Pipe Insulation Thickness Calculator

• Calculate modes. “Heat loss (given thickness)” evaluates the stack you enter; “Required thickness (target surface temp)” bisects the thickness of the outermost insulation layer until the surface reaches the target, keeping other layers (and any metal cladding) as entered.
• Pipe OD and wall. From the schedule picker (ASME B36.10M/B36.19M, EN and copper families) or typed. The wall's conductivity is set by the pipe material (steel 50, stainless 16, copper 385 W/m·K) and matters little next to the insulation.
• Layers. Any number of radial layers from the pipe wall outwards, each with its own conductivity and thickness — insulation, a second insulation for high temperatures, or a metal cladding. A cladding adds negligible resistance; its effect is through the surface emissivity.
• Thermal conductivity k. Presets are typical values near 50 °C; k rises with temperature, so for hot service use the manufacturer's value at the layer's mean temperature — the average of its two interface temperatures in the interface table. Choose Custom to enter it.
• Surface emissivity ε. Of the outermost surface only: ~0.9 for most jackets, canvas and painted surfaces; ~0.1 for bright aluminium; ~0.3 for dull stainless. Radiation is often half the outer heat transfer in still air.
• Wind speed. 0 = still air (natural convection, Churchill–Chu). With wind the forced-convection coefficient (Hilpert, cross-flow over a cylinder) is used where it exceeds the natural one; radiation is added on top.
• Inner film coefficient h_i. Fluid-to-wall convection inside the pipe. It is rarely limiting for insulated pipe — 500–10,000 W/m²·K for liquids, 20–200 for gases, 5,000–50,000 for condensing steam.
• Axial cooling. With a length and mass flow the fluid's excess temperature decays as exp(−L/(ṁ·cp·R_total)); the outlet temperature and the total loss follow. Without a mass flow the total is simply W/m × length at the inlet temperature.
• Outputs. Heat loss per metre and per m² of outer surface; the temperature at every interface; efficiency = reduction versus the bare pipe; and the resistance breakdown, where the largest term shows what is controlling the loss.

• Steady one-dimensional radial conduction through concentric layers in perfect contact (no contact resistance, no gaps, no wet insulation), with a single uniform ambient.
• Constant conductivity per layer. Real k rises with temperature — on hot service take the manufacturer's value at the layer's mean temperature (the average of its two interface temperatures), not the room-temperature figure.
• Outer surface: horizontal cylinder in air. Natural convection by Churchill–Chu, forced by Hilpert cross-flow (the larger of the two is used, not a combination), plus linearised radiation to surroundings taken at the ambient air temperature. No solar gain, no rain.
• Axial cooling assumes a single-phase fluid with constant cp and a constant ambient along the run; condensing steam holds its temperature and is not cooled this way.
• Personnel protection: the target surface temperature is a design choice. ISO 13732-1 thresholds depend on the surface material and contact time — roughly 60 °C for bare metal and 70 °C for jacketed insulation at 1 s contact — verify against the standard.
• Cold service: the same network gives the heat gain and the surface temperature, but condensation is not checked here — use the pipe condensation calculator for dew-point risk.
• Not modelled: buried or soil-covered pipe, tracing, flanges and supports (which typically add 10–25% to a well-insulated line), and transient warm-up or cool-down.

The SimuPipe solver carries heat loss along a pipe as an overall coefficient U; the total resistance here gives that U (U = 1/(R_total·π·D_o), D_o = outer surface diameter). The solver's accuracy is documented case by case on the validation page (53 published cases, including a diabatic gas pipe with convective heat loss).

None of these methods are ours — check them at the source.

• ISO 12241:2022. Thermal insulation for building equipment and industrial installations — Calculation rules — the industry calculation method for insulated pipe heat loss and surface temperature.
• ASTM C680. Standard Practice for Estimate of the Heat Gain or Loss and the Surface Temperatures of Insulated Flat, Cylindrical, and Spherical Systems — the equivalent ASTM practice; both use the same series-resistance model.
• ISO 13732-1:2006. Ergonomics of the thermal environment — Methods for the assessment of human responses to contact with surfaces — Part 1: Hot surfaces — safe-touch surface temperature thresholds.
• Churchill, S. W. and Chu, H. H. S. (1975). "Correlating equations for laminar and turbulent free convection from a horizontal cylinder." Int. J. Heat Mass Transfer, 18(9), 1049–1053. doi:10.1016/0017-9310(75)90222-7 — the natural-convection correlation used for still air.
• Hilpert, R. (1933). "Wärmeabgabe von geheizten Drähten und Rohren im Luftstrom." Forschung auf dem Gebiet des Ingenieurwesens, 4, 215–224 — the crossflow forced-convection correlation used with wind.
• Incropera, F. P., DeWitt, D. P., Bergman, T. L. and Lavine, A. S. Fundamentals of Heat and Mass Transfer, Wiley — the composite-cylinder resistance network, air properties, and the axial decay solution.