W/m²·K, a fan raises it ten-fold, water is a hundred times better than air, and boiling or condensation is higher still (ranges from Incropera’s Fundamentals of Heat and Mass Transfer, Table 1.1). For a precise h use a Nusselt-number correlation for your geometry and flow.

Worked example

A 2 m² surface at 80 °C in still air at 20 °C, with free-convection h = 10 W/m²·K, loses 10 × 2 × 60 = 1,200 W, a heat flux of 600 W/m². Its convective resistance is 1 ÷ (10 × 2) = 0.05 K/W, and over a day it gives off 28.80 kWh. With a fan (h = 50) the same surface would lose 6,000 W.

Sources: Incropera et al. — Fundamentals of Heat and Mass Transfer, Table 1.1 (typical h values) · Engineering ToolBox — Convective heat transfer

Frequently asked questions