Duco. D-system. DucoBox Energy Comfort D400 is a balanced ventilation unit with heat recovery. Within the DucoBox Energy Comfort range, the left/right exchange is done 100% via software thanks to a patented double bypass principle. The demand control of the DucoBox Energy Comfort D400 results in intelligent and energy-efficient operation. Together with the smart demand control based on CO2 and humidity, the dynamic air distribution filters provide exceptional efficiency within this compact unit. The compact and quick-to-install 2-zone valves provide the most energy-efficient result achievable with system D. Bear in mind that the zone control reduces noise by at least 30%! Comfort at its best!