Underlying hot water pipes can under appropriate conditions be seen with a thermal imager. It is the heat transfer that is visualised not the actual pipe.

Thermal imaging is an ideal method for 'mapping' pipe runs or locating them before digging or drilling. Leaking pipes will easily be recognised by irregular heat shapes.

Below is a close view of underlying pipes. In this survey holes were to be drilled into the concrete avoiding the pipes. A laser in parallax with the centre of the thermal image allowed exact positioning.

The image below is of a footpath with underlying heating pipes.

The images below show under floor heating systems in a domestic properties.

The aerial image below was taken from 3,000 feet. The white lines are underground heating pipes feeding a housing estate. A leak would show as a plume.