Back draft in the chimney - what does it threaten? How to improve chimney draft: where does reverse draft come from and how to deal with it
To keep the house warm - you need to build a stove, fireplace or install a gas boiler. And so that the fire in the hearth always burns cheerfully, the room is cozy and the air in the house is clean, you need to take care of the chimney equipment. The design and construction of smoke extraction systems must be treated with due attention, and not left for last, otherwise various unpleasant surprises are possible.
The purpose of chimneys - removing combustion products and creating draft in the furnace - only seems like a simple job. In fact, this is not an easy job - after all, the chimney has to constantly withstand the frantic onslaught of fire and smoke. And the task of building it correctly is not at all as simple as it might seem. Although over the centuries people have mastered the intricacies of taming fire well, the chimney remains one part of heating system, the construction of which must be approached very responsibly. Improper operation of chimneys can lead to a house fire or carbon monoxide poisoning of its inhabitants. Especially a lot of trouble is fraught with a chimney built in the old fashioned way by a self-taught master, in combination with modern systems heating.
Advice
The right choice turns the operation of the chimney into a safe and carefree process, and also guarantees the most complete combustion of fuel, provides ideal draft, resists the effects of condensate and aggressive acids.
Traction Secrets
The principle of operation of the chimney is based on draft - the ventilation effect in furnaces, which occurs due to the difference in air temperatures outside and inside the chimney. With an increase in this difference and the height of the pipe, the effect increases. Often, air is sucked in with great force through the ventilation holes in the stove door, creating real fiery whirlwinds in it. The density of warm air is less than cold air, which leads to a pressure difference inside and outside the pipe. Since the house where the stove is located is not airtight, due to the pressure difference at the foot of the building and the top of the pipe, an air flow is directed inward. In this case, warm smoke exits through a chimney at the top of the building, and cold air enters through the inevitable cracks at the bottom. There is natural ventilation. Thus, the stove is not only a source of life-giving heat, but also a means of providing ventilation for the building. Back in the recent past in the countryside and small towns stove heating was the main type of home heating and correct device stoves have received serious attention. Until now, in places where there is no gas, the stove for heating and cooking in the house is as important as it was many years ago.
The draft of the chimneys depends on the cross-section of the channel and the height chimney. There is a special table of sizes of smoke channels. For example, to create a normal draft in the fireplace, the cross section of the exhaust shaft must be at least 1/10 of the area of the inlet of the furnace. On the other hand, an excessively large cross section of the pipe also reduces thrust: the gases exit at a low speed and have time to cool, their density increases, and thrust drops. To improve combustion, it is customary to increase the height of the chimney, but to a reasonable limit, since the higher the chimney, the more resistance the flue gases experience. When constructing stoves and fireplaces, the height of 5 m from the level of the grate is considered optimal. This should be enough to provide reliable traction at any time of the year in all weather conditions. However, excessive thrust is economically disadvantageous, as it leads to accelerated combustion of the fuel. It is affected not only by the height of the pipe, but also by its length - after all, when laying a chimney, it is necessary to construct horizontal sections. Therefore, it is recommended to increase the height of the chimney by 1 m for every meter of horizontal pipe section. At the same time, the length of such horizontal sections should not exceed 2 m, since soot accumulates in them and the chimney draft decreases. If the size and shape of the room allow, it is necessary to move from horizontal to sections with a slope of 45 degrees - this reduces aerodynamic losses and increases thrust.
Ideally, for the efficient operation of the chimney system, each stove should have a separate flue gas duct. It is undesirable to connect two furnaces to one flue channel. This is done in exceptional cases and only as a necessary measure. But if you can’t do without it, then the following rule is observed: the distance between the connections of solid fuel furnaces must be at least 0.75 m, and for gas-fired ones - 0.5 m. After all, if several furnaces are connected to one chimney, the conditions their work may vary. The higher the smoke channel, the stronger the draft, and this can be a significant disadvantage if the stoves are located on different floors. With simultaneous combustion, the draft of the lower furnace will be much stronger, which will serve as an obstacle to the free exit of gases from the upper furnace. As a consequence, the top oven may have poorer draft, resulting in smoke in the room.
Today, modern cottages are rarely heated by stoves, they are successfully replaced by various boilers. But thanks to fashion, fireplaces have become an integral part of country house. And if it is planned to build two fireplaces in one house, for example, one on the first floor, the other on the second, then it is better for everyone to have their own separate chimney. The use of a common chimney is permitted only in exceptional cases and provided that the fireplaces connected to it are owned and controlled by one owner, and even then with many reservations.
When building a house and laying stoves, it should be remembered that the smoke and ventilation ducts are made separate and must be of high quality, that is, without cracks and bumps in the trunks. The exhaust products of combustion from one furnace must not enter another flue or ventilation duct.
Advice
The configuration of a metal chimney can be different: from the so-called "straight flue", to a complex design that allows you to bypass load-bearing elements ceilings and roofs. A brick chimney, as you know, is exclusively vertical.
