Vertical section of the furnace with rising and falling channels corresponding to the natural movement of the gases.

To heat the apartment stove evenly, combustion gases from the furnace should be distributed through riser and rainfall channels in accordance with the natural properties of the gases (for example. hot exhaust gases, one temperature, directed from the furnace upwards with two channels with the same cross-sections). If, for any reason, channel A is less hot than channel B, then the gas temperature in port A will also decrease accordingly, and the speed of movement of gases, as heavier it will decline, therefore, channel A will not heat up, but on the contrary it chilled. Conversely, in channel B, due to its higher temperature, the flow of gases will gradually increase (better string), and as the speed of movement of gases increases, the duct will heat up more.

Eventually, there may be a complete cessation of the movement of gases, in channel A and all gases will go to channel B, while in channel A, downward backward movement of gases may arise (shown in the figure by a dashed line).

It follows from the above, that hot, the cooling exhaust gas cannot be routed upward through several channels, but it is better to discharge them in one common stream.

Let us now consider the opposite example, where the exhaust gases of the same temperature descend through several channels.

If in one of the channels, e.g.. in channel A the temperature will drop for various reasons, and let the gases cool, then becoming heavier, they will start to fall faster, increasing the flow rate in channel A in relation to the flow rate of gases in channel B with a higher temperature.

Accelerating the falling rate of gases in channel A will cause, due to the faster inflow of warmer gases, their temperature rises until the temperatures in both channels are automatically equalized.

From the example above it follows, that the division of hot - cooling exhaust gases directed from the main-riser channel by several channels downwards is evenly divided into all channels.

Vertical section of a furnace with one channel and several downpipes.