Convection Heat Transfer Calculator (Q = h·A·ΔT)
By Santaji GadepatilinUpdated November 5, 2026
Convection is heat carried away by a moving fluid, and its rate is set by the heat transfer coefficient h, the surface area and the surface-to-fluid temperature difference. This convection heat transfer calculator solves Q = h·A·(Ts − T∞) for any one unknown and lists typical h values — it pairs with calculating heat loss in piping.
How to use the convection heat transfer calculator
Enter the heat transfer coefficient h, the surface area and the surface and fluid temperatures. The calculator returns the heat transfer rate and the heat flux. Clear any input and enter Q to solve for it — for example the h needed to remove a known heat load.
Convection formula
Q = h × A × (Ts − T∞) · q = Q ÷ A
Worked example
A 2 m² surface at 80 °C in air at 25 °C with h = 25 W/m²·K:
- Q = 25 × 2 × (80 − 25) = 2,750 W
- Heat flux = 2,750 ÷ 2 = 1,375 W/m²
Typical heat transfer coefficients (2 m², ΔT = 55 K)
| Situation | h (W/m²·K) | Heat transfer rate |
|---|---|---|
| Free convection — air | 2 – 25 | 220 – 2,750 W |
| Free convection — water | 50 – 1,000 | 5,500 – 110,000 W |
| Forced convection — air | 25 – 250 | 2,750 – 27,500 W |
| Forced convection — water | 100 – 20,000 | 11,000 – 2,200,000 W |
| Forced convection — oil | 50 – 1,500 | 5,500 – 165,000 W |
| Boiling water | 2,500 – 100,000 | 275,000 – 11,000,000 W |
| Condensing steam | 5,000 – 100,000 | 550,000 – 11,000,000 W |
Notes
- Hot surfaces also lose heat by radiation — at 80 °C in still air it can equal the convective loss; see the Stefan–Boltzmann calculator.
- For heat transfer between two fluids through a wall, use an overall coefficient U and the LMTD calculator.
Frequently asked questions
What is the convection heat transfer formula?
Q = h × A × (Ts − T∞), where h is the convective heat transfer coefficient (W/m²·K), A the surface area and Ts − T∞ the difference between surface and fluid temperature.
What is a typical heat transfer coefficient for air?
About 2–25 W/m²·K in still air (natural convection) and 25–250 W/m²·K with forced air flow.
Is this the same as Newton's law of cooling?
Yes — Q = hAΔT is Newton's law of cooling. The physics version of that law gives the temperature-versus-time curve of a cooling object.
What does a negative result mean?
The fluid is hotter than the surface, so heat flows into the surface instead of out of it.