Design features
Before laying the stove or installing the boiler, you should first decide how to arrange the chimney and where to install it. There are three main types of pipes - first of all, this classification refers to brick chimneys. According to the place of their installation, chimneys are divided into root, mounted and wall. The root chimney is installed on its own foundation in the form of a separate brick riser. The root pipe can combine several furnaces located on the same level. Mounted chimneys rest directly on the stove, preferably not on brickwork, but on a ceiling made of reinforced concrete slab with a thickness of at least 50 mm. In this case, you can repair the stove without disassembling the entire structure.
In rooms with solid walls, wall chimneys are most often installed. They are economical and convenient, as they are laid out along with the walls, often next to the ventilation ducts. It is not allowed to use a common wall chimney for two stoves installed on different floors, since the stoves have different draft, which depends on the height of the smoke channel. Therefore, with simultaneous firing, the lower furnace will have a stronger draft, thereby worsening the operation of the upper one, which will smoke and suffocate. The wall chimney must not be laid on clean cement mortar. It is very dense and does not let air through. Soot particles will settle on the cement joints with the formation of streaks, which may later appear on the outside of the wall. Therefore, it is better to lay out a wall chimney on clay-sand or lime mortars.
Chimneys are best located in the inner walls of the building. Passing through the channel, the smoke gives off its heat to the walls, which can serve as an additional source of space heating. If the channels are located in the outer wall, then the gases are cooled down due to the low outside temperature. This negatively affects the traction force in the furnace. In addition, tarry substances are released from the gases, which are deposited on the walls of the chimney. Sometimes these deposits can, having penetrated through the masonry, appear on the outer walls of the building. Therefore, chimneys are located in the outer walls only in exceptional cases. In addition, when the riser is mounted against the outer wall, it is necessary to increase its thickness. The most economical and expedient method of arranging chimneys in the main brick walls simultaneously with the construction of the house.
Sometimes in the layout of the house, the stove is not located against the wall, but in the middle of the central room. In order for the smoke from the furnace to enter the chimneys of the inner wall, a reversible sleeve is mounted, the length of which should not exceed 2 m. It is preferable to combine smoke risers into one array, in this case one chimney is laid out on two or three chimneys. The construction of one ventilation duct is mandatory.
Choosing a place to install a chimney on the roof of a building is also not an easy task. If the chimney is located below the roof ridge, the draft will depend on the direction of the wind, and vortices behind the roof will reduce the draft of the chimney. To solve the problem, it is necessary to build up the chimney so that it is higher than the ridge. Here, too, there are certain rules, and the height and diameter of the pipe not least depend on the height of the slopes and the shape of the roof.
The arrangement of chimneys depends on the design of the furnace, its location and power. Depending on these primary indicators, decisions are made on the structural arrangement of floors and walls located near the furnace. To ensure good traction of the pipe and clean its inner surface from soot, which is often the cause of fire, a special hole is made in the pipe wall for cleaning it.
Advice
In order to prevent the spread of fire to other floors, in the event of a fire outside, the chimney must remain statically stable for at least 90 minutes. At the same time, it is impossible to prevent the transfer of heat along the outer shell of the chimney and the increase in the temperature of its surface on other floors to dangerous values.
Difficult choice of materials
Chimneys are constructed from solid ceramic (clay, red) bricks, asbestos-cement or pottery (ceramic) pipes, metal and heat-resistant concrete blocks. The pipes used to remove the products of combustion of fuel have a significant advantage over stone-lined chimneys. Their inner surface is smooth, which provides minimal resistance to the movement of the gas flow and helps to reduce soot deposition. In addition, this design often surpasses brickwork in terms of service life.
The choice of a specific material and design depends not so much on the architectural style of the house, but on the type of stove, fireplace or boiler from which the smoke is removed, and the type of fuel used. The consequences of an incorrect choice of a chimney can be very different - a failure of draft and unstable operation of the combustion unit due to incorrect selection of the section, geometry or type of chimney; smoke in the living quarters and possible carbon monoxide poisoning due to non-compliance with construction and installation standards, and even a fire.
For example, brick pipes, until recently the most common, are poorly combined with the features of the operation of modern heating boilers operating either on gas or liquid fuel, or combined. These automated boilers operate, as a rule, in "transitional" modes - starting, heating the coolant to a predetermined temperature, then stopping and starting when the coolant temperature drops. This mode of operation of the boiler leads to constant temperature drops in the chimney. In addition, when using them, much more water vapor is formed than when burning, for example, firewood. And this radically changes the living conditions of the chimney. Condensate (steam deposited on the walls of the upper part of the chimney), combining with the products of combustion of fuel in the boiler, forms aggressive acids or mixtures thereof. These processes lead to a strong and rapid destruction of chimneys, the formation of microcracks and the penetration of flue gases from the boiler into the living quarters. After the formation of cracks in the chimneys, the process of their destruction proceeds like an avalanche and causes concomitant destruction of the interior finish.
Advice
Chimneys and ventilation ducts must be kept in good working order at all times. To do this, there are regular preventive maintenance, inspection and cleaning of the walls, which will prevent the occurrence of extreme situations.
