Estimates steady-state heat loss per metre: Q′ = ΔT / (Rcond + Rsurf).
Tender-stage only. Verify to project spec and manufacturer data.
Steady-state model only. Does not account for radiation, moisture, condensation, or pipe-wall conduction (negligible for metal pipes, may matter for plastics).
For design guidance only. Always verify with a qualified engineer.
About this pipe heat loss calculator
This free pipe heat loss calculator estimates the steady-state heat loss per metre from an insulated (or bare) pipe carrying a hot fluid. Enter the pipe outside diameter, insulation thickness and conductivity, the fluid and ambient temperatures, and a surface film coefficient, and it returns the heat loss in W/m, the insulation surface temperature, and, using the optional run length, operating hours and energy cost, the total wattage, annual energy and annual cost. It is built for UK building-services engineers, mechanical contractors and estimators who need a quick tender-stage check on pipework insulation.
How the heat loss is calculated
The tool models one-dimensional radial conduction through the insulation in series with the outer surface film, per BS 5422:2023 and CIBSE Guide C §3. The conduction resistance is Rcond = ln(r₂/r₁) / (2πk) and the surface resistance is Rsurf = 1 / (h·2πr₂), giving heat loss Q′ = ΔT / (Rcond + Rsurf). It also compares the result against a bare pipe and flags whether the loss sits within the BS 5422 maximum-permissible limit for the diameter and temperature difference. Radiation, moisture, condensation and pipe-wall conduction are not modelled, so it is for design guidance only. Always verify against project specification, manufacturer data and a qualified engineer.
Frequently asked questions
Which insulation materials can I model?
Preset conductivities (k) are provided for aerogel (0.018), phenolic and PIR/PUR (0.025), mineral wool (0.040) and cellular glass (0.045) W/m·K, or you can enter a custom k value to match your chosen insulant.
What surface film coefficient should I use?
Pick from the presets: 6 for still indoor air, 10 for light air movement, 15 for a drafty plantroom or 25 for outdoor/windy conditions (W/m²·K). Or enter a custom h. The film resistance is combined in series with the insulation conduction resistance.
Can it handle a bare pipe?
Yes. Set the insulation thickness to 0 and the calculator drops the conduction term, returning the heat loss from the bare pipe surface alone. Which is also used as the baseline for the insulated-versus-bare saving comparison.