Pipe Insulation Thickness Calculator
Calculate the minimum insulation thickness required for a pipe to limit heat loss to a desired value, based on cylindrical heat conduction principles.
Results will appear here.
Formulas Used
Heat loss per unit length through a cylindrical insulation layer with outer convection:
q = 2π·ΔT / [ ln(r₂/r₁)/k + 1/(h·r₂) ]
Where:
- q — heat loss per unit length (W/m)
- ΔT = Tpipe − Tamb — temperature difference (K)
- r₁ — pipe outer radius = insulation inner radius (m)
- r₂ — insulation outer radius (m) — solved numerically
- k — insulation thermal conductivity (W/m·K)
- h — external convective heat transfer coefficient (W/m²·K)
Critical radius of insulation (adding insulation below this radius increases heat loss):
rcr = k / h
The required r₂ is found by bisection, solving for q = qmax.
Assumptions & References
- Steady-state, one-dimensional radial heat conduction through a hollow cylinder (Fourier's Law).
- Insulation thermal conductivity k is assumed constant (temperature-independent). For wide temperature ranges, use a mean temperature value of k.
- Pipe wall thermal resistance is neglected (pipe wall conductivity is typically much higher than insulation).
- Outer surface heat transfer is modelled as pure convection. Radiation is not included; for hot surfaces in open air, the effective h should be increased to account for radiation (typically +5–10 W/m²·K).
- Uniform temperature along the pipe length is assumed.
- Annual energy estimate assumes 8,760 hours of continuous operation per year.
- References: Incropera & DeWitt, Fundamentals of Heat and Mass Transfer, 7th ed., §3.3 (Cylindrical Systems); ASHRAE Handbook — Fundamentals, Chapter 26 (Heat, Air, and Moisture Control in Building Assemblies); EN ISO 12241 — Thermal insulation for building equipment and industrial installations.