According to National Standards of Ukraine B V.B 2.5-33:2007 “Engineering equipment of buildings and structures. Individual apartment heating of residential buildings with gas-fired heat generators with closed combustion chambers using collective chimneys and chimney systems,” the cross-sectional area of collective chimneys and general exhaust air ducts of chimney systems must be verified by calculation according to the methodology provided by the manufacturer of the collective chimney system.

It is done based on the total thermal capacity and the number of heat generators connected to the collective chimney, assuming they are operating simultaneously.

As of today, the methodology for calculating air-gas flue systems with multiple connections is detailed in the National Standards of Ukraine B EN 13384-2:2010 “Chimneys. Methods for thermal and aerodynamic calculations.”

The standard specifies that the aerodynamic and thermal calculation is applicable to collective chimneys serving buildings with a height of more than 5 floors, as well as to air-gas flue systems (AGFS) that can be installed in buildings up to 10 floors.

The main parameters that affect the calculation of the cross-sectional area are:

• Total effective height of the chimney;
• Number of connected boilers or heat sources;
• Nominal thermal power of each boiler or heat source.