Chimney system made of stainless steel with an internal ceramic pipe can be installed in country house after completion of construction work and does not require any additional finishing. In addition to its technical purpose, it is a compositional element of the interior.
In cottages with a large living area, where a powerful boiler equipment, signs of destruction of brick chimneys during continuous operation may appear after 13 years, depending on the type of fuel used. In addition, in brick chimneys, it is usually difficult to ensure a smooth channel surface, as a result of which soot settles on the irregularities, which over time reduces the chimney's aerodynamic cross-section and draft. Despite all of the above, brick chimney still relevant, for example, when burning solid fuel(firewood is used to heat fireplaces and sauna stoves, coal is used for boilers adapted to it). Moreover, brick traditionally goes well with the architectural appearance of any building.
Corrosion-resistant stainless steel inserts, made for the existing chimney channel, help to avoid negative phenomena. The installation of the inserts is carried out using a high-temperature sealant, which ensures complete insulation of the chimney. The very smooth surface of the inserts makes it possible to increase the draft of the chimney with the same section, which favorably affects the operation of the boiler room equipment. In the case of a pipe passing through residential or fire hazardous premises (attics or attics), double-walled chimneys with sandwich-type thermal insulation based on fiberglass or basalt insulation are usually used.
A good alternative to brick are ceramic chimneys. They are lighter, have smooth walls, have an almost perfect smoke channel shape, are easier to assemble, do not require as much insulation as metal pipes, provide absolute fire safety and are suitable for all types of fuel. At the same time, ceramic is a high-quality material that is resistant to high temperatures, insensitive to condensed moisture and acid. Ceramic chimneys are suitable for all types of fuel and are characterized by a long service life, in which they have no analogues.
Schiedel UNI is a universal chimney system suitable for all types of fuel and all types of boilers. It has a three-layer construction: high-quality ceramic inner tube, perfectly fitted insulation and lightweight concrete stone shell.
Asbestos-cement pipes significantly increase the strength and durability of the entire structure. Sometimes prefabricated pipes are used. They, together with prefabricated furnaces, are mounted on a cement mortar from individual blocks of heat-resistant concrete directly on site. Prefabricated pipes, depending on the design of the building, are installed as separate risers or built into the walls of the room.
In terms of mass application, the number of design options and the number of manufacturers, steel modular structures are far ahead of other types of modular chimneys. They are of three types: single-walled, made either from heat-resistant stainless steel or from enameled unalloyed steel; double-walled (double-circuit, insulated - with a layer of insulation between the outer and inner contours, which plays the role of a heat insulator); flexible (in the form of a corrugated hose).
Steel chimneys have many advantages. They are not afraid of exposure to condensate, they can be mounted inside existing chimneys, as well as inside and outside the building as a free-standing structure. They are produced in a fairly wide range of sizes according to the inner diameter of the smoke channel and the thickness of the pipe material, which allows you to choose the right option for the furnace of any system. They are relatively light, so they do not require a special foundation, provide high installation speed and are very decorative. Of course, it is not without drawbacks: the tendency to transmit noise, low self-supporting capacity. It is also important that high-quality steel is used in the manufacture of the chimney. However, this is easy to determine when buying - suppliers of quality chimneys usually give a guarantee of a 10-year service life.
Text: Victor Beskrovny
Consultant: Schiedel Chimney Systems
"Country construction", No. 2 (30), 2008
It depends on the traction force, on the rarefaction of the air. If there is cold air in the pipe, it prevents the combustion products from passing upwards.
Airlock cold air in the pipe is formed for various reasons: due to low atmospheric pressure, high humidity, strong wind, low pressure indoors.
Visually, the thrust force is determined by the color of the flame. If the flame is red, with dark stripes, then there is not enough air for combustion and, accordingly, the draft is weak. If the firewood burns bright white and there is a hum in the chimney, it means that there is too much draft. normal force traction corresponds to the yellow color of the flame, straw hue.
In order for the stove to flood quickly and without smoke (especially in winter or windy times), you just need to warm up the pipe to remove cold air from it: burn two or three newspapers rolled up into a tube closer to the chimney so that warm air rises up the pipe .
Calculation of thrust in the furnace
where: Q = smoke draft/draft flow, m3/s A chimney section, m2 (constant in height) C = flow factor (usually taken from 0.65 to 0.70) g = free fall acceleration, 9.807 m/s? H T i = average temperature inside the pipe, K T e = outdoor air temperature, K
No draft in the furnace Why?
If there is no draft in the furnace, then it is necessary to consider several options for improving it:
1. Weak draft due to cold pipe.
The pipe can be warmed up with a lit newspaper, as mentioned above.
2. Short pipe.
A short pipe may cause insufficient draft. The calculation formula shows that the traction force is directly proportional to the height of the pipe, so you need to immediately take care that the pipe is high enough.
The furnace is recommended to be placed indoors in a place that is located next to the ridge, so that when the pipe is brought to the roof, it is as close as possible to the ridge. If the outlet of the pipe on the roof is 1.5 m from the ridge, then the minimum height of the pipe above the ridge should be 0.5 m. If the pipe is at a distance of 1.5 - 3.0 m, then the pipe can be brought to the same height as the ridge.
