4 min 825

The chimney at first glance seems to be the simplest element of all housing construction. But this is only at first sight. Correctly executed chimney this is a rather complex engineering structure, on which the efficiency of the heating system, as well as the health and even life of the inhabitants of the house, depends. That is why everything calculationsrelated to the design, cross-section and height of the flue ducts must be carried out by professionals.


What is traction

Draft in a chimney is a physical phenomenon in which there is an independent movement of heated air filled with fuel combustion products. It occurs when the difference in temperature and pressure between the room in which the heating boiler, and atmosphere. It is worth saying that the quality and speed of exhaust gas outputin insheds more many factors:

  • Cross section of smoke ducts.
  • The design of the exhaust gas system.
  • Exhaust smoke temperature.
  • Direction and strength of the wind.
  • Season.
  • Chimney height.

Draft in the chimneyIn addition to these factors, the draft can be affected by the materials from which the chimney is made, the fuel burned in the boiler furnace, the air flow into the room with the boiler installed and etc. Changing any parameter can improve or worsen draft, making the heating system more efficient or significantly reduce her efficiency, increase or decrease fuel consumption.

The main influence on the quality of the output of combustion products is exerted by the temperature difference between the outdoor air and air masses in the room. This is due to the difference between density warm and cold air. Since the density warm there is less air, it tends to rise. This is what leads to the pressure difference inside and outside the chimney.

In boilers with different types of fuel, combustion takes place in different ways, and therefore the temperature of the smoke is different. For example, in gas boilers, the temperature of fuel combustion throughout the entire combustion cycle is almost the same. At high efficiency modern gas heating equipment and the temperature of the exhaust gases is quite low, often not exceeding 100FROM°.

In solid fuel boilers, combustion occurs at very different temperatures and is quite uneven: during the ignition of the fuel, the temperature of the exhaust gases rises sharply and reaches 600FROM°. After the boiler enters the operating mode, the temperature of the exhaust gases decreases. This uneven temperature performance also affects the draft in the heating system.

Influence of chimney length on draft

Theoretically, the higher the chimney, the better the output of exhaust gases. In fact, everything happens differently: going up the chimney, warm air masses filled with combustion products gradually pick up speed. But, rising, the gas begins to cool, therefore, an excessively high height of the chimney pipe can only worsen the removal of combustion products into the atmosphere.The formula for calculating the length of the chimney

The correct length of the chimney can be calculated using a rather complex formula, in which the dependence of draft on the length of the chimney duct, its cross section and temperature indicators inside and outside the room will be visible, volume gases formed during the combustion of fuel.

The correct design of the chimney for the boilerWe purposefully do not attempt to explain this formula by providing the opportunity to calculations specialized organizations.

Carbon monoxide is odorless, so if there is insufficient draft, it can enter the living room. With a sufficiently low concentration of carbon monoxide in the air, a person stops breathing and dies.

Smoke extraction systems for gas boilers

The height of the chimney for a gas boiler is determined by the recommendation of the manufacturer of heating equipment and the SNiP regulation, which establishes the following indicators:

  • Climb chimney above flat roof should be at least 1,2 m.
  • The pipe must rise above the roof ridge at least how on the 0,5 m. if it is located closer to the skate how on the one,5 m.
  • If the pipe is located from 1,5 m. before 3mto the ridge, then the chimney should not be lower than the level of the ridge of the building.
  • If the chimney is located further 3m. from the skatethen the height her must match the line carried out from the skate at an angle of 10° to the horizon.

the height of the chimney relative to the roof ridge is calculated based on many indicators. Above are average data for gas equipment. For more accurate calculation you should contact heating specialists or a specialized organization.

Chimney for solid fuel boiler

For solid fuel boilers, the length of the chimney is the most important parameter. If the length is insufficient, then the traction will be bad. Exactly this maybe in any momentnt prlead to her “tilting”, due to which carbon monoxide and other combustion products will penetrate into the room.

The required height of the chimney for a solid fuel boiler is mandatory prescribed by the manufacturer in the passport for the boiler and carefully calculated by engineers more at the design stage. That is why, in order to eliminate errors associated with independent calculations chimney, its length and minimum allowable diameter, it is best to use the factory recommendations.


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