Why there is back draft in the chimney and how to correct the situation

Vasily Borutsky
Checked by a specialist: Vasily Borutsky
Author: Elena Mezhenina
Last update: September 2019

A fireplace in your own home is the dream of any romance. Which of us didn’t try to find ourselves in a comfortable chair near our own little stove on a winter evening to blissfully absorb the heat spread by a living fire with our whole body.

But the smoke that fills the room and does not want to go into the chimney does not fit into this idyllic picture. Back draft in the chimney - this is the name of this unpleasant phenomenon. Why does it arise and how to deal with it? We have collected information about this for you and provided in this article.

We also paid attention to methods for checking draft in the chimney and examined in detail the best options for solving draft problems.

What is backdraft?

Before you understand the causes of this phenomenon, you should understand the essence of what is happening. The heating device installed in the house, together with the chimney, forms an exhaust structure.

The air pressure inside and outside the device is not the same. Because of this difference in pressure, thrust arises - an aerodynamic directed flow of flue gases.

Safe and efficient operation of the heating device implies that the combustion products will move from the burning fuel along the flue ducts. The air masses in the chimney have a lower density, as a result of which they tend upward. In their place comes cooler outside air. This is exactly what the change of flows should ideally be.

Visual manifestation of reverse traction
Backdraft is not only an unpleasant, but also a dangerous phenomenon, the consequences of which can manifest itself in a deterioration in the health of people and pets

But sometimes a phenomenon called reverse traction occurs. In this case, the smoke resulting from the combustion of the fuel is not directed out through the chimney, but into the room.

The occurrence of backdraft is not only unpleasant, but also a dangerous phenomenon. The penetration of combustion products into the room leads to serious poisoning, and carbon monoxide carries a mortal danger.

The first signs of failure during the movement of air masses can be not only smoke entering the room, but also a quickly smoked glass window in the furnace door. At first, the thrust may just be weak, but if you do not take action, over time it will become reverse.

Sometimes there is another phenomenon associated with the movement of smoke - the air flow for a multiple time changes its direction to the opposite. So there is a rollover traction.

Causes of Backdraft

There are several reasons for reverse thrust. The main of them can be considered errors in the process heating system design. Perhaps, during its construction, the rules for the use of building materials were violated.

A problem of this kind will not arise at all if the chimney is constructed in compliance with existing standards: the rotation must be done by 90 °, and the outlet should be placed at an angle of 45 °. Particular attention should be paid to the shape of the chimney section.

The most suitable shape is a circle. If angles are present in the structure, turbulence may occur which impedes the discharge of gases.

Chimney clogging
The profession of a chimney sweep, as you see, has not lost its relevance, but, with an increase in the number of private cottages, has even become even more in demand

If we compare brick and metal chimneys, the draft in the latter will always be less quality. The problem is that the metal heats up pretty quickly, but just as quickly it cools down. And cold air, as you know, goes down.

Frequently encountered include the following reasons why there is no draft in your chimney:

  • Chimney obstruction. It may well be that it is simply clogged with garbage or smoked as a result of prolonged use. Quick smoking can also occur if the chimney is composed of pipes of different diameters. In no case should this be done.
  • Errors in the calculation. Incorrectly calculated cross section for smoke passage. Quite often, when designing a design by non-specialists, imbalances arise in the sizes of the elements of the device: the combustion chamber and the chimney. A powerful stove, for example, can produce more combustion products than a narrow chimney can remove. Therefore, you must carefully perform chimney calculations.
  • Design Errors. The height of the smoke exhaust system is insufficient for its effective operation. The small length of the chimney can cause insufficient pressure differences. The optimum height of the chimney pipe is five to seven meters.
  • The narrowing of the smoke channels. Smoke paths have narrow and horizontally directed sections. In such places, soot accumulates especially actively, which interferes with the free movement of smoke.
  • Wind support. The chimney is located in the area of ​​"wind backwater". The cause of backwater can be, for example, a tall structure located next to the chimney.
  • Improper ventilation. Lack of ventilation or its illiterate device leads to a lack of the required volume of supply air. Therefore, it is important to pay special attention proper ventilation in a private house.

If the ridge of the roof is located above the level of the chimney, then the draft can overturn when a strong wind occurs.

Atmospheric indicators should also not be excluded from the list of reasons for the formation of reverse thrust. High humidity of the external air, as well as strong gusts of wind can cause the formation of reverse smoke movement.

The same phenomenon can be observed in the case when the air at home is colder than on the street. Due to the difference in pressure, a strong burning odor may occur.

To prevent poisoning, it should be well ventilated. At the same time, it will warm up at least a little. Wind is also capable of breaking traction, which forms turbulence of air flows on the roof. The wrong direction of the tip relative to the ridge of the roof contributes to this phenomenon.