Poorly chosen location of the furnace in the room and a short pipe greatly reduce the draft force of the flue gases. And even their reverse movement is possible, which is why the furnace begins to smoke.
If the height of the pipe meets the standards, increasing it will definitely increase traction.
3.Small section of the pipe.
The cross section of the chimney must be at least 125x125mm or pipe diameter not less than 125mm.
If the cross section of the chimney is small and the doors are large, then try to check the proportionality of the cross sections of the chimney and the oven door: put a brick in the door opening and, if it stops smoking, then you need to make another pipe with a larger cross section.
The ratio of cross-sections of openings, such as a blower, a firebox, a chimney, should be approximately in the proportion of 1: (4-5) : 2, respectively. Check these figures in your oven.
4.Low outdoor temperature.
The part of the pipe located in the attic and on the roof must be insulated so that it is not cold. If there is no draft with a non-insulated pipe, the furnace does not flood in any way, then this is due to the fact that the cold air column in the pipe prevents hot flue gases from escaping. Thrust can be created by throwing something lit into the chimney from above, thereby raising the temperature of the air.
5. Clogged pipe.
The pipe may be clogged with tar or soot. It needs to be cleaned from time to time. From the resin, the pipe can be cleaned by flooding the stove with aspen wood.
6. The draft in the pipe is highly dependent on the direction and strength of the wind.
If the wind moves horizontally with respect to the pipe, then when it hits it, it changes its direction upwards towards the outlet of the pipe. This causes the air to be rarefied at the outlet and the draft increases sharply.
When the wind blows from the bottom up, the thrust becomes even stronger.
If the wind blows from top to bottom, then it blows the smoke back into the chimney.
In order to prevent the wind from negatively affecting the traction force, a galvanized steel umbrella is placed on the pipe head, which prevents the wind from blowing directly into the pipe.
7. The absence of a protective cap.
If there is no umbrella on the pipe, then this leads either to dampness of the pipe, or to the effect of “slamming” it with the wind. It is necessary to install it.
How to improve traction
Poor draft in the chimney of a sauna stove is a shortcoming that must be urgently eliminated. If you have eliminated all of the above reasons, but there is still no traction. How to improve traction?Strengthen traction is possible by installing a deflector on the pipe. The deflector is the same cap (umbrella), only of a special design.
When the deflector is installed, even with the wind blowing at an angle, from top to bottom, or from bottom to top, anyway, the draft increases, and it is very noticeable, especially in indirect chimneys.
Chimney draft
thrust The chimney may be different, depending on the correctness of its dimensions and installation. But, extra traction is also useless: the firewood will quickly burn out, and the heat from their combustion will be blown into the pipe. You will end up with too much firewood consumption. Everything must be calculated in advance: the cross section and height of the pipe in accordance with the above optimal parameters. When the stove is fired, draft can be adjusted by changing the air flow: by closing or opening the blower door or damper.
Excess traction in the pipe is a much better option than none.
If mistakes were made when designing a residential building, in the future, such an unpleasant phenomenon as reverse draft in ventilation may appear. The effect develops if the shafts and channels were cast in solid panels. Ventilation is disturbed and brings a whole bunch of unpleasant odors to the side of the room. To eliminate this problem, a plug is usually used in an apartment - it cuts off air flows and redirects them to a common shaft.
Examination of ventilation systems
To identify problems, independent specialists are invited to check the ventilation system and its compliance regulations. Evaluation of effectiveness implies the use of an integrated approach. Specialists must describe in detail all existing deviations in the system performance, draw a general conclusion and give recommendations to the customer. The review includes three stages:
- Detailed review of all existing project documentation regarding ventilation and climate systems. At the first stage, specialists must evaluate the rationality of using the equipment, the relevance of its operation, and also check the compliance of design documents with state standards.
- Examination of installation work of ventilation systems. At the next stage, it is necessary to carefully check the quality of the installation of air ducts, channels and other equipment.
- Search for breakdowns and shortcomings, checking the current state. After a preliminary check, experts evaluate the performance of the system as a whole.
When determining the causes of ventilation failure, experts must measure the air parameters in the apartment, determine the places of unauthorized blocking of natural ventilation channels using a video endoscope, and compare the air flow rates with the design data.
Causes of reverse thrust
Ventilation in an apartment may not work properly for many reasons. Some of them can be identified immediately after inspecting the fireplace or stove. To understand why the thrust is broken, you first need to study the location of the pipe. You should also pay attention to its exit to the roof. If the initial inspection did not give results, you need to look for other reasons for the violation of ventilation in the apartment.
Most often, ventilation works in the opposite direction due to improper air flow into the room. The problem can be exacerbated by airtight windows. They are made from modern types of plastic and double-glazed windows - materials are strong and durable, but completely impervious to air. An alternative would be to install wooden windows. In European countries, this issue is solved with the help of supply valves and the installation of a ventilation system.
For the correct operation of the fireplace or stove, air must flow towards the room, since the ventilation ducts work much more actively than the chimney. In pipes that have a small cross section, the air temperature rises more quickly, and it rushes up.
