Liceo is the oldest and most prestigious theater in Barcelona, especially well known as an opera house. Since 1847 it has been the scene of all kinds of opera, and a meeting place for the Catalan bourgeoisie. The ventilation of the building is taken care of by a Systemair DV240 air handling unit with an adiabatic humidifier and a sorption rotary heat exchanger. This project was special because of the extremely small door dimensions the unit had to pass through; 0.9x2 meters. To make this possible, the 8 meter long, 3.5 meter wide and 4.5 meter tall air handling unit was divided into smaller parts and then assembled inside the building.