Installation of heating in the bath
During the construction of the bath, it is necessary to arrange the furnace so that the chimney is indoors, because if you place it outside, condensation will form in the pipe

The installation location of the chimney also matters. For example, if we are talking about heating the bath, this part of the structure can be located in the inner part of the building.

Such a solution will allow to warm the room better, providing decent traction even in severe frosts. If the pipe is placed along the outer wall, heating will take longer, and condensation may form in the pipe itself.

Methods for checking chimney draft

The presence of backdraft can be detected even at an early stage of the problem before smoke begins to fill your home.

Let's start with folk ways. You can tear off a piece of toilet paper and bring it to the heater. Toilet paper is thin enough to respond well to air movement. Look in which direction the leaf deviates. If it oscillates towards the room, then there is a reverse thrust.

Traction check
You can check the craving in different folk ways, including using a candle: the direction of the flame of the candle will tell you the traction vector

Exactly the same experiment can be done with cigarette smoke. It looks even more clearly. Cigarette smoke will unmistakably show you the direction of traction.

The quality of the draft can be determined by observing the flame in the heating system. The white flame and the buzz in the chimney indicate too strong draft, which is also not good, since it leads to an excessive consumption of fuel. A good work result looks like this: the flame has a golden yellow color, burning occurs stably and evenly.

Wind meter
An anemometer (wind meter) is a popular device used by specialists who, by virtue of their profession, check the draft of a functioning chimney

For scientific verification, we need to arm ourselves with equipment. The most accessible instrument for ordinary users is an anemometer (wind meter).The appearance of the device, its variants are presented in the video, which is posted in the final part of this article.

Traction Problem Solutions

As it turned out, the reasons for the occurrence of reverse thrust can be different. Therefore, standard solutions do not exist. You need to look for an option that matches the problem in each individual case.

If the exit paths are blocked by debris or soot, then clean the pipe. If the paths are improperly designed, the structure will have to be completely dismantled and reassembled.

If the defect is the slow evacuation of the combustion products, there are several ways to improve the direct draft in the chimney. There are devices to help activate this process.

Option # 1 - deflector and its variants

In solving the problem, how to further increase the draft of the chimney, a deflector can help. It is mounted on top of the chimney. This device "draws in" smoke located in the chimney shaft, using wind power to achieve this.

Deflectors are a number of devices that have a single functional purpose: improving traction, preventing the reverse movement of fuel combustion products

The deflector has several functions at once:

  • protection of the mine channel from external clogging and precipitation;
  • increased draft in the chimney;
  • suppression of sparks arising from incomplete combustion of fuel.

The operation of this device is based on the laws of physics. When gas moves through a tapering pipe, its flow accelerates. In this case, the pressure that he exerts on the walls of the shaft decreases. There is a vacuum zone.

A deflector mounted on a chimney creates this rarefaction zone when air passes inside a tapering duct in its structure. Gases rush into the discharged zone located at the mouth of the chimney, and, with the help of traction, reinforced by the wind, are removed from the pipe.

Grigorovich deflector
The materials for the manufacture of the most popular deflectors are aluminum, stainless steel and galvanization, although there are also expensive copper products that resist corrosion well

Even the simplest deflectors can increase smoke removal efficiency by 20%. The presence of such a device creates huge advantages for the heating system, as it contributes to the complete combustion of fuel and better heat transfer. Therefore, it is deservedly popular and in demand.

Typically, the deflector includes two cylinders - the upper and lower, as well as a pipe connected to the lower cylinder, a protective cap and brackets designed to fix parts.

The upper cylinder is not a mandatory element of the device. A model without it consists of the following elements:

  • lower cylinder mounted on a smoke exhaust pipe;
  • diffuser - an element that cuts through the streams of air;
  • two caps - direct and reverse.

The most expensive deflectors are made of copper. In general, to create them, use ceramics and plastic, stainless steel, aluminum and galvanization. Aluminum and steel products are considered the most popular.

Despite the commonality of functions, deflectors are very different.They differ not only in their appearance, but also in the device, as well as their sensitivity to air flow.

Complex deflector
Difficult to manufacture, but very attractive spherical deflector looks very futuristic, although it is a wonderful functional device

The following deflector models are considered classic:

  • dish-shaped;
  • ventilation TsAGI;
  • Grigorovich's device;
  • H-shaped;
  • spherical "Volper".

In addition to all the recognized classics, there are relatively new models that are distinguished by unusual design solutions. This is a rotating model and a weather vane product. The basis of their work is all the same laws of physics, which were already mentioned above.

