Insulation Thickness Calculator
Calculate the required insulation thickness for a flat wall or cylindrical pipe to meet a target heat flux or surface temperature limit.
Results will appear here.
Formulas Used
Flat Wall — Thickness:
Total resistance: Rtotal = ΔT / q
Insulation resistance: Rins = Rtotal − 1/h
Thickness: d = k · Rins
Flat Wall — Heat Flux:
q = ΔT / (d/k + 1/h)
Cylindrical Pipe — Heat Loss per Unit Length:
Q/L = 2π·ΔT / [ln(r₂/r₁)/k + 1/(h·r₂)]
For thickness mode, r₂ is solved numerically (bisection) since the equation is implicit in r₂.
Critical Radius (cylinder):
rcrit = k / h — adding insulation below this radius increases heat loss.
Assumptions & References
- Steady-state, one-dimensional heat conduction (no heat generation).
- Thermal conductivity k is constant (temperature-independent).
- Flat wall: uniform cross-section; cylindrical pipe: concentric layers.
- Outer surface convection resistance = 1/h (flat) or 1/(h·r₂) per unit length (cylinder).
- Inner surface resistance is neglected (pipe wall assumed isothermal at T₁).
- Radiation heat transfer is not included.
- Reference: Incropera & DeWitt, Fundamentals of Heat and Mass Transfer, 7th Ed., Chapters 3 & 3.7.
- Typical k values: mineral wool 0.03–0.05 W/m·K, foam glass 0.04–0.06 W/m·K, polyurethane foam 0.022–0.028 W/m·K.