Pipe Insulation Heat Loss Calculator

The heat loss from an insulated pipe, the temperature on the outside of the insulation, and the saving over a bare pipe.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Heat flows from the hot pipe through the insulation, then from the outside surface to the air. The two resistances add. For a pipe the resistance of the insulation depends on the logarithm of the ratio of the outer to the inner radius, and the surface resistance on the outer area.

The heat loss per metre is the temperature difference divided by the total resistance. The surface temperature is the ambient temperature plus the heat loss times the surface resistance. The outer coefficient includes convection and radiation and is typically 8 to 12 W/m²·K in still indoor air.

Formulas used

  • R_i = \frac{\ln(r_2/r_1)}{2\pi k}
  • R_s = \frac{1}{h\,2\pi r_2}
  • q = \frac{T_p - T_a}{R_i + R_s}

Worked example

With the default numbers in the calculator above:

  1. Radii: 44.45 and 94.45 mm
  2. Thermal resistance of the insulation, per metre: 2.999 m K/W
  3. Thermal resistance of the outer surface film, per metre: 0.1685 m K/W
  4. Heat loss per metre: 51.78 W/m
  5. Total heat loss over the length: 2.589 kW
  6. Outside surface temperature of the insulation: 28.72 °C
  7. Bare pipe (same surface coefficient) and the saving: 88.7 % saving

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

How thick should insulation be?

Thicker insulation saves more energy but with diminishing returns. The economic thickness depends on the cost of heat and of the insulation. A surface above about 60 degrees Celsius can burn on contact.

What conductivity does mineral wool have?

About 0.035 to 0.045 W/m·K at normal temperatures. It rises with temperature.

Is the pipe wall included?

No. For a steel pipe its resistance is negligible compared with the insulation.

Related calculators

Further reading: Incropera and DeWitt, Fundamentals of Heat and Mass Transfer; Cengel, Heat and Mass Transfer.

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