Backdraft in ventilation systems - causes and how to eliminate

Any apartment building has a ventilation system. She is responsible for the flow of fresh air into the room and the removal of stagnant air. But situations can occur when dirty air flows back into the house. This phenomenon is called reverse thrust. It interferes with the comfortable life of people, and also carries a potential danger. You can correct the situation with your own hands when there is no malfunction of the system itself. In other cases, you need to contact a special service.

Reverse thrust definition

With reverse draft, the flame is directed towards the room

Draft in the ventilation system is understood as a directed flow of air masses, which occurs when there is a difference in pressure in the house and on the street. The air flows naturally go to the low pressure area. By this principle, general house ventilation works. First, the air heats up, its density and mass decreases. It goes up and out into the vent. Fresh cold air comes in through the cracks and fills the entire space.

The thrust force is directly related to the height between the air inlet and outlet. For this reason, the residents of the upper floors feel the lack of fresh air more acutely.

The phenomenon of reverse draft in the ventilation of an apartment in an apartment building consists in the impossibility of removing dirty air. He goes back to the rooms and brings bacteria and unpleasant odors with him. You can understand that the system is not working correctly by the following signs:

• Fogging windows, condensation, mold and mildew. Excess moisture is also removed through the ventilation. If the system is not working properly, water will not be drained and will begin to settle.
• Stuffy stuffy air, often accompanied by an unpleasant odor.
• Draft from the air vent. If you bring your hand to it, you can feel what is blowing from the ventilation into the apartment.

The simplest test can be done using a regular sheet of paper. You need to attach it to the ventilation hole and see the direction of the oscillation.

Traction is broken - we make diagnostics

So, if you have a suspicion that you have a reverse draft of ventilation in the apartment, then it is worth making a diagnosis. For this, certain measures should be taken. For example, it is worth checking regulatory documents. They usually indicate exactly how the ventilation system in your home is performed. Having understood exactly how the ventilation system is arranged, you should figure out if everything is installed correctly. Sometimes the problem boils down to the banal - a mistake of workers during installation. After that, the correctness of the ventilation system is checked. If there are breakdowns, then everything is recorded and a plan is drawn up on how to fix everything.

Natural air circulation in the house

Backward thrust can occur when installing metal-plastic windows and doors

The ventilation system in the house is a complex of various technical devices, blowers and shafts, which have a single riser from the basement to the roof. Thanks to him, traction is created due to the temperature difference in the house and on the street. As this difference increases, the hood will work harder.

The effect is also exerted by the perpendicular pressure according to the principle of cross sections. This is a situation in which the wind blows horizontally in relation to the riser. As a result, it draws air out of the ventilation.

So that there is an air flow in the house and a vacuum does not form, vents are made in the foundation at the construction stage.It is also possible to make some holes in the floor on the first floor.

Thus, the natural circulation of air in an apartment building works. The system may not work if there is no supply ventilation or if the temperature in the house is lower than outside. The second reason does not occur often, therefore, it is precisely because of the lack of decent air flows that thrust appears. Ventilation shafts in the apartment are made in the bathroom, toilet and kitchen. Air enters through the windows. The use of double-glazed windows and sealed doors significantly reduces the inflow of air masses and causes reverse draft. To solve this problem, special valves are used for windows or walls.

Also, a violation of the air flow can be caused by a malfunction of the system, the installation of fans and hoods, and improper design. If the hood blows in the opposite direction in the apartment, you need to look for the problem and fix it.

Why is there a problem?

Normally, the system should take in dirty air from the inside and provide a full and timely inflow of clean air, but sometimes various violations may occur. If ventilation works in the opposite direction, what to do in this case? First, you need to understand the possible causes of this phenomenon:

• Perhaps the problem lies in improper installation, if the pipe, which should go outside, was placed incorrectly, relative to wind flows. In this case, the wind can simply begin to blow into this pipe, and cold air will fly into the apartment.
• It may happen that a kind of blockage from cold air and steam occurs in the ventilation ducts, as a result of which, these mixed substances will interfere with normal ventilation.
• Mechanical obstacles can also form, which are very different, ranging from dirt and soot, which could have formed with prolonged use and lack of cleaning, and ending with bird's nests, if some birds suddenly decided to settle in the pipe.
• If the room is large and at the same time there are no partitions in it, then its own air flows are formed there, in other words, drafts. Their presence can interfere with the normal operation of the ventilation system.
• Various artificial objects and sources of air currents also interfere with work. This can apply to both fans and heaters, as well as a conventional hood in the kitchen. Modern devices are quite powerful, so the standard system can no longer cope with such air flows.

