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edit this page Chinese Chimneys by Zhu Zhao-ling et al.
The purpose of installing a chimney on a stove is to create a negative pressure in the chimney. This draws out the fumes (C, CO, CO2, SO2, etc) from the burning fuels to promote good combustion and avoid air pollution damaging the health of people in kitchens. [top] [end]Chimney design and construction Round section chimneys are usually made of sheet steel or concrete pipes, or built from ceramic sections. They are usually 60 to 150 mm interior diameter for domestic houses and steel is mainly used in South China. The diameter depends on the volume of the combustion chamber in the stove and the fuel type 60mm for coal briquettes and 90mrn for solid coal. Square section chimneys made from bricks are 240 to 360 mm inside.
The outlet from the stove to the chimney should be in the correct position and its size must be correct (figure 1). If it is too low, too much heat will go up the chimney and the stove efficiency will be low; if too high the smoke with enter the room from. the pot seat.  Figure 1: The distance between the bottom of the pot and the smoke exit to chimney |
[top] [end]Chimney position (figure 2) If the stove is in the middle of the room, the chimney will go through one side of the roof. If the stove is set into a back wall, or is for a fire bed, the chimney will be outside the house.  Figure 2: Chimney height and fire bed chimney |
[top] [end]Chimney height (figure 2) A chimney pipe through the roof must extend at least 200mm higher than the top of the roof. If the stove is near a wall, the chimney can be angled to go through the wall, but the top must still be above the roof top to prevent wind currents blowing down the chimney. A coal briquette stove does not need a chimney except when the fuel is being lit. Chinese coal briquettes are made with holes to make lighting easy. [top] [end]Factors affecting chimney draught - Chimney draught is in direct proportion to chimney height - too high gives too much draught, too low causes smoke in room, both cause loss of efficiency.
- Chimney draught is in inverse proportion to diameter - large diameter decreases draught velocity, small diameter increases velocity,
- Fume removal is in direct proportion to draught speed.
- Steel chimneys cause less surface friction than ceramic or brick chimneys, and so allow better draught.
- Chimney draught is in direct proportion to ambient air pressure, ie, low pressure decreases draught. (for example, when it is raining).
- A hot chimney gives better draught. A cold chimney causes poor draught and can cause smoke in the room.
[top] [end]Chimney installation (figure 3) When stoves are used for space heating the vertical chimney has a near horizontal section at the top slightly up from the vertical section, not down. Where chimneys have joints, the upper section should fit inside the lower to prevent water dripping on the floor.  Figure 3: Chimney pipe installation |
If the wind direction changes, it can force air and fumes down the chimney and into the room. This may contain carbon monoxide (CO), which is odourless and very poisonous even in small quantities, and can cause long-term, health damage and even death. Figure 4 shows the 'dog's nest' arrangement below the bottom of the chimney pipe which sends chimney down draught back up the chimney, rather than to the pot hole. It can also serve as a sump to collect ash etc. and should have an opening for cleaning.  Figure 4: Dog nest |
Every chimney needs regular cleaning to ensure good room ventilatior, correct draught and stove combustion, and to clear blockages or accumulations of tar which can cause fires. Blockages are likely to occur at joints, bends or restriction in the pipes. It may be necessary to remove a steel chimney or reconstruct a ceramic or brick chimney. Openings can be provided in the chimney to facilitate cleaning.
[top] [end]Contents: Boiling Point 34: Smoke Removal  . |
Smoke in the Kitchen - Any Stove Will Smoke if You Dont Use it Correctly - Acute Respiratory Infection, Conjunctivitis and Accidental Burns - Exposure to Air Pollution From Transitional Household Fuels In A South African Population - Smoke Removal in Kenya - Chinese Chimneys - Indoor Air Pollution in Rural Tigray - Removing Smoke from Nepali Kitchens - A Breath of Fresh Air for Smoky Houses - Vietnames Kitchens - Reducing Greenhouse Gas Emissions and Improving Environmental Degradation - Indian Governments Stove Programme in Question - Cooking energy Efficiency in Indonesia - Phillipines Ricehull Stove - Stoves for Cafes and Food Stalls - Fuel from Three Stages of Pyrolysis - An Electric Metad - Crack Reduction in Clay Stoves
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