Paritian

Heat & Fluids

Pipe Insulation Heat Loss Calculator

Heat lost by a hot pipe with and without insulation, the saving, the energy wasted per day and the critical insulation radius, with the cross-section drawn to scale.

Results

Heat loss, insulated 76.6 W
Heat loss per metre 7.66 W/m
Heat loss, bare pipe 276.5 W
Saving from the insulation 72.3 %
Energy lost per day 1.84 kWh
Critical insulation radius 3.50 mm
The shape, to scale
Pipe Insulation Heat Loss CalculatorPipe Insulation Heat Loss Calculator: r₂ = 31.0 mm, r₁ = 11.0 mmr₂ = 31.0 mmr₁ = 11.0 mm
How it changes
Heat loss per metreInsulation thickness 0 – 60. Heat loss per metre: 27.646 → 4.59566; Bare pipe, per metre: 27.646 → 27.646Heat loss per metreBare pipe, per metre01020300102030405060Insulation thickness (mm)

The dashed line marks the value you entered.

What this tool does

Heat leaves an insulated pipe through two resistances in series: the insulation, which grows with the logarithm of the outer-to-inner radius, and the outer surface, which shrinks as the surface gets bigger. On thin pipes and wires this produces a surprise — up to the critical radius λ/h, a thin layer can actually lose more heat than the bare pipe, because it adds surface faster than resistance. For ordinary foam on heating pipes the critical radius is a few millimetres, so the second effect quickly wins; the chart shows the loss as the thickness grows. The pipe wall itself is ignored, which is fine for metal pipes.

Formula

q′ = ΔT ÷ [ln(r₂ ÷ r₁) ÷ (2πλ) + 1 ÷ (2π r₂ h)] · r_crit = λ ÷ h

Variables

SymbolMeaningUnit
dpPipe outside diametermm
tiInsulation thicknessmm
kInsulation thermal conductivity λW/(m·K)
tpTemperature of the pipe°C
taAmbient temperature°C
hOuter surface coefficient (still air ≈ 10)W/(m²·K)
lPipe lengthm
QTHeat loss, insulatedW
QLHeat loss per metreW/m
QBHeat loss, bare pipeW
SVSaving from the insulation%
EDEnergy lost per daykWh
RCCritical insulation radiusmm

Worked example

  • Pipe outside diameter22 mm
  • Insulation thickness20 mm
  • Insulation thermal conductivity λ0.035 W/(m·K)
  • Temperature of the pipe60 °C
  • Ambient temperature20 °C
  • Outer surface coefficient (still air ≈ 10)10 W/(m²·K)
  • Pipe length10 m
  • Heat loss, insulated76.6 W
  • Heat loss per metre7.66 W/m
  • Heat loss, bare pipe276.5 W
  • Saving from the insulation72.3 %
  • Energy lost per day1.84 kWh
  • Critical insulation radius3.50 mm

Limitations

  • The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
  • The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.