Don't want to splurge on a deflector? And it’s not necessary - it’s quite possible to make it with your own hands, using improvised materials. And how do we do it right reviewed here.

Option # 2 - Special Gate Valve

If there are problems with the stove, check the position of the gate. The gate is a shutter that is designed to regulate traction. They usually install it on the uninsulated first meter of the chimney pipe. This damper allows you to make the operation of heating equipment as efficient as possible.

This device has several functions:

  • after burning fuel with it, they block the pipe, which allows you to save heat for a long time;
  • as a draft regulator, the gate is used to change the cross section of the chimney: with excessive draft, for example, the smoke channel can be narrowed;
  • with his participation, it is possible to control the quality of fuel combustion.

The material for the manufacture of the gate is, as a rule, stainless steel, the thickness of which is 1 mm. Thanks to the polished surface of the product, soot is easily removed from it.

The temperature that such a valve can withstand does not exceed 900 ° C. It is quite durable and has a low coefficient of thermal expansion.

Retractable gate
The retractable shutter should not completely block the chimney door: 85% is the indicator that ensures safety standards when operating heating appliances

Shiber is presented by two models:

  • horizontal pull-out plate, which is most often used in brick chimneys;
  • rotary gate or throttle.

The throttle valve is called the same plate, which is fixed on a rotating axis, placed inside the chimney or pipe.

Rotary gate
The contours of the rotary gate plate repeat the cross section of the chimney, which allows it to almost completely block the pipe when the heater is not working

In view of the simplicity of the design make a choke for the pipe easy with your own hands. Such homework in operation will be no worse than the purchased product.

Option # 3 - chimney stabilizer

A product with such a speaking name is also called a breaker. This is a mechanism that automatically and metered supplies air to the chimney, allowing you to optimize the operation of the heating system without attracting a person to it. To prevent overpressure, the circuit breaker is equipped with a safety shutter.

Stainless steel is used to produce a chimney draft stabilizer. The maximum temperature that this device can withstand is 500 ° C.

Draft stabilizer in the stove chimney
The draft stabilizer installed on the chimney must be adjusted in accordance with the recommendations that you will find in the manual for your heating boiler

The essence of the stabilizer is that it automatically adds cold air directly to the chimney. In this case, the temperature and gas velocity inside the pipe are reduced. As a result, the efficiency of using combustible fuel is increased without any changes in the operating mode of the heater itself.

A breaker is installed, usually on the chimney pipe.At the same time, the distance from it to the heating device (boiler) should be at least 0.5 meters. The circuit breaker should only be indoors.

Since its functioning is based on a system of precisely balanced weights, the influence of natural factors on the operation of this device must be excluded.

The stabilizer setting can be considered complete when the minimum draft is set on its regulator in accordance with the data specified in the operating instructions for your boiler. Either the exact parameter should be set, or a division higher than recommended.

In addition to the use of these devices, to prevent back draft, you can extend the chimney pipe by straightening it as much as possible. Bends and sharp turns of the shaft increase cavitation during the removal of gases to the outside.

Conclusions and useful video on the topic

If the problem with draft is not manifested by puffs of smoke in all rooms, this does not mean that it does not exist. A device can help to identify it, the device of which can be found by watching this video here.

This product may save your life by paying attention to the problem in time, because carbon monoxide, for example, has neither color nor smell.

This video contains information about the appearance of the TsAGI deflector and its components. You can see how to build this device yourself.

If you feel the strength in yourself for the manufacture of a traction stabilizer, then this video will be for you a real guide to action.

Any device that operates in your home should work properly and not pose a threat to human life and health during its operation. Heating in this sense is no different from other useful devices. Deflector, gate and stabilizer will help to make its work stable and efficient..

You have a problem with draft in the chimney and are you trying to solve it on your own? Did you find the answers after reading our article? Or do you still have unresolved issues that we have missed? Feel free to ask them in the comments section, and we will try to clarify these points.

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Visitors Comments
  1. Garik

    In my cold weather, there is always a problem with the reverse draft of the chimney of the fireplace. In the summer, everything is fine, as it gets colder below +3 +5 again. What can be wrong?

    • Expert
      Alexey Dedyulin

      Hello, Garik. It would be nice if you attached a photo of how your chimney is arranged in the fireplace and an approximate diagram. And so, without seeing an example, you can give only general advice.

      Since the problem of backward thrust arises only in cold weather, when the temperature in the street drops below three degrees, it is necessary to insulate the chimney. As a heater, I recommend using Knauf Insulation Thermo-teK basalt cotton wool - the best option for the price / quality ratio.

      I also strongly advise you to mount a smoke vane on the chimney. This device is constantly located in the wind, preventing the cold wind from entering the chimney.

      Attached photos: