The paper presents analysis of the ways in which waste heat collected from the upper space of the plastic tunnel may be used. Warm air sucked from the upper space was pumped to a diffuser located in the process water tank. The assumed method was theoretically analysed and then tests were carried out in a real facility. Air bubbles moving in the liquid layer transferred heat, which they contained. The initial research, carried out according to the assumed method, did not bring satisfactory results. Nonetheless, some relations and possibilities of improvement of the described method by increasing the degree of complexity and the system costs were reported.