KEVOS® MAKEOS · Materials
Heat Loss from an Insulated Pipe
How much heat does this insulated pipe lose, and how hot is the outside surface?
Heat loss per metre and in total from an insulated pipe by radial conduction and surface convection, the outer surface temperature and the yearly energy cost.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Pipe outside diameter | mm | Outside diameter of the pipe (e.g. 60.3 mm for DN50). |
| Insulation thickness (0 = bare) | mm | Insulation thickness; 0 for bare pipe. |
| Insulation conductivity | W/(m·K) | Conductivity of the insulation at its mean temperature (mineral wool about 0.04 W/m·K). |
| Pipe temperature | °C | Temperature of the pipe wall (fluid temperature). |
| Ambient temperature | °C | Surrounding air temperature. |
| Outside surface coefficient | W/(m²·K) | Combined convection and radiation coefficient at the outer surface (about 8–12 still air indoors; higher outdoors and for bare metal). |
| Pipe length | m | Length of pipe. |
| Operating hours per year | h | Hours per year the line is hot. |
| Heat energy price | AUD/kWh | Cost of heat delivered (fuel price ÷ boiler efficiency). |
Method and formulas
- Resistance per metre R = ln(r₂ ÷ r₁) ÷ (2π k) + 1 ÷ (2π r₂ h).
- Heat loss per metre q = (Ti − Ta) ÷ R; total = q × L.
- Surface temperature = Ta + q ÷ (2π r₂ h); cost = loss × hours × price.
- Example: 50 mm insulation on a 60.3 mm pipe at 150 °C loses 31.794 W/m; the surface runs at 26.313 °C.
Limitations
- Steady state; the pipe wall resistance is neglected and the surface coefficient is user-estimated.
- Valves, flanges and supports lose much more per metre if left bare.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose insulation thickness for steam, hot water or oil lines
- Estimate savings from insulating bare pipe
- Check surface temperature for burn protection
Who it is for
- Process engineers
- Energy managers
- Maintenance engineers
What you get
- Heat loss per metre and total
- Outer surface temperature
- Energy and cost per year
Interpreting the result
- Compare the cost per year with insulation cost to find the payback; check surface temperature for safety.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–378. Topic reference; no source tables or recommended settings are reproduced.
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