Exhaust fan blowing backwards


And now it will be easier to understand what may be the symptoms and causes of the kitchen hood not working properly and how to deal with it.


If you can hear noises and smells in the kitchen even though the hood is on, it does not mean that it is not drawing in air. The problem may be due to improper operation. For example, the cooker hood must be switched on a little before cooking begins and off a few minutes afterwards. This approach is the most effective way to prevent the buildup of odors in the room.

Another reason for this symptom is the low efficiency of the filter. It should be replaced or cleaned (if provided by the manufacturer). It is also recommended to clean the grid: it may accumulate fat, which prevents the proper air flow.

In some cases the contact between the fan and the motor is broken. So there is no power to the device, so the fan does not rotate. In this case it is necessary to call the contacts, to eliminate the cause.

It does not turn on

  • The appliance may not be plugged in. Check that there is voltage in the mains and that the plug is properly inserted into the socket. As simple as it may sound, but such causes of the device not working are quite possible. And even common.
  • Button doesn’t work. You can use a tester to determine if it is working. A piercing test will help to determine the cause. If it does, you must either replace the button with a new one or repair it.
  • A wire or plug is damaged. These items need to be checked. If necessary, replace it.
  • The fuse has blown. If so, it will have to be replaced.
  • Disconnection of the electric circuit inside the unit. You must use a tester to check everything. If there are bad contacts, they need to be cleaned and treated.
  • The motor is out of order. If this happens, the unit is unlikely to be repaired, much less by yourself. Therefore, as a rule, it has to be replaced. However, very often such a procedure is not economically viable. And then it’s more effective to replace the entire hood.
  • Engine control unit does not work. As a result can not switch speeds. The reason can be a defect in the starting capacitor. To check the functionality of a multimeter is used.

Back draft in the apartment, what to do?

In order for the ventilation to work properly the air must be coming from the street. Optimal solution, in our opinion to install a valve KIV-125, sometimes it is called an alpine window. It is a plastic round cap on which the airflow regulator is located. Installed such a device near the window, for this purpose in the wall drilled a through hole to the street diameter of 13 cm, outside installed lattice, inside the drilled channel mounted insulation. Modern construction equipment allows you to do this work in just 2 hours, without dust and dirt!

  • No draughts
  • No noise from the street
  • The filter prevents the entry of gnats, mosquitoes and other insects.
  • Through the valve will constantly enter fresh air from the street in small quantities.

To see more about it click on this link: http://brizer-m.You will not be able to fix the back draft through one KIV-125 valve

Air inlet valve KIV-125 1900r

Such a valve is needed in each habitable room. In many cases, installing the FIB saves you from reverse draught. In a two or three room apartment 2 or 3 bell flaps, respectively, provide the necessary air supply. But it happens that in a one-room apartment is such a situation:

Capacity of one KIV-125 is not enough to completely eliminate the back draft. It is enough to: reduce the humidity in the room, get rid of condensation on the windows, mold. Of course, all situations are individual, for some it is enough 1 valve.

How ventilation works in the apartment?

The problem when the ventilation blows into the apartment, most often occurs due to the lack of special devices in the duct system, allowing to make this process forced. That is why it is referred to the usual supply and exhaust system. The principle of its functioning:

Getting air into the house occurs through various openings and slots, and this creates a natural draught, which removes the dirty air in the ventilation shaft. Restoration of the air duct of this type is not possible without the presence of fresh air from the street. In Soviet buildings, such an inflow was provided, the same tandem “wall window” was loose, which provided the necessary inflow of air. But now energy saving is promoted and encouraged at the state level, so everything is aimed at maximum tightness of connections. These are windows and doors with seals, not necessarily of plastic, modern constructions and made of wood make also maximum tightness.

Important! All energy saving constructions do not let the air in the apartment, so you need to think how to improve ventilation, because in this state it will not work.

What is draught and reverse draught

Draught is a directional air flow that occurs due to pressure differences inside and outside the room. Air currents tend to move from a high pressure area to a low pressure area. The general ventilation in an apartment building works on a similar natural supply and exhaust principle:

  • The air in the room heats up, becomes lighter (density decreases).
  • Warm air rises in an upward direction pushing it into the ventilation.
  • Cold air comes in through gaps and holes in the room.

