Individual heating systems connected with a boiler of apartment buildings have the possibility of installing collective chimneys which gives you the opportunity of connecting more than just one boiler with the same system.
If your boiler is placed away from the facade, the collective concentric system is the best, which extract the exhaust gas and intake air supply through the same collective duct.
In this case the legislation allows a maximum of 10 boilers connected with the same collective chimney and maximum 2 boilers per floor.
This is considered as a balanced system since the air inlet and fume extraction are at the same point (the end element) and there is no pressure differences between them.
The diameter is changing depending on if its over pressure or negative pressure. If you have over pressure the diameter will be smaller, one need security systems to prevent the gases enter the boiler or the heater which doesn´t work.
In such cases the triple wall (SET) chimney is the best which has insulation between the duct and the entrance of air in places where the temperature is very low (some degrees under 0ºC) to prevent the freezing of the condensate in the chimney duct.
If the condition is not that cold you can perfectly use the double wall concentric system without insulation (SED).
Collective, modular, concentric, double wall chimney for apartment buildings
Collective modular concentric triple wall chimney for the smoke and gas exhaust of combustion products