Pipe insulation steady heat loss calculator

What this model answers

A cylindrical insulation layer has increasing area as heat moves outward. Its conduction resistance therefore depends on the logarithm of outer radius divided by inner radius, rather than a flat-wall thickness divided by a fixed area.

The external film adds a second resistance in series. This model fixes the pipe outside-surface temperature and calculates the temperature drop through insulation and the outer film. It does not start from a fluid bulk temperature and solve the pipe wall.

The Heat energy calculator estimates sensible energy for a temperature change. This pipe model instead estimates steady heat transfer per second under fixed boundary temperatures; energy and steady power are different quantities. The Layered wall thermal resistance calculator instead uses planar layers in series; a pipe’s logarithmic radial resistance must not be substituted into that planar formula.

Measure the right inputs

Enter pipe outside diameter and radial insulation thickness in millimetres. Conductivity is an entered material property; the outside film coefficient describes heat transfer at the insulation surface.

Pipe temperature is the boundary at the inner insulation radius. Ambient is the far-field surrounding temperature. Conductivity and film coefficient remain constant over the calculation even if the real properties vary with temperature.

Read the result in context

Positive heat loss means outward transfer from a warmer pipe. A colder pipe gives a negative signed result, representing inward heat gain. The calculated outer-surface temperature should lie between the two entered boundary temperatures in this resistance model.

The bare comparison uses the same film coefficient at the original pipe radius. Increasing outer area can initially outweigh added resistance below a critical radius, so an insulation increase does not mathematically guarantee reduced loss for every input set.

Work through the numbers

A 50 mm pipe with 25 mm insulation has inner and outer insulation radii of 0.025 and 0.05 metres. At conductivity 0.04 W/m K, the conduction resistance per metre is ln(2)/(0.08 pi).

With a ten W/m² K outer film and an eighty-to-twenty-degree boundary difference, heat loss is about 19.50 W/m. Ten metres loses about 195.04 W, and the outer surface is about 26.21 degrees in this ideal model.

Where the model stops

Steady radial conduction and entered external film only; no radiation, internal film, pipe wall, contact bridges, moisture or temperature-dependent properties.

The result does not establish condensation protection, touch safety, a vapor-barrier specification or an approved insulation design. Check actual material and installation requirements separately.