The air inside the room has a higher temperature. According to the laws of physics, it rushes upwards. The greater the temperature differences between the outside and inside of the dwelling and the greater the height difference between the inlet and outlet of the air masses from the apartment, the greater the draught. Therefore, as a rule, people living on higher floors feel the lack of fresh air more acutely. The reverse draft in ventilation occurs when the exhaust air does not flow outdoors but back into the room.

How the extractor works

A normal house ventilation system functions on the principle of air replacement. It is created by the inflow of air through the windows, which displaces with its mass of the exhaust carbon dioxide gases and unpleasant smells. Air exchange takes place through bathroom, toilet and kitchen air vents.

The duct system then conveys the flow to the roof of the house through an exhaust stack equipped with a protective baffle. The latter has two functions:

These requirements for the device exhaust system are covered in the approved standards (GOSTs). But in fact not everything is as it is written on paper. During operation, there are a number of factors that negatively affect the building ventilation system, which subsequently causes back draft in the pipe.

Causes of back draft in ventilation

Reverse draught occurs due to the presence of miscalculations in the design of the ventilation system or not qualified execution. But since air has well studied physical properties, the causes of the problem can easily be identified and remedies can be found.

The law of conservation of volume in ventilation

When modeling air exchange for small volumes by the law of conservation, which is typical for private houses, it is possible to neglect such parameters of the air medium as degree of compression and uneven density.

In this case, the basic physical law of the supply and exhaust ventilation can be formulated as follows: the difference between the volume of incoming and outgoing air in any period of time is equal to zero.

Exhaust ventilation is installed in places where the greatest accumulation of contaminating aerosols. These are the bathroom, kitchen and service rooms. Some exhaust hoods are equipped with fans for forced augmentation of the extracted air volume.

Fresh air supply ventilation is installed in living rooms to bring fresh air into places where people stay all the time. Typically, it is of the forced-air type with a predetermined volume flow rate.

This is necessary to maintain accurate microclimate parameters such as temperature, humidity and oxygen conditions.

Most of the time, the air intake volumes are fixed at different places in the house and the exhaust air flow distribution is variable.

If at some point in time, part of the exhaust system let in more air than the supply air, the lacking volume is compensated for through the holes designed for air discharge.

To prevent this scenario, the following set of measures must be taken when designing the ventilation system:

Exhaust fan reverse connection|एग्जास्ट फैन का उल्टा कनेक्शन कैसे करते हैं by Electric Guruji

  • Install a non-return valve on each exhaust outlet to prevent airflow through it;
  • Arrange one or more redundant natural air inlets to compensate for the missing volume.

Openings of the reserve air inlets should be sized so that they would be able to compensate for the maximum total lack of air. Each of them must be equipped with a non-return valve to prevent air outflow. This is fraught with icing and clogging of air inlets in winter.

Unaccounted for air exchange from the outside

Filtration contributes to the house air balance by allowing uncontrolled air flow through gaps and imperfections, i.e., so-called unaccounted air exchange with the outside. If this phenomenon is intensive, it is impossible to make accurate calculations on the parameters of the ventilation system.

In addition, infiltration (filtration directed inward) allows air to enter the room without treatment with dust filters and without heating to a suitable temperature in winter. Therefore, this phenomenon should be completely eliminated or its impact on the overall air turnover should be made negligible.

Open windows, balconies and skylights provide additional airflow. It is impossible to calculate it reliably in advance since the speed and even the flow vector depend on many factors, especially external and internal temperature, and also the direction and intensity of the wind.

The only solution to the detection of back draft in the ducts can be the installation of non-return dampers.

During the cold season a chimney serves as an additional extractor with variable power. The hot air with combustion products escapes through it, making a significant contribution to the total value of the exhaust flow.

The volume of air escaping through the chimney depends on the capacity of the boiler. For factory-made products, it is easy to calculate, since the manuals have tables that show the minimum cross-section of the chimney and the rate of exhaust of combustion products for a particular model.

If the furnace or boiler is self-made, the approximate value of the volume of air exhausted should be taken from the technical documentation of a similar parameter device.

