Heat Transfer Coefficient Chart

Convection coefficients for twenty common situations in air, water, oil and steam — natural convection, forced convection, boiling and condensation, in both unit systems.

Data verified 2026-09-29 · based on compilations as published 2024–2026

Quick Answer

Convection Heat Transfer Coefficients

Ranges are order-of-magnitude engineering guidance, not a substitute for a correlation. A convection coefficient is not a material property — it is a function of the flow field, and the same fluid can span the whole range depending on whether the flow is laminar or turbulent, the characteristic length, and the geometry. Forced convection up to about 500 W/m²·K in air and 15 000 in water is where most air and water heat exchangers operate. Boiling and condensation are not convection in the usual sense — they transfer latent heat and reach coefficients one to two orders of magnitude above single-phase flow, which is why heat pipes and steam systems move so much heat in a small area.

Why the Coefficient Is Not a Material Property

Unlike thermal conductivity, which belongs to the material and can be looked up once, a convection coefficient belongs to the flow situation. The same water in the same pipe can have an h of 200 or 15 000 depending only on whether the flow is laminar or turbulent.

The physical reason is that convection is conduction across a thin stagnant film at the surface, and the only thing that varies is how thin that film is. In laminar flow the film is thick and h is low; turbulence scours the film down to almost nothing and h rises by an order of magnitude. This is why a pump or fan buys far more heat transfer than a bigger surface does: doubling the velocity may double or triple h, while doubling the surface only doubles the area.

The coefficient is usually obtained from a correlation of the form Nu = C·Re^m·Pr^n, where the Nusselt number contains h, the Reynolds number contains velocity and geometry, and the Prandtl number contains the fluid's properties. That is why the entry you need is not "water" but "water in turbulent tube flow" — the geometry matters as much as the fluid.

Which Resistance Dominates

The reason to look up a convection coefficient is almost always to find out which thermal resistance in a chain is the limiting one, because that is the only one worth improving.

R = 1/h for a convective surface, and t/k for a conduction path. Take a forced-air heat sink: h = 50 W/m²·K on the air side gives R = 0.02 m²·K/W. A 5 mm aluminium fin base at k = 200 gives R = 0.000025 — three orders of magnitude smaller. Essentially all the resistance is on the air side, which is why heat sink design is entirely about getting air across more surface, and why adding metal does nothing.

Now take the same sink with water at h = 5000: R = 0.0002, which is still the dominant resistance but now only eight times the conduction term. This is the crossover that makes liquid cooling so much more effective — a twentyfold drop in the air-side resistance means either a hundredfold smaller sink for the same performance, or a much cooler device.

The same reasoning drives the design of boilers and condensers. Because boiling and condensing coefficients reach 100 000, the phase-change side contributes almost no resistance — which is why the tube wall and the other fluid set the size of the equipment, and why boiling surfaces are designed for bubble nucleation rather than for extra area.

Frequently Asked Questions

What is a typical heat transfer coefficient for air?

Between 3 and 25 W/m²·K in natural convection, and 10 to 500 in forced convection depending on velocity and geometry. The wide range is the point: a still-air surface and a high-velocity duct flow differ by a factor of 50 or more. For a rough design estimate, use 10 for natural convection, 25 for a slow fan and 100 for a fast one.

How much better is water cooling than air cooling?

Roughly 20 to 100 times, in terms of the convection coefficient. Water in turbulent tube flow reaches 1 500 to 15 000 W/m²·K against 10 to 500 for forced air. Part of that is water's far higher thermal conductivity and volumetric heat capacity, but the larger part is that water's higher density and viscosity allow much higher Reynolds numbers in the same geometry.

Why are boiling coefficients so high?

Because boiling transfers latent heat rather than sensible heat, and the bubbles themselves stir the liquid violently right at the surface. Pool boiling of water reaches 3 000 to 100 000 W/m²·K against about 1 000 for the same water in forced single-phase flow. That is why heat pipes and steam systems transfer large amounts of heat across small areas, and why a boiler is limited by its tube wall and its other fluid rather than by the boiling surface.

Can I use these values directly in a calculation?

Only for an order-of-magnitude estimate. A convection coefficient depends on flow regime, velocity, characteristic length, surface orientation and fluid properties, and the ranges here span a factor of fifty within a single row. For design work, compute h from a correlation for your specific geometry, or take it from a measured value on similar equipment rather than from a general chart.

What is the difference between natural and forced convection?

Natural convection is driven by buoyancy — heated fluid rises because its density falls. Forced convection is driven by an external fan or pump. Because forced convection produces much higher velocities, it gives coefficients roughly an order of magnitude higher: 3 to 25 W/m²·K in air naturally against 10 to 500 when forced. Natural convection is used where noise, reliability or cost rules out a fan.

Related

• Thermal Conductivity Chart
• Specific Heat Capacity Chart
• Density Chart
• Viscosity Chart
• Boiling Point Chart
• Pressure Conversion Chart

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

Data Sources

Cross-checked against:

• Ranges cross-checked between two independent heat-transfer references rather than taken from one table
• The boiling and condensation ranges checked against published phase-change correlations
• Imperial values recomputed from SI at build time against the exact 0.176110 conversion factor

Derived values — the following values on this page are calculated, not taken directly from the standard:

Ranges are engineering guidance for order-of-magnitude work. A convection coefficient is a property of the flow situation, not of the fluid, and the same fluid spans the entire range depending on velocity, geometry and whether the flow is laminar or turbulent. For design work, use a correlation for the specific geometry or a measured value from similar equipment.

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