Overall Heat Transfer Coefficients
Typical overall heat transfer coefficients for heat exchangers, walls, and insulated systems.
Overview
Overall heat transfer coefficients (U) represent the total thermal conductance from one fluid to another across a heat exchanger wall. These coefficients combine the effects of conduction through the wall and convection on both sides. The values are highly dependent on fluid types, velocities, flow regimes, and surface conditions. The coefficients below provide typical engineering estimates for initial design calculations.
Data Table
The following 9-row table is a selected summary for quick lookup. The complete 15-row original source table is preserved in the restored source table below.
Application | U (Overall Coefficient)(W/(m²·K)) |
|---|---|
| Water to Water | 800 |
| Water to Oil | 350 |
| Water to Glycol Solution | 500 |
| Steam to Water | 1500 |
| Steam to Oil | 300 |
| Air to Air (Finned Tube) | 30 |
| Air to Water (Finned Tube) | 40 |
| Gas to Gas | 25 |
| Condensing Vapor to Liquid | 1000 |
Source: engineeringtoolbox.com
Restored Original Source Tables
The following tables are restored from the original source page to preserve the complete reference data.
The first detected source table with navigation/search rows is a page layout artifact and is not heat-transfer coefficient data. The engineering table from the source is preserved below.
The original source emphasizes that the overall heat-transfer coefficient is approximate and can vary widely with fluid velocity, surface condition, fouling and exchanger geometry.
Example - Water to Air Heat Exchanger
The source example uses a copper heat-transfer surface between water and air or gas. From the restored table, the overall heat-transfer coefficient is U = 13.1 W/(m2 K). For water at 80 degC and air at 20 degC, the heat flux is:
Heat Transfer Coefficients in Heat Exchangers
Fluid | Material in transmission surface | Fluid | U(Btu/(ft2 hr oF)) | U(W/(m2 K)) |
|---|---|---|---|---|
| Water | Cast Iron | Air or Gas | 1.4 | 7.9 |
| Water | Mild Steel | Air or Gas | 2 | 11.3 |
| Water | Copper | Air or Gas | 2.3 | 13.1 |
| Water | Cast Iron | Water | 40 - 50 | 230 - 280 |
| Water | Mild Steel | Water | 60 - 70 | 340 - 400 |
| Water | Copper | Water | 60 - 80 | 340 - 455 |
| Air | Cast Iron | Air | 1 | 5.7 |
| Air | Mild Steel | Air | 1.4 | 7.9 |
| Steam | Cast Iron | Air | 2 | 11.3 |
| Steam | Mild Steel | Air | 2.5 | 14.2 |
| Steam | Copper | Air | 3 | 17 |
| Steam | Cast Iron | Water | 160 | 910 |
| Steam | Mild Steel | Water | 185 | 1050 |
| Steam | Copper | Water | 205 | 1160 |
| Steam | Stainless Steel | Water | 120 | 680 |
Source: engineeringtoolbox.com
Heat Transfer Rate Calculator
Heat Transfer from Overall U Value
Unit Converter
Overall Heat Transfer Coefficient Unit Converter
The exact source conversion is: 1 Btu/ft2 hr degF = 5.678 W/m2 K = 4.882 kcal/h m2 degC.
Engineering Notes
- Approximate Values: The listed
Uvalues are standard estimates for clean surfaces and normal operating conditions. Fouling, scaling, or unusual fluid properties can significantly reduce actual performance. - Finned Surfaces: Air-side coefficients are low, so finned tubes are used to increase surface area and improve the overall
Uvalue for gas-to-liquid exchanges. - High
Ufor Condensation: Steam condensation and liquid-liquid exchanges (e.g., water-water) typically have very high coefficients due to the high heat transfer coefficients associated with phase change and high fluid velocities. - Design Margin: For critical applications, a detailed analysis considering specific fluid properties, velocities, and geometries is required. These typical values are suitable for preliminary sizing or feasibility studies.
- Impact of Material: The wall material's thermal conductivity also contributes, but its effect is often minor compared to the convective resistances on either side.