Plastic hood boxes: overview of views + installation rules

Forced ventilation systems are present in almost every apartment or private house. They consist of an air intake device and exhaust hood, which can be made of various materials.

The plastic version is widely used because of its low cost, durability and ease of installation, which can be carried out independently.

The main parameters of existing systems

For the normal functioning of the ventilation system using exhaust hood, it is necessary to correctly calculate the parameters of the duct. In most cases, for domestic purposes, you can pick up plastic boxes of typical shapes and sizes.

Rules for the selection of the duct section

The main parameter of the ventilation duct is its internal section. From him and from the power of the hood depends on the speed of flow through the channel. The cross section is chosen based on the maximum amount of air flow.

There are no regulatory documents regulating the speed for domestic plastic air ducts, therefore they are guided by the values ​​verified by practical means equal to 3-7 meters per second.

The size of the box section is taken to be equal to or slightly larger than that of the exhaust duct branch pipe, the size of which is indicated in the passport of the device.

If regular activation of the maximum mode is not planned, then in this case a proportional reduction in the cross section of the ventilation duct relative to the size of the outlet opening is permissible.

Multi-power hood
For small kitchens, you can not use the maximum power hood. This allows using an adapter to use a duct of a smaller diameter than specified in the instructions.

So ifS- the cross-sectional area of ​​the exhaust duct,N- the volume of air flow at the maximum mode of the device,M- the volume of air flow in the planned mode, then the required cross-sectional area of ​​the box is calculated by the formula:

P = S * (M / N)

The insufficient size of the cross section of the duct leads to significant air velocities, an increase in the friction force and, as a result, the following negative effects:

  • there is an increase in the load on the ventilation mechanisms of the hood, which leads to a decrease in the operating life of the device and the additional cost of electricity;
  • due to an increase in resistance, a decrease in maximum performance occurs, which reduces the air circulation in the room;
  • as a result of the occurrence of aerodynamic effects in the ventilation duct, the noise level during operation increases;
  • there is an increase in air pressure from inside to the elements of the system, as well as the occurrence of vibrations, which requires a more reliable fastening and sealing.

If the cross section of the box is larger than necessary, this will not adversely affect the functioning of the forced ventilation system, but will lead to unnecessary financial costs.

In addition, ventilation ducts and other large components are more difficult to install and integrate into room designs.

Airflow rate calculation table
The calculation table for the dependence of the flow rate on the extraction power and the diameter of the round duct allows you to correctly select the size of the ventilation channel

Types of forms and sample sizes

Plastic boxes for ventilation are round or rectangular in shape.The circumference has the smallest perimeter compared to other geometric shapes with the same area.

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Plastic duct in the kitchen
Plastic duct in the kitchen
Square ventilation duct
Square ventilation duct
Rectangular plastic duct type
Rectangular plastic duct type
Exhaust system of round tubes
Exhaust system of round tubes
Combination of elements with different section
Combination of elements with different section
Combined channel from round and rectangular sections
Combined channel from round and rectangular sections
Fastening the plastic components of the box
Fastening the plastic components of the box
Compatible channel with trim and materials
Compatible channel with trim and materials

Therefore, from the point of minimizing the resistance of the inner surface of the duct to the movement of the air flow generated by the hood, it is preferable to have a round channel shape.

On sale for domestic purposes the most common round plastic boxes of the following diameters:

  • 80 mm, sectional area of ​​50.3 square meters. cm;
  • 100 mm, sectional area 78.5 square meters. cm;
  • 125 mm, sectional area 122.7 square meters. cm;
  • 150 mm, sectional area of ​​176.7 square. cm.

Rectangular ventilation channels are easier to fit into the interior of the room, as well as placed in the niches above the kitchen cabinets, above the suspended or suspended ceiling.

The most common boxes of the following sizes:

  • 110 x 55 mm, sectional area 60.5 square meters. cm;
  • 120 x 60 mm, sectional area 72 square meters. cm;
  • 204 x 60 mm, sectional area of ​​122.4 square meters. cm.

If necessary, you can find elements of a larger ventilation system. These are plastic boxes for domestic purposes of a round shape with a diameter of 200 mm and a rectangular size of 220x90 mm.

However, before making a choice in favor of non-standard sizes, you must make sure that you can purchase all the elements that allow you to build an air duct for drawing the desired geometry.

Multi-colored plastic pipes for ventilation
The extensive color range of plastic pipes and boxes for ventilation of residential buildings makes it easy to fit the duct into the interior of the room

Plastic shaped elements

Ventilation systems from exhaust to mine have different geometries and topologies due to individual approaches to kitchen planning. Therefore, special elements are provided for the implementation of virtually any configuration of a plastic box.

