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Insulation thickness & heat loss
Enter the hot or cold face, the ambient, and the surface temperature you want to hold. The calculator returns the thickness needed, the next stock size, and what the remaining loss amounts to over a year.
Your figures
Steam line, vessel wall or cold room — a negative value is fine.
60 °C is the usual personnel-protection limit on a hot surface.
Mineral wool 0.040–0.050, PUF 0.022, EPS 0.036, calcium silicate 0.060.
Total area to be insulated, for the loss and cost figures.
Result
Thickness
- Insulation thickness
- 39 mm
- Next stock thickness
- 40 mm
k × (130 K) ÷ (10 W/m²K × 15 K)
Insulation is bought in these steps, in one or two layers
Heat flow
- Heat flux
- 150 W/m²
- Total loss
- 15 kW
- Annual energy
- 120,000 kWh
- Bare surface loss
- 145 kW
Through the surface at 50 °C into 35 °C air
Over 100 m²
8,000 hours a year
What it would lose with no insulation at all — the saving
Questions
What surface temperature should I target?
Sixty degrees is the usual personnel-protection limit on a surface someone can touch. Where the aim is saving energy rather than protecting people, the economic thickness is normally greater than the one safety alone requires.
Does this work for cold rooms and chilled lines?
Yes — enter a hot face below ambient and it works the same way. But a cold face also needs a vapour barrier on the warm side. Without one, moisture condenses inside the insulation, ice forms, and the insulation stops working. The calculator warns you when the face is below ambient.
Where does the surface coefficient come from?
Combined convection and radiation from a clad surface to still air is taken at 10 W per square metre per kelvin, which is the figure the trade sizes with. It is not truly constant — it rises with temperature difference and sharply with wind — so an exposed outdoor line needs more than this suggests.
What about pipe curvature?
This calculates on a flat basis, which is accurate for large vessels and slightly conservative for small-bore pipe, where curvature increases the outer surface area and thus the loss. For small pipe at high temperature, use the supplier's cylindrical tables.