BIZOMAT 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). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Pipe outside diameter
- What it is
- The outside diameter of the bare pipe that the insulation is fitted onto.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the actual outside diameter for the pipe size, not the nominal size (DN).
What this means: Insulation thickness (0 = bare)
- What it is
- The thickness of the insulation layer around the pipe; zero treats the pipe as bare.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Thicker insulation lowers the heat loss and the outer surface temperature.
- Get it right
- Zero means a bare pipe, which uses only the outside surface coefficient.
What this means: Insulation conductivity
- What it is
- The thermal conductivity of the insulation material at its mean temperature, from the insulation maker’s data.
- Units and format
- Enter a number in W/(m·K): W/(m·K). The form accepts 0.005 W/(m·K) to 5 W/(m·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.04 W/(m·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the value at the mean insulation temperature; conductivity increases with temperature.
What this means: Pipe temperature
- What it is
- The temperature of the pipe wall, taken as the temperature of the fluid inside.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -200 °C to 1000 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Heat loss rises in direct proportion to the difference between pipe and ambient temperature.
- Get it right
- Enter degrees Celsius.
What this means: Ambient temperature
- What it is
- The temperature of the air surrounding the pipe.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -60 °C to 100 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the air temperature around the pipe, which can be higher in plant rooms than outdoors.
What this means: Outside surface coefficient
- What it is
- The combined convection and radiation coefficient at the outer surface, describing how readily heat leaves the outside of the insulation or bare pipe.
- Units and format
- Enter a number in W/(m²·K): watts per square metre per kelvin. The form accepts 1 W/(m²·K) to 1000 W/(m²·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 W/(m²·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from a heat transfer reference for the surface finish and air movement; wind raises it outdoors.
What this means: Pipe length
- What it is
- The total length of pipe of this size and insulation that is losing heat.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 1000000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total heat loss and yearly cost rise in direct proportion to length.
What this means: Operating hours per year
- What it is
- The number of hours each year that the pipe is hot.
- Units and format
- Enter a number in h: hours. The form accepts 0 h to 8784 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6000 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Yearly energy and cost rise in direct proportion.
- Get it right
- Count only the hours the line is actually at temperature.
What this means: Heat energy price
- What it is
- The cost of one kilowatt-hour of heat delivered to the pipe, which is the fuel price divided by the boiler or heater efficiency.
- Units and format
- Enter a number in AUD/kWh: Australian dollars per kilowatt-hour. The form accepts 0 AUD/kWh to 100 AUD/kWh. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.08 AUD/kWh as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Yearly cost rises in direct proportion.
- Get it right
- Use the cost of delivered heat, not the raw fuel or electricity price.
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.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Cold pipes, sweating and insulation
In Condensation Control by the Numbers
What it covers: How much water a cold pipe gathers in humid air, the insulation thickness that keeps its surface above the dew point, why a vapour barrier matters, and the valves left bare for access.
Method explained here · BIZOMAT original book
Transfer: hoses, lines and phase separators
In Cryogenic Liquids by the Numbers
What it covers: The nitrogen spent cooling a hose, its heat gain insulated and bare, the share that arrives as gas, phase separators and hose safety, and a slow top-up that delivered mostly vapour.
Method explained here · BIZOMAT original book
Heat Transfer by the Numbers
What it covers: Calculate heat flows in plant: energy and power, conduction through walls and pipe insulation, convection, radiation, economic insulation, heat exchangers and heating and cooling times.
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