  

• Problems with draft in a private house may be associated with a chimney that leads to the roof from a stove or fireplace. You need to inspect this pipe and check its condition to make sure everything is in order with it.
• Sometimes it may turn out that plastic windows are the culprit for violations, especially if they were installed in an old house, replacing wooden ones. The fact is that these structures are completely sealed and do not allow air to pass through. And the ventilation system was designed taking into account the old, wooden windows, so as a result, the air flows are wrong. In this case, installing special air outflow valves on new windows can help. This operation can be performed by companies that are engaged in the installation of plastic structures.

Sometimes the reason for the malfunctioning of the ventilation system in an apartment building can be an incorrectly carried out redevelopment at the neighbors. Therefore, if no apparent reason is found in your apartment, it may be worth asking if the neighbors have recently carried out repairs that could affect the state of ventilation.

Reverse thrust reasons

If the ventilation duct is clogged, reverse draft occurs or ventilation does not work

The main reason for the occurrence of reverse thrust is the violation of the principle of natural air exchange. It is caused by the following factors:

• The use of plastic windows and sealed doors. They are able to completely block the access of fresh air to the room.
• Alteration of the ventilation duct or illegal demolition.
• Incorrect pipe design or incorrect location. If it is installed in the wind shade zone, circulation will be disrupted.
• Change in wind direction.
• Clogging of the ventilation duct with small debris, birds entering it.
• Constructive errors.

To identify and eliminate reverse thrust, you should contact a specialist. It is better to choose independent experts who will conduct a comprehensive analysis of the entire air duct system in the building and give recommendations on how to improve the situation.

General house reasons for the appearance of external traction and the fight against them

Signs of the influence of such factors are considered to be the appearance of reverse thrust or a significant deterioration in normal in several apartments of a multi-storey building, the ventilation of which is tied to the same channels. Most often, problems are associated with the following reasons:

• The ventilation duct needs cleaning. During operation, impurities entering the room air, from soot to fat, settle on its walls. As a result of a decrease in the cross-section, the ventilation duct is not able to pass the entire flow, a backwater is created, and part of the air is removed along the path of least resistance - to the apartment of the upper neighbor, and not outside the roof.
• A common reason is the effect of the wind on an incorrectly designed head of the ventilation duct when exiting the roof. Blowing into the channel, wind currents create eddies in the upper part, which increase the aerodynamic drag of the network. As a result, the air again follows the path of least resistance, causing back draft. The reason lies in the insufficient height of the headboard or its incorrect location on the roof. The problem is solved by building up a pipe or installing a deflector.
• The reason is related to the increasing popularity of renovation of apartments with redevelopment. As a result of such excitement, ventilation niches and ducts in which channels are laid often suffer. When these structures are destroyed, all air ducts are simply muffled and sealed. As a result, in the presence of traction, all the air that was previously diverted to the roof will flow to the apartment closest to the place of destruction, that is, to the neighbor below.
• The connection of powerful hoods to general ventilation networks by residents from apartments, which are also located on the lower floors, leads to a similar effect. Old ventilation ducts are not designed for such a flow rate of air, which becomes the penetration of its part into the apartments of neighbors. It is possible to solve all problems with reverse draft caused by the actions of other residents only after eliminating the reasons - to restore the ventilation duct, remove a powerful hood. In extreme cases, installation of a grill with a check valve at the outlet of the ventilation duct will help a little.

It is important to remember that self-cleaning of common house ventilation ducts is not allowed, this problem is solved only through the management company.

In some cases, reverse thrust is associated with global problems. If the design is incorrect, there may be a redistribution of flows in the apartment hood due to the access staircase, elevator shaft or garbage chute, smoke removal system. But it will not be possible to eliminate such problems on your own, this is a rather complex technical task that requires serious calculations.

System check

An air sample is taken to check ventilation

A check is carried out to identify faults and eliminate faults. It consists of the following steps:

• Study of design documentation. Checking its compliance with the norms and standards of GOST.
• Evaluation of the effectiveness of the installed equipment, the correctness of its installation and operation.
• Checking the quality of the installation work of the duct, ducts and other elements of house ventilation.
• Air sampling.
• Search for unauthorized channel overlap.

On the basis of the test carried out, the specialists decide how to eliminate the reverse thrust.

Elimination methods

Supply valve on a metal-plastic window

To remove the backdraft, the ventilation system must be brought into operable condition. The main ways to restore work that you can do yourself include:

• Check valve installation. The device will not allow old air to return to the room again.
• Installation of supply valves on windows. Thanks to this mechanism, fresh air will flow into the house, even if the window is closed. The intensity can be adjusted. Also, the valves can be equipped with fans, debris grates and other attachments for cleaning, heating and cooling air masses.
• When installing a powerful hood, it is necessary to balance it in terms of performance. The volume of the incoming air must be equal to the displaced one.

