Abstract <p>The paper presents mathematical simulation of reversible filtration of air flow through a thin-walled plastic tubular heat exchanger with an internal diameter of 3.2 mm, taking into account the phase transition at positive outdoor temperatures. The temperature profiles of the air and the checkerwork material have been obtained in various cross-sections. Analysis of the results has shown that the displacement of the phase transition zone along the length of the checkerwork significantly affects the temperature characteristics of the air flow. As the indoor temperature increases (from 10 to 17°C), the zone of influence of the phase transition shifts to the colder end of the setup, changing the air temperature profile. The study has shown that the phase transition affects the air temperature, while its position along the length of the checkerwork determines this effect.</p>