A compensator can be built-into a heating system to absorb pipe linear expansion as an alternative to an expansion loop.

Pipe linear expansion in a heating system is caused by the difference between the operating temperature and ambient temperature and by variations in media temperature. A compensator can be built-into the system to compensate for this linear expansion, as an alternative to an expansion loop. The compensator can be a hinged or axial type. Pipe fixtures and lateral pipe guides have to be built-in if a compensator is used to deal with the expansion. 

A hinged compensator allows a pipe corner to move, so that the pipe expansion can be absorbed by the compensator. An axial compensator works by allowing two pipes to move against each other, thus absorbing the expansion. A flexible bellow prevents the system from leaking.
District heating systems often use an alternative to compensators. Instead, pipes are stressed/distorted in such a way that any expansion is minimised. To deal with expansion, stressed steel pipes and even extra-strength steel pipes are used as an alternative or in a combined solution.