Along with height very important correctly to determine the size and form of the chimney. In practice the narrow section of the channel meets very often, that limits a possible choice of fireplace designs or bad work of an existing fireplace.
On a question to builders: why this or that section or the form of chimney has been chosen you’ll often hear the Answer: “and we always do so…)”.
The section form and dimension of the channel, first of all, influence throughput ability of a chimney, which is on capacity of combustion gaseous products which can pass through this section for a time unit.
In the exact account of an internal friction of gases lets engaged it to gas dynamics scientists, and the expert should know, that in most cases speed of departing gases in a chimney, as a rule, does not exceed 16 feet per second, and the working open fireplace absorbs air from a premise with a speed about 2 feet per second on an input.