To provide a heat insulation resin duct used in a heat exchange type central ventilation system of a dwelling house with high air-tightness and high heat insulation, embodied light, having heat insulating performance, involving less pressure loss, and capable of preventing fungi from stagnating in the duct, and to provide a ventilation system which can preclude propagation of sounds between rooms via the duct.

The heat insulation resin duct for sucking the air or exhausting is structured so that a soft thickness part made of foaming resin with independent bubbles is provided by fusion attachment or adhesion to the upper part of a spiral reinforcement made of resin and the inner surfaces of the duct consisting of the spiral reinforcement and the soft thickness part are smoothed, and the invention further includes a suction/exhaust system branching chamber having a suction piping and an exhaust piping leading to the inside of the room and a heat exchange type ventilating device. Part or the whole of the piping of the branching chamber where a sound absorbing material is provided inside the chamber and the piping tying the branching chamber to the heat exchange type ventilating device is formed from the heat insulation resin duct, and thereby the intended total heat exchange type ventilation system is completed.