PURPOSE: To prevent dew from being condensed and a crack in an exhaust vent, by providing a space between a lengthwise exhaust vent and a hollow tube.

CONSTITUTION: A space 4A is provided between a lengthwise exhaust vent 4 and a hollow tube 2A. With such an arrangement, humidity does not come to the exhaust vent 4 from a collective stack body 2, so that dew does not condense in the vent 4. Besides, fire hazard can be prevented, even if a part of vent is broken, as well as to prevent a crack and to eliminate the deficits of a concrete product. On the other hand, hot air in the lengthwise hollow part 6 can be led into a living room, by composing the hollow 6 being connected to the living room 7A at an exhaust outlet part 7B and a draft inlet part 7C. As a result, more than a half quantity of heat that is going to escape from a collective stack body can be recovered.