This paper presents the results of tests on the two-zone airflow pattern that forms in a room with displacement ventilation under conditions of various heat sources and airflow rates. The position of the interface layer between the zones was determined experimentally by tracer gas concentration measurement and by applying a plume model for a point heat source. The following heat sources were used: a plume simulator, a desk lamp, a computer, a round plate and a human body. Quasi-laminar diffusers supplied the air. The test results show that, in order to define the interface position in displacement ventilation where real extensive heat sources are used, it is possible to apply the experimentally completed model of a plume above a point heat source.