Ventilation ducts are straight elements of a rectangular or circular duct. Their standard length is 0.35; 0.5; 1; 1.5 and 2 meters, however, you can independently saw off a piece of the required size using a hacksaw or grinder.

If you want to get a straight section with a length of more than two meters, then it is mounted using several standard length fragments using special connectors for plastic channels.

In this case, the increase in the length of the section due to the size of the connector does not occur.

Another necessary element is the knee, with which the duct is rotated through an angle of 90 or 45 degrees. For rectangular boxes, elements are distinguished for changing direction horizontally and vertically.

To rotate at angles not multiples of 45 degrees, use the so-called multi-angle knee. Depending on the angle required, one of the sides of the connector is cut off.

Shaped plastic elements set 1
Shaped elements: 1 - rectangular bore; 2 - round channel; 3 - round channel connector; 4 - vertical knee; 5 - horizontal knee; 6 - multi-angle knee

To change the shape of the box from round to rectangular (or vice versa) use special adapters.

Their use, as a rule, is due to the difference in the shape of the ventilation ducts with an exhaust funnel or a hole in the grille. They can be both direct and angular shapes.

The following variants of the transition are most common:

  • from a diameter of 100 mm to a size of 110x55 mm;
  • from a diameter of 100 mm to a size of 120x60 mm;
  • from a diameter of 125 mm to a size of 204x60 mm.

If you need to make the transition to a different size of the plastic box without changing its shape, then use gearboxes. For round options there is a special universal adapter that can be used to connect all standard sizes.

For structures with a complex topology, tees are provided, with the help of which air flows from several extracts, for example from the kitchen and from the bathroom, can be made towards the exit.

They can be rectangular, round, and also the combined form.

Shaped plastic elements set 2
Shaped elements: 1 - flat channel connector; 2 - round knee; 3 - straight adapter; 4 - corner adapter; 5 - round gear; 6 - rectangular gearbox

Fastening elements of the box to the wall occurs with the use of holders. Since plastic structures differ from metal ones by low weight, their installation is not a difficult task.

These factory-made parts are inexpensive and fit well into the interior of the room, so the use of self-made structures is impractical.

A wall plate or grille is fixed over the hole in the wall leading to the ventilation shaft or to the street. The grille, if necessary, may contain additional slots for natural ventilation.

In this case, it is necessary to provide protection against penetration through these openings of the air flow generated by the hood back into the room.

To prevent the occurrence of return thrust when the exhaust hood is not working, a check valve is used. It can be integrated into the plastic duct connector, or the ventilation grille can perform its function.

In the absence of such a device, air from the street or from the ventilation shaft may enter the room.

Shaped plastic elements set 3
Shaped elements: 1 - universal round gearbox; 2 - round tee; 3 - tee rectangular; 4 - round holder; 5 - rectangular holder; 6 - overlay for round channels

Design and installation features

Installation of a plastic box for ventilation from the kitchen hood can be done independently without the involvement of specialists. It is necessary to take into account some simple features of the design and installation of such systems.

The installation of a plastic system includes a number of traditional steps that must be passed both by an independent master, who has decided to build a box with his own hands, and by a hired worker.

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Assembly of duct parts on the floor
Assembly of duct parts on the floor
Input to the fan room with non-return valve
Input to the fan room with non-return valve
Validate input setting
Validate input setting
Assembling a plastic channel on the floor
Assembling a plastic channel on the floor
Connecting the box to the knee of the hood
Connecting the box to the knee of the hood
Consistent connection of elements
Consistent connection of elements
Testing ventilation work
Testing ventilation work
Ready to use plastic box
Ready to use plastic box

Stage # 1 - selection of the geometry of the ventilation system

A large variety of structural elements allows you to implement almost any geometry of the plastic ventilation duct.

However, to maintain the functionality of the air passage system at the proper level, the following rules must be observed when designing an air duct:

  1. Box length. If possible, minimize the length of the box. The optimal distance from the exhaust pipe to the ventilation grille is considered a distance of less than 3 meters.
  2. Fewer items. It is advisable not to use a large number of elements that change the direction of air movement. Bends, contractions and various transitions create additional aerodynamic drag.
  3. Minimum of turns. It is necessary to minimize the number of knees with a rotation of the box by 90 degrees. They create the greatest resistance to flow movement, generate noise and accumulate sediment in the form of fat and dust adhering to it.

In the case of placing the box near the heating tower or other heat source, it is necessary to prevent the plastic from heating to temperatures above 50 degrees Celsius.

To do this, you need to either bypass the hot object or lay the insulation between it and the air duct.

