Without proper draft, the operation of a fireplace and stove, a heating gas, solid fuel boiler or column is impossible. Backdraft is an unpleasant phenomenon that gives residents great discomfort and is dangerous to health. If a chimney back draft is detected, you must immediately look for and eliminate the causes of its occurrence.
What is reverse thrust
The definition of reverse draft means a malfunction of the heating system and chimney. According to the laws of physics, all air masses without natural ventilation tend to go out where there is no resistance. In the presence of pipes and chimneys, the intensity of air movement increases. He starts to forcibly move. Chimneys are designed to create forced draft for the removal of combustion products from the premises.
When laying the stove and organizing the chimney, special engineering calculations must be made in order to create the correct direction of the air flow. The draft will occur due to the fact that the air pressure inside the oven and outside is different.
Causes of occurrence
Poor chimney draft can occur for various reasons.
- Blockages. Most often, the owners of stoves and boilers are faced with an obstruction of the chimney, which is formed due to blockages of pipes with debris or soot during long-term operation. It is strictly forbidden to make a chimney from pipes of different diameters. This will result in a quick smoke.
- Incorrect engineering calculations. When designing the chimney, errors were made in the calculations. For example, when using a powerful stove, a narrow chimney is installed. Because of this, a large flow of combustion products does not have time to go outside.
- An error in calculating the length of the pipes, which will lead to an insufficient pressure difference. The most optimal pipe height should be at least five meters.
- Improper ventilation. If the room is completely absent or is improperly equipped with ventilation, this will lead to a lack of the required volume of air flow.
- Accumulation of soot in the smoke ducts. This is a common problem that can be solved by regular cleaning.
If the roof ridge is installed above the chimney, the draft will overturn in strong wind gusts.
Determination of the presence of reverse thrust
The reverse draft in the chimney is also called "overturning". Air masses do not pass through the chimney, as it should be, but back into the house. This is a hazardous phenomenon that can lead to fire and severe poisoning with toxic gases.
To avoid negative consequences, it is recommended to always check the draft before starting the heaters. There are many ways to identify a violation. This can be done with simple folk methods:
- Light a candle, insert it into the furnace and observe the flame. If the light is directed inward, then the thrust is normal. If it remains in place and does not move, this indicates that there is no circulation of air masses.
- Bring a thin piece of paper or ribbon to the edge of the pipe. If they stretch into the sleeve, then the chimney is functioning correctly.
- The check can be done with a simple mirror.It must be brought to the chamber in which the fuel is burned. If moisture appears on the mirror surface, this indicates that combustion products do not come out.
- The color of the flame in the oven may indicate that the air is not circulating properly. If the flame is bright orange, this indicates a violation. With the right pull, it will be yellow-gold.
Checking the correct draft in the chimney can be carried out using special devices. The measuring equipment allows you to get the most accurate readings in pressure units. Parameters from 10 to 20 PA are the norm. Measurements must be taken from two sides: at the base and at the top of the chimney. But this technique is rarely used in private homes or apartments.
Ways to solve the problem
If the phenomenon has arisen due to a blockage, it is enough to remove the accumulated soot, clean the chimney. There are also many ways to deal with the malfunctioning of the chimney.
Deflector
The installation of a deflector can help in solving the problem of impaired traction. It is mounted on the top of the chimney. The device is designed to create additional thrust using the force of the wind. Deflectors are a wide range of devices that are designed to improve traction. Thanks to them, the risk of combustion products getting back into the room is reduced.
The deflector is designed to perform a variety of functions:
- increased movement of air masses in the pipe;
- protection of chimney channels from blockages, snow and rain;
- extinguishing sparks that arise due to incomplete combustion.
The operation of the device is based on the laws of physics. In the process of gas movement through the pipe, a vacuum occurs, since the pressure of the flow on the pipe walls decreases. The deflector is designed to artificially create such a vacuum. Gases falling into such conditions are removed by means of a draft from the pipe.
The most commonly used deflector is Grigorovich. For its manufacture, aluminum, galvanized and stainless steel are used. Copper can also be used, it does not corrode. But such a device would be expensive.
Deflectors allow to increase traction efficiency by more than 20%. In addition, the device improves the overall performance of the heating system. Thanks to the deflector, the fuel completely burns out, the level of heat transfer increases. In this regard, the devices are very popular.
The deflector consists of an upper and lower cylinder and a pipe connecting them to each other. A protective cap and brackets are installed to fix the parts. Not all models have an upper cylinder. This is an optional item. If it is absent, the device will consist of a lower cylinder, which is installed on the outlet pipe, two caps (forward and reverse), and a diffuser designed to dissect the air.
Deflectors differ from each other in the material from which they are made, in appearance, as well as in sensitivity to air flows. You can purchase a classic model or modern unusual designs, for example, in the form of a weather vane.
Stabilizer
The most effective way to eliminate the violation of draft in the chimney is to install a reliable stabilizer. This is a modern device with automation. It turns on when the movement of air masses is disturbed in the pipe. As soon as the pressure is completely normalized, it switches off automatically.
The device is an umbrella-like expander. It is installed on the chimney. Under the umbrella there is a section for the flow of air masses from the outside. A special temperature sensor monitors the temperature of gases that rise up from the firebox. If the draft is disrupted, the sensor begins to overheat due to accumulated gases. At this moment, the inclusion is triggered.
Increasing the length of the pipe
Often, draft problems arise if a non-professional was engaged in the design of the chimney. Incorrect calculations lead to insufficient pressure in the system. If the upper edge of the pipe is too low, there are many bends in the chimney, too short a pipe or narrowed passages, all these defects must be eliminated.
Each heating device needs a separate chimney. You cannot display several structures through one system.
Rotary turbines
One solution to chimney draft problems is to install a turbine. It is equipped above the chimney head. The wind will cause the turbine head to rotate. The movement always takes place in the same direction. This creates a vacuum over the smoke channel.
The downside of this method is its inability to work in calm weather. The turbine completely eliminates the possibility of debris or precipitation entering the chimney.
Temporary reverse thrust
Occasionally, homeowners can experience temporary backdraft. Most often this happens if the heating structure is rarely used. For example, the stove is fired with wood only in winter. Cold air accumulates in the chimney, which does not allow combustion products to freely go outside. As a result, the smoke gets back into the rooms.
To get rid of the cold air in the chimney, it is recommended to pre-ignite plain paper. A couple of burnt sheets will help slightly warm up the air masses that will rise through the pipe. After that, you can start full-fledged kindling.
If the reverse thrust occurs regularly, the phenomenon cannot be ignored. It is necessary to find the cause and eliminate it as quickly as possible. Correct draft is a guarantee of efficient operation of heating structures and the safety of the residents of the house.
