PURPOSE: To reduce the loss of heat by ventilation, by a method wherein an ventilation layer opened to an exterior and an indoor bottom part such as a part under a floor communicates with each other through a reversible type fan, and the outside air is sent from a ventilation layer on the side of sunshine to a ventilation layer on the side of non-sunshine in winter, and the outside air is sent in the reverse direction by the counterwise rotation of the fan is summer.

CONSTITUTION: Air is sent through each of reversible fans 6a, 6b and through a heating apparatus 7a or a cooling apparatus 7b. In winter, the air for ventilation is sucked from an outdoor part on the side of sunshine and is discharged to the outdoor part on the side of non-sunshine through the route of an air vent 2a, a ventilation layer 3a, a part 4 under a floor, an air vent 4a, a part 9 in a room, an air vent 5a, a part 5 in a ceiling, a ventilation layer 3b, and air vent 2b in that order. The air for heating is circulated in the cycle of the heating apparatus 7a, the part 4 under the floor, the air vent 4a, the part 9 in the room, the air vent 5a, the part 5 in the ceiling, a vertical duct 8, and the heating apparatus 7a in that order. In summer, each of the reversible fans 6a, 6b is driven counterwise, and the air for the ventilation flows in the reverse direction of the route in winter. The air for cooling is circulated by the shift of dampers 8a, 8b in the cycle of the cooling apparatus 7b, the part 5 in the ceiling, the air vent 5a, the part 9 in the room, the air vent 4a, the part 4 under the floor, the vertical duct 8 and the cooling apparatus 7b in that order.