It is easiest to use polystyrene as an insulating material, since it has a low thermal conductivity and will not create noise when the box vibrates.

Bypass heating stand with the help of the knees
The implementation of the bypass of the riser heating using four knees with a 90 degree angle. With a different orientation of the channel, if the narrow part were turned to the wall, it would be possible to manage with angles of 15–20 degrees with the help of a multi-angle knee

Stage # 2 - Installation of a check valve and grating

A necessary element of the ventilation system is a check valve, whose role is difficult to overestimate.

If the box goes only from the exhaust hood to the mine and has no branches to other sources of air intake, then the valve is installed at the end of the duct or use a special grille with “blinds” that prevent the return of air.

If there are several sources of air intake into the ventilation system, a check valve is installed near the connection of each branch to the main duct and another one near the grille.

Layout of check valves
Typical solution for placing check valves in a ventilation system with two air intake points and an external grille

If it is necessary to support natural ventilation with the hood turned off, there are three solutions:

  • to separate the outlets for forced and natural ventilation, and they should not go into the same ventilation shaft;
  • near the outlet, install a tee “exhaust - grill - check valve”;
  • use a ventilation grille with slots for the natural movement of air and protection against reverse thrust.

Birds or rodents living in the ventilation shaft sometimes get inside the duct. Caught in the bends of a plastic box, they can die, resulting in decomposition products into the room.

To prevent such a development of events, the grid leading to the street or the mine is often provided with special protection that is insurmountable for animals.

Protection against the penetration of animals into the duct
Protection of the ventilation grill against the penetration of birds and rodents significantly narrows the cross section, which must be considered when calculating the diameter of the hole

Stage # 3 - fasteners and duct placement

The sections of the plastic duct from the exhaust hood to the ventilation grille can be fixed in different ways depending on their position relative to the cabinets, walls and ceiling.

In any case, the installation is not difficult and can be done independently.

However, it is necessary to approach this procedure responsibly, in order to avoid the occurrence of noise from vibrations, as well as sagging or other deformations of the box with possible subsequent depressurization.

If the box is located inside the cabinets, then it is fixed to the back wall of the cabinet using clamps. Also fix the place of passage of the duct through the walls with foam or polystyrene inserts.

These materials do not emit noise when they come into contact with the vibrating elements of the system.

If a part of the duct is located above the cabinets, the easiest way is to fix it to the cabinets with the help of holders and screws on a small length of wood.A plastic box in this position does not create any significant lateral pressure.

When attaching the duct to a wall or ceiling, holders are recommended to be positioned after 1 meter. Fixation takes place with the help of special clamps, which can be purchased under the shape and size of the purchased box.

The weight of the entire plastic construction is small, so its mounting is quite simple.

Installation of a hidden plastic box
The plastic box can be completely hidden behind a false ceiling and plasterboard. In this case, it is permissible to carry out sealing and fastening of the entire structure without taking into account its visual perception.

If the plastic box is covered with a stretched or suspended ceiling, then it is necessary to check the reliability of its fixation when the extractor is operating at maximum power. In other cases, the mount can easily be strengthened after finding weak spots.

Sometimes during operation of the ventilation system, rattling or knocking may occur, caused by the contact of the vibrating elements of the plastic box with solid objects, such as a cupboard, a wall, etc.

In this case, instead of additional fastening, it is enough to lay foam rubber or foam between them.

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Air duct from sewer pipes
Air duct from sewer pipes
Suspension of polymer duct
Suspension of polymer duct
Conclusion homemade ventilation on the street
Conclusion homemade ventilation on the street
Sealant use in joints
Sealant use in joints

Stage # 4 - ensuring the tightness of the structure

Elements in a ventilation system made of plastic parts do not have a gasket. The dimensions of the joints are well adjusted, but after some time due to deformation, the density of some compounds may decrease.

In the event of a leak in the joints of the structural elements, air from the ventilation system may penetrate to the outside. In this case, odors and moist air spread through the rooms through which the duct passes.

In addition, with the passage of air through the cracks sometimes there is considerable noise.

Tight connection of plastic box elements
Despite the fact that all elements of a high-quality plastic box fit snugly together, it is better to spend some time sealing the joints.

To prevent depressurization of plastic ventilation ducts, there are two solutions:

  1. Sealant. Grease the joints with special silicone or acrylic sealant.It is applied in a thin layer on the edge of the element before it is inserted into the system.
  2. Scotch. To wrap joints with self-adhesive tape. This method can be applied after installation of the system in case of detection of places of depressurization.

The first method is more reliable, however, serious problems may arise if you need to parse the ventilation duct for repairing, cleaning or changing its geometