A 10 kW experimental absorption heat transformer unit operating with self-circulation has been thoroughly tested. The self-circulation is obtained according to the thermosyphon principle. The pressure difference in the unit is achieved through a difference in hydrostatic pressures. Theoretical relationships for the pressure profiles within the different components of the heat transformer have been derived. Stabilising the self-circulation has been the primary objective in this work, rather than the optimisation of the efficiency of heating and cooling areas. A satisfactory stable operation with self-circulation has been achieved. A reference heat transformer plant, delivering 100 kW, has been designed and installed in a major pulp and paper mill. This unit is directly incorporated with one of the evaporation plants of the mill. Plant operation data obtained under real industrial conditions are presented.