Annular gap

The clearance between inner and outer pipe in double-walled systems or between pipe and shaft or brick chimney is referred to as an annular gap. This can be insulated, filled with insulation material and can be operated dependent on room-air.

A hollow annular gap is often used for air supply. The toxic exhaust gases are thus discharged via the inner tube and the fresh air is supplied through this gap (room-air independent operation mode).