Another reason for the formation of reverse thrust in an apartment or cottage may be the presence of stairs in the building. In fact, it is a huge pipe that can change the direction of air flow even in ventilation ducts. A curved ladder has less impact on the system than a straight ladder.
Also a factor in the violation of ventilation is a kitchen hood. If the kitchen is located close to the fireplace, back draft is possible. The latest models are capable of processing up to 1200 cubic meters of air per hour, which leads to the failure of the fireplace network and air outlets.
The most common causes of reverse thrust include:
- specific pipe location. If it is located in the area of the wind shadow formed by the protruding parts of the house, there may be a violation of air circulation.
- Wind that blows in a certain direction.
- Accumulation in the ventilation ducts of a large amount of cold air and vapors that impede the movement of the draft.
- Clogging of ventilation ducts with snow and ice.
- Accumulation of debris, formation of bird nests and soot deposits.
- Drafts that blow inside large rooms that are not divided into compartments.
- Incorrect operation of exhaust systems, compressor equipment and fans.
Air regulation optimization
To understand why reverse thrust occurs, it is necessary to analyze all the components. Such environmental factors as atmospheric pressure, humidity, the activity of convective currents, the presence of isotherm and inversion can disturb the balance of ventilation.
One way to solve the problem is to install a deflector - a mechanical fan that sucks smoke from the chimney shaft. The damper can act as an amplifier in the chimney - with the help of it, the reverse draft is regulated. Usually they are installed in the chimney channel and in the oven door. Sometimes the issue is solved very simply - just open the doors and ventilate the room.
Often this problem occurs if the stove or fireplace has not been used for a long time. Heavy air can accumulate inside, which impedes movement, and smoke is drawn through the fireplace towards the room. If the phenomenon occurs periodically, a chimney draft stabilizer will help to cope with it - it optimizes the movement of air in the ventilation. Safety valve protects against sudden pressure drops.
As a preventive measure, it is necessary to clean the chimney from time to time and install a special tee for cleaning. Use the following troubleshooting steps to troubleshoot:
- Removing the pipe above the wind shadow zone.
- Creating an influx of fresh air currents.
- Channel cleaning.
- Clearing frozen areas from snow and ice.
- Changing the layout of the room, creating organized flows and installing doors.
Violations in the ventilation of apartment buildings
Back draft in the apartment leads to fogging of windows, the appearance of dampness and unpleasant odors. It can also lead to the development of such dangerous diseases as bronchial asthma and many other respiratory diseases.
If there are concerns that the ventilation is faulty, there are several ways to check this. You should open the window, take a sheet of thin paper and bring it to the ventilation grill. If the air flow attracted it, then there is no problem, if it does not hold, the ventilation is broken. You can also use a lighter or a lit candle - the flame should bend to the side. In hot weather, the air becomes heavier, the wind does not blow, so it is not worth checking at this time.
The owners of the apartments do not have the right to clean the ventilation shafts on their own. To do this, they must call specialists. Residents can only remove the grate and try to blow off debris with a vacuum cleaner. If this does not help, it remains only to turn to professionals.
One of the reasons for the appearance of reverse thrust in the apartment may be unauthorized redevelopment of neighbors. During repairs, they can block the ventilation stack and create a negative microclimate and unpleasant odors towards adjacent apartments.
To improve ventilation, air conditioning and specialized supply valves are used. Power is calculated based on the size of the apartment. In the case of installing a supply ventilation system, you need to consider the sound insulation of the system. The device can be hidden under a false ceiling or mounted in walls.
AT apartment buildings the problem often appears on the top floor. This is due to the peculiarities of the ventilation. For normal circulation, air must pass at least two meters towards the roof. On the top floor, this is difficult, so modern methods are used to remove excess air. To do this, increase individual channels.
The comfort of living in a house or apartment depends on the quality of ventilation. Excessive humidity creates an unhealthy stale atmosphere. Dealing with this phenomenon on your own is quite difficult. Therefore, in order to figure out why ventilation does not work, it is best to contact qualified specialists. They will identify the causes of the malfunction and offer an individual solution.
The directional movement of combustion products along the flue ducts is a fundamental factor for the efficient and safe operation of almost all heating devices. There is a movement of air masses in the chimney with a difference in pressure, temperature and density between the air in the chimney and the atmosphere. The warm air in the chimney has a lower density and tends to rise, and colder air masses take its place.
But there is such a thing as backlash. The manifestation of this effect is immediately visible to the naked eye - the smoke from the combustion of fuel does not come out as it should go into the chimney, but moves into the room, which creates the danger of poisoning a person with combustion products and carbon monoxide. Why there is a reverse draft in the chimney and how to deal with this phenomenon, we will consider in this publication.
Reasons for this phenomenon
Reverse thrust, as it became clear from the above, there is a consequence and there may be several reasons for this. And above all, the main reason for poor draft in the chimney, and, accordingly, the appearance of this effect, is the incorrect design of the heating system and non-compliance with the rules of application. building materials for the arrangement of the smoke exhaust system. Among other reasons, the most common are:
- Banal clogging of the chimney.