If we consider the chimney as an exhaust duct, its peculiarity is the impossibility to install a check valve on it. An integrated chimney pump can be an alternative, but only if its installation is technically possible. Then the heating can be included in the model as an exhaust with a fan.

To calculate the air balance in the presence of the chimney must be approached responsibly. Even a single reversal of the flow can completely spoil the interior of the room. There is also a risk of fire and the possibility of poisoning by combustion products if there are large flames.

Where to go with problems with the ventilation system

If a person has no idea about the circulation of air flows, then at detection of back draft in the ventilation of the apartment in an apartment building, he does not know what to do. The best way out in this situation is to contact the management company. An application needs to be written and an inspector will be sent for inspection. He will assess the condition of the ventilation system and take further corrective action.

If the management company does not respond to the tenant’s request or issues a refusal, you must complain to higher authorities (housing inspection and Rospotrebnadzor). The staff of these authorities will make a further decision about repairing the ventilation system and cleaning it.

Determining the back draft

The draft in the ventilation system is understood as a directed flow of air masses that occurs when there is a pressure difference between the house and the outdoors. The air flows naturally into a low-pressure zone. This is the principle on which the apartment ventilation works. The air first heats up, reducing its density and mass. It is routed upwards and led out into the ventilation opening. Cold, fresh air comes in through the cracks and fills the whole space.

The strength of the draught depends on the height of the air inlet and outlet. That is why people living on the lower floors feel the lack of fresh air more acutely.


The phenomenon of reverse draught in the ventilation of an apartment building is the inability to exhaust dirty air. It comes back into the room and brings with it bacteria and unpleasant odors. You can tell if the system is not working properly by looking at the following signs:

  • Misting of the windows, condensation, mould and fungi. Excess moisture is also expelled through the ventilation. If the system does not work properly, water will not drain away and will begin to settle.
  • Stuffy stinky air often accompanied by an unpleasant odor.
  • Draft from the vent. If you bring your hand to it, you can feel that it blows from the ventilation in the apartment.

The simplest test can be done with a piece of paper. You need to put it against the vent and see the direction of oscillation.

Why the ventilation in the apartment works in the opposite direction

Causes of improper functioning of the ventilation system:

  • Tightness of the room. Normal air circulation can be impaired by not allowing air into the apartment from other sources. The reason for this are modern plastic windows, which, unlike wooden options, do not let air flows through.

Hot air rises up the pipe and cold air occupies the vacated space. A pressurised room can create low pressure, which causes a back draft effect. Good draft in the pipe will only cause a delayed effect. To correct the situation, you will need to install additional ventilation and intake valves.

  • Duct cross sectional calculations are incorrect. The ventilation system functions at a higher intensity when compared to the chimney. Rapid heating leads to faster movement of air through the chimney.
  • The chimney is located in the “wind shadow”. The reverse draft effect appears when the chimney is located in a place where air movement is obstructed by building construction.
  • Stairs are designed incorrectly. A staircase is essentially a large pipe, which can be the cause of improper air direction. Spiral and curved types of stairs can reduce the impact on ventilation performance.

Checking methods

Unpleasant smells, drafts, mold and mildew appear if there are problems with ventilation. In order to be sure of the cause of the problems, you need to know how to check the system. To do this, open the vent in any room, and then a sheet of paper should be attached to each ventilation grille.

The ventilation works properly if the paper is attracted to the grille. If the leaf does not move, the system is not functioning. The work of the ventilation is disturbed, if the paper is flying off the grille, which is due to the reverse draught. In this case, all dirt and odors do not escape from the apartment, but enter it from the hole.

Ways to fix the problem

What to do to eliminate the back draft:

  • Cleaning the aisle. This will require removing the vent grille and removing accumulated debris with a broom or vacuum cleaner. If construction debris has gotten into the sump, the cleaning procedure can only be performed by professionals.
  • Install plastic windows with valves or install them additionally. can be equipped with special fans or deflectors installed on the extractor fan in the toilet

Using any of the methods to fix the problem will require consultation with a specialist. The biggest work must be done if the reason the system is not working is an error in the layout or construction of the system.

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