If the weather conditions are the cause of the draft, you need to wait until the temperature and humidity, as well as the wind direction, return to normal. Such factors are temporary and do not depend on the person. With frequent influences of weather conditions, you need to think about redeveloping the system.

The ventilation must be cleaned every 5 years.

If damage has occurred due to which the hood blows in the opposite direction in a private house, you need to call the repair service. Experts carry out the following activities:

• Protect the mouth of the mine if draft is generated by strong gusts of wind.
• Restore damaged structures, make their repair or replacement.
• The channels are cleaned. It must be carried out at regular intervals. Do not clean the ventilation yourself.

It is not always possible to correct the factors affecting traction. For example, the features of the layout of the room may be such that stagnant air will return to the room. In large rooms without walls and partitions, drafts will appear, which affect the overall ventilation system in the house. Stagnant air masses can also return from the stairs to the second floor.

If the reason was the wrong design of the ventilation duct, you should rework it.

How to troubleshoot problems

Depending on why it is blowing from the ventilation into the apartment, the corresponding methods of solving the problem found are also applied. Different actions are provided for each case:

• Sometimes, in order to restore the normal operation of ventilation, you just need to open all available windows and fully ventilate the room. In some cases, the problem is caused by a sudden change in atmospheric pressure or a change in wind direction, so it can be easily solved. Airing is the first action that should be taken if any problems have been noticed. If this does not help, then you will have to further figure out why there is a reverse draft in ventilation, and use the help of specialists.
• If any irregularities were found directly in the operation of the ventilation system itself, then a special device can be used to eliminate the problems - a deflector, which changes the direction of the incoming air flows and normalizes the operation of the system.
• From time to time, it is necessary to clean the channels, since various debris, dirt and soot accumulate inside, and birds may also settle there, deciding to make a nest. If the problem is due to the fact that the channels are clogged with dirt, then you will need to call a special service that will clean and remove the blockage.
• In the event that the problem lies in the presence of drafts walking in the room, redevelopment will help, which will create the necessary obstacles in the path of air flows.Additional doors can be installed to eliminate drafts.
• It is worth considering that the staircase is an important part in the process of forming the existing air flows, so its installation must be carried out in accordance with building codes so that it does not cause problems. In fact, it is a huge pipe and has a similar effect on the ventilation system. A curved design has less impact on ventilation than a straight design.

Some ventilation problems can be solved on their own, but to eliminate more serious defects, a call of specialists will be required. Before contacting them, it is recommended, if possible, to conduct an independent check, having tried simple methods, for example, airing the room. We must not forget about the timely cleaning of the ventilation so that it does not cause problems.

Preventive measures

Installing a deflector helps to avoid blowing wind into the channel

Troubleshooting a backdraft problem can take a lot of effort, time and money. To avoid this, you need to take preventive measures. Basic tips:

• The system must be in good working order.
• Fans and hoods should not be placed in ventilation ducts. It is possible to use only recirculating hoods or to discharge them outside through a wall or window.
• Deflectors and rotary turbines are placed at the end of the riser.
• Organization of the inflow of fresh air from the street in any available way, including in winter.
• Installation of interior doors to block the possibility of a draft that affects back draft.
• Cleaning the system from ice and snow in the winter.
• Periodic ventilation check.

These measures will help to avoid most of the problems due to which reverse draft is formed and cold air blows into the apartment from the ventilation.

Ventilation system functions

Ventilation at home is essential to maintain a healthy and pleasant indoor environment. The system performs several functions:

1. Outflow of unpleasant odors from the house.
2. Fresh oxygen supply.
3. Purification and humidification of incoming air.
4. Protection of wall structures from excessive moisture.

Thus, passing through the ventilation system, the air enters the room already clean and humidified, and the exhaust polluted air is discharged in parallel. This structural element must be foreseen during the construction phase. Without a ventilation system, no room can function normally, especially in apartment buildings and office buildings, when there are many people in a small area. The functionality of ventilation is extensive, so only high quality materials must be used for its construction.

Where to go

The ventilation of the apartment building is shared. If there are problems, reverse thrust will appear in all apartments, so you need to act together. First of all, you need to discuss the problem with all the residents of the entrance. Perhaps a very powerful hood is installed in one apartment, which damages the operation of the entire system.

Next, you should contact the management company with a request to find and solve the problem. In the event of the appearance of cold musty air, you can contact the gas company. This decision is due to the fact that ventilation is a security system. It is the presence of reverse thrust that does not make it possible to ventilate the room from energy carriers and products of its combustion.

If reverse thrust appears in the house with a certain frequency, and it cannot be eliminated, part of the windows should be replaced with anti-explosive ones.