- Incorrect calculation of the cross section of the chimney.
- Failure to comply with the height of the smoke exhaust system.
- The presence of horizontal and narrow sections in the smoke ducts.
- The location of the chimney in the zone of "wind backwater".
- Incorrectly organized ventilation system of the room and insufficient supply air.
But it often happens that the phenomenon of reverse thrust occurs suddenly, on previously normally working equipment. This may be due to adverse weather conditions such as strong winds, fog or heat outdoor air in summer. Each of these reasons is able to reverse the direction of movement of combustion products, thereby stopping the normal process of smoke removal from heating devices.
How to determine insufficient draft in the chimney system
If the reverse draft is visible to the naked eye, then poor draft in the chimney should be determined, and this must be done before each start of the heating appliances. To do this, several basic methods are used.
Advice:
If the draft in the chimney suddenly disappears, then, first of all, the cause of what is happening should be determined. A visual inspection of the flue duct is the first thing to do. Often, you just need to clean the chimney, and the effect of reverse draft in it will disappear.
Back draft and ventilation
Many users of stoves and fireplaces, especially after repairs in the house, say that: “There was a reverse draft in the chimney, what to do about it.” Everyone is immediately interested in solving the problem, but few people thought why it was after the repair in the room that this phenomenon appeared.
Very often, the effect reverse thrust appears precisely in houses with installed plastic windows and high-quality doors. Most often, when replacing windows and doors, the owners of the premises do not think that after such alterations, the normal functioning of the ventilation system ceases.
Oddly enough, the appearance of this effect is directly related to ventilation, or rather, to its absence. Warm air has a lower density and therefore tends to rise. Warming up in heater, air masses rise through the chimney, and colder air rushes to its place. But in the process of work, it may happen that a low-pressure area will gradually appear in the sealed room and the vacuum will become so strong that it will begin to draw fresh air from the chimney, “overturning the draft”, and turning the movement of smoke in the opposite direction. The better the draft in the chimney, the longer the effect of the reverse movement of combustion products will not be, but without a sufficient amount of supply air, this process is inevitable.
In order to solve this problem, it is necessary to organize the flow of air masses from the street. This can be solved in several ways:
- By creating an influx of air masses through loosely closed windows, doors or vents.
- Installing inlet wall valves.
- Mounting supply valves on PVC windows.
Each of these measures will contribute to the penetration of outdoor air masses into the house, preventing a decrease in pressure in the room and the formation of a reverse draft effect. Which method to choose, it is best to consult a specialist.
Ways to improve the removal of combustion products
Keep in mind that even with the best ventilation system, smoke extraction will be ineffective if the flue ducts are clogged or improperly designed. With the wrong project, there is only one way to deal with it, disassembling the chimney and completely reworking it.
If there is a defect in the flue ducts that reduces the removal of combustion products, several devices can be used to improve this process.
Backdraft is a very dangerous phenomenon, and not only by the appearance of carbon monoxide in the living room, but also by sparking directed into the room. At the first manifestations of this effect, you should stop using the stove or fireplace, try to independently determine and eliminate the cause, and if this does not give a positive result, immediately contact the specialists.
Foreword
The concept of reverse draft in the chimney refers to the incorrect operation of the system heating device and the chimney as a whole. There are several reasons why there is a reverse draft in the chimney, you need to know about all of them in order to take competent actions to eliminate the malfunction.
Content
The concept of reverse draft in the chimney refers to the incorrect operation of the heating device system and the chimney as a whole. There are several reasons why there is a reverse draft in the chimney, you need to know about all of them in order to take competent actions to eliminate the malfunction. What to do with chimney reverse draft and how to eliminate reverse draft are issues that require the closest study of all stove owners.
Draft is an aerodynamic directed air flow of flue gases in any exhaust structure. This phenomenon occurs due to the difference in air pressure inside the furnace and outside.
Air masses always tend to go where there is least resistance. Therefore, a reverse draft in the chimney is formed when the flow of gases from burning wood does not go out through the chimney, but back into the room.
There is another term - "thrust rollover". In this case, the direction of movement of the air flow for a short period of time is reversed. One of the causes of draft problems can be nearby tall buildings or trees, as well as if the height of the chimney is lower than the roof ridge. In fact, there are many external factors.
The first sign of reverse draft is a large amount of smoke when wood is burned in the stove. At the same time, the glass on the door is quickly smoked, and when the door is opened, the smoke immediately enters the rest room. This already indicates weak traction. If you do not increase the draft in the chimney, then it can quickly turn from weak to reverse.
You can check the draft force in the chimney as follows. Using toilet paper, you can see exactly how it deviates. The direction of the smoke from the cigarette will also indicate the presence or absence of the correct draft. The hum in the chimney and the white color of the flame indicate too much draft. But the yellow-golden color of the flame is an indicator of good traction. Numerous devices are currently in use that measure chimney draft in units of pressure. With their help, measure the pressure at the base and at the top of the chimney.
Causes of reverse thrust
Firstly, the design of the chimney itself may be the cause of the back draft. Do too high pipe thrust is always stronger, and at low it is often insufficient. A little over 5 meters is considered the most suitable length, then problems with traction will occur very rarely and will definitely not be associated with the height of the pipe. In addition, the cross-sectional area of the chimney must correspond to the furnace.
With very small cross-sectional dimensions and at the same time with a powerful furnace, a large volume of combustion products simply will not find a normal exit, there will be no sufficient thrust. Also, too large a chimney can cause all the heat to go outside. Under no circumstances should pipes be installed near the chimney different diameters on the different areas. Otherwise, soot will form and traction problems will occur.
A big obstacle to the movement of smoke is the uneven surface of the pipe. Numerous deposits reduce the diameter of the pipe, and the furnace becomes more and more difficult to melt each time. Certain difficulties are created by the corners with the turns of the chimney. With the constant accumulation of soot in them, obstacles will be created.
To prevent this, when designing a chimney, standard norms should be followed: the outlet should be at an angle of 45 °, and the turn should be 90 °. Equally important is the shape of the smoke hole. The round shape is considered the most suitable for good traction, while the square and rectangular shapes can create problems. At these corners, additional turbulence is formed, which to a certain extent interferes with the overall flow and, therefore, reduces thrust. Most often, poor draft is observed in metal chimneys. Their problem is that they quickly heat up, but also cool down rapidly, and cold air always sinks down. That's why brick chimneys higher quality in this regard.
Backdraft can occur due to a violation of ventilation or its complete absence. It is necessary to check if there are drafts in the room. Intense air currents in the baths often appear due to the presence of stairs to the second floor. Therefore, you need to monitor the air flow and never open the windows on the site if it is located much higher than the level of the firebox.
Ventilation should also be given special attention in cases where there is a geyser. It draws air from the combustion room. After some time, there will still be a serious lack of oxygen and rarefaction of the air will be felt. Periodically, air currents will penetrate through the chimney, the column will start to go out, and the room will begin to smoke.
There are also external factors that affect the formation of reverse thrust. Smoke can enter the room due to high humidity outside or strong winds. It also happens when it's noticeably warmer outside than inside the house, so there's a pressure difference. If this is the reason, then you can feel the unpleasant smell of burning. In this case, you need to open the window and ventilate well, in addition, the temperatures will even out a little. It is extremely rare that the cause of the traction violation is the wind, which causes turbulence above the roof. In addition to this, the tip may still be directed incorrectly in relation to the roof ridge.
And finally, the location of the chimney plays an important role. In the inner part of the bath, it has a good effect not only on the heating capacity of the system, but also makes it possible to maintain good traction even in severe frosts. And an external chimney running along an outside wall takes longer to warm up and often condenses.
Temporary back draft in the furnace
Sometimes the reverse draft in the furnace occurs as a temporary phenomenon - only for a couple of days. This most often occurs after a long period of inactivity of the furnace or firebox during cool weather.
By this time, there is already accumulated heavy cold air in the furnace and in the chimney, which will immediately prevent the creation of draft, and smoke will enter the room.
If reverse thrust occurs periodically, then its cause must be established and eliminated. For safety, it is recommended to use a chimney draft stabilizer, which is a secondary air supply device for the optimal force of its movement of air through the chimney. The stabilizer has a safety valve that, in case of emergency, will prevent the occurrence of excessively high pressure.
You can get rid of cold air in the chimney after a long break in kindling using plain paper. To do this, you need to burn a couple of sheets, and slightly heated air will rise through the pipe and push out the cold. After that, you can melt the oven.
It is necessary to clean the chimney in time. And it is also desirable to install a pipe tee for cleaning. Then the reverse thrust will not bother.
Chimney deflector (with photo)
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Look at the photo: the chimney deflector is a mechanical fan that sucks smoke from the chimney shaft.
It is also necessary to see how the gate is located - a special damper with which the draft is regulated. One gate must be located in the chimney channel, and the second, as a rule, is located either in the furnace or in its door. You can try to change their position.
Modern deflectors for the furnace are:
with a flat top;
equipped with an opening lid;
having a gable roof with two slopes on the pipe;
with a semicircular top.
Deflectors with a flat top made of copper are often placed on baths in the Art Nouveau style.
For modern buildings, a cap with a semicircular top is most suitable. And a device such as a gable roof deflector best protects the chimney from snow.
Basically, sheets of galvanized iron are used for the manufacture of deflectors, although in recent times you can often find such deflectors on sale in which the metal is coated with enamel or even a layer of plastic.
Some models of deflectors must be inserted with the door towards the smoke box. To do this, you need to bring one edge to the wall, gently lift the second and lower it into place. For ease of installation, the plates should be dismantled from the rear and side walls.
In addition, there are two handles on the deflector, which are called "cold hand" and are designed to control the oven.
You can choose a model in the store, or you can easily make a deflector for the chimney yourself. Before making a deflector on a pipe, read detailed description stages of work.
Before proceeding directly to the manufacture of the deflector, it is necessary to determine the material from which it will be made. It can be copper, galvanized iron or stainless steel. Despite the fact that copper is a rather expensive material, it is better to opt for this metal, as it is resistant to atmospheric phenomena. This is due to the fact that the deflector is located in one of the most inaccessible places in the bath, and frequent repairs will be problematic.
