Outer surface (touch) temperature of an insulated or bare pipe and a personnel-protection touch-safety verdict, EN ISO 12241 radial resistance network (conduction annulus + surface film) per metre run.
Indicative only. Verify final design to BS 5422 / CIBSE and the relevant burn-safety standard.
For design guidance only. Always verify with a qualified engineer.
About this surface temperature calculator
This free surface and touch temperature calculator estimates the outer surface (touch) temperature of an insulated or bare pipe and gives a personnel-protection touch-safety verdict. Give it the service and ambient temperatures, the pipe outside diameter, the insulation thickness and conductivity, and the outer surface-film coefficient, and it returns the touch temperature, the heat loss per metre run and how much margin you have to the touch-safe limit. It is aimed at UK building-services engineers and insulation designers checking that hot pipework is safe to touch and meets BS 5422 personnel-protection intent at tender or commissioning stage.
How the surface temperature is calculated
The calculator uses the EN ISO 12241 steady-state radial resistance network for a cylinder. Conduction through the insulation annulus is Rcond = ln(r₂/r₁) / (2πλ) and the outer surface film is Rsurf = 1 / (h·2π·r₂), both per metre run. The heat flux is Q′ = ΔT / Rtot, and the surface temperature is back-calculated as Ts = Tambient + Q′·Rsurf. The result is then banded: safe at or below the touch-safe limit (default 60 °C per ASTM C1055 personnel protection), caution up to 70 °C (the BS EN ISO 13732-1 one-second bare-metal burn threshold), and burn risk above. A bare pipe has no conduction resistance, so its surface temperature equals the service temperature.
Frequently asked questions
What surface temperature is safe to touch?
The default limit is 60 °C, the ASTM C1055 simulated-skin temperature for a five-second contact before an irreversible burn. The 70 °C upper band is the ISO 13732-1 one-second burn threshold for smooth uncoated metal. Non-metallic cladding can tolerate a higher touch limit, which you can set.
Why does a lower film coefficient give a higher surface temperature?
A lower outer film coefficient h means the surface sheds heat to the air less readily, so it sits hotter for the same heat flux. Still indoor air (h ≈ 6) is the most conservative, safest-to-flag case; a windy outdoor surface (h ≈ 25) runs cooler.
How accurate is the result?
It is an indicative steady-state estimate that assumes a clean radial heat path and a uniform combined convective-plus-radiative surface film. Use representative design conductivity and film values, and verify the final design against BS 5422, CIBSE guidance and the relevant burn-safety standard.