Before you make a deflector, you need to draw on cardboard a scan of all the main parts, including a cap, diffuser and outer cylinder. Then you should transfer everything to the metal and cut out according to these patterns using special scissors. Next, you need to connect the parts to each other using rivets, bolts or welding. Brackets must be made from a strip of metal, with the help of which the cap will be fixed to the surface. A reverse cone should be attached to the cap. Having assembled the deflector on the chimney pipe, you can proceed to install it on the roof. First you need to fix the lower cylinder using bolts and nuts. Using clamps, you need to fix the diffuser on the lower cylinder, and install a cap with a reverse cone on it.
The device of the deflector-weather vane on the chimney for the furnace
There is a new popular type of deflector - a weather vane-deflector.
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It is (see photo above) a special device in which the body rotates simultaneously with the deflector visors curved on it. Such visors are connected to the bearing assembly. The weather vane, located in the upper part, allows the entire structure to always be located taking into account the direction of the wind.
The operation and arrangement of the deflector-weather vane for the chimney is quite simple and straightforward. The air flow penetrates into the space between the visors, accelerates and thereby creates a rarefaction zone. As a result, the draft in the chimney increases, the fuel in the furnace burns well, and the air exchange also improves.
You can also make a weather vane-deflector, after which the structure itself should be attached to the cut of the chimney using a ring with a bearing assembly. It is a stable influx of fresh clean air and high-quality removal of combustion products that is the key to the good operation of the furnace.
Rotary damper device for the chimney of a sauna stove
An important role in regulating the traction force is played by the gate device, which is a special horizontal plate, which, due to its position, increases or decreases the cross section of the chimney. There is a small hole in this plate, which does not allow the damper to completely seal the chimney. This is necessary to comply with fire safety regulations. Often a horizontal gate is mounted in brick ovens, but can also be installed in steel chimneys. Rotary, the chimney damper is a plate that is mounted along the axis. Its adjustment is made by turning. The only drawback is that welding burns occur at the rotary gate, and such an unpleasant phenomenon has recently been observed very often.
Both types of damper have certain differences: a chimney damper, i.e. a horizontal damper, allows you to adjust the flow area, and the throttle only shows whether the chimney is open or closed. In extreme cases, you can fix with a chain.
In order to choose the right damper for the chimney, you need to decide on the type of furnace and take into account some more features. The damper is installed, except for some new models, where the combustion process is already being adjusted by controlling the supply of fresh air, for which a deflector is used. AT gas oven it is recommended to use a rotary gate, which is able to completely eliminate the risk complete closure chimney, and the flame does not accidentally jump out through the ash pan. If a damper is nevertheless used, it must be ensured that there is always a gap of at least 30-40% of the cross-sectional area of the chimney. Rotary dampers for a bath stove with intermittent action should not be installed, because the damper always allows steam to pass in the closed state when it is supplied. But there is an opinion that when the rotary gate is in the open position, then the pipe located below is quite difficult to clean afterwards.
As a rule, the damper is sold together with the chimney, as it is an integral part of it. But you can also buy a gate at any specialized store. The main thing is to correctly determine its size.
Cast iron chimney damper
There are several options for gates, depending on the material from which they are made. Chimney valves are most often made of cast iron. But this material is quite heavy, and the installation of such a cast-iron gate is difficult. In addition, it can only be placed on brick ovens. For all its merits, the cast-iron chimney damper is heavy, so installing it yourself can be difficult.
Stainless steel chimney damper and damper
The stainless steel chimney damper is usually made with a thickness of 1 mm. Their advantage lies in the fact that they are able to withstand temperatures up to 900 ° C, have a special mechanical density and are resistant to corrosion. Steel is pretty smooth. It can additionally be polished to a shine, and, therefore, soot will not settle on such a gate. Another plus is that steel has good thermal conductivity. Such a valve is able to block the chimney by 85%, and carbon monoxide will be well removed.
The gate can be made and installed independently. As a rule, the damper is mounted in the chimney even at the stage of its construction. It should be located on the first meter of the chimney. This is necessary for ease of use. You just need to keep in mind that the area where the gate is located should not be insulated, otherwise it may jam.
The damper is a kind of initial part of the chimney, behind it the pipe itself already begins. The use of a gate is the easiest way to control draft.
Before making a gate, it is necessary to lay out the first brick row of the chimney. A fragment of the gate valve for the chimney is cut out in the second row. In one brick, you need to cut a groove for the handle. The main thing is to lay out the second brick row in such a way that there are no gaps in it. If gaps still form, then they must be filled with cement mortar. It is possible to install a chimney damper without fastening - it will hold only due to its snug fit to the structure. To properly adjust the draft, it is necessary to ensure the supply of air to the combustion zone. It must be remembered that with the gate closed, carbon monoxide will still seep into the bath, even if fumes and smoke are not noticeable. It is very dangerous! In a few hours, you can completely burn out. It is allowed to close the gate only at the very end, when everything in the furnace has already burned out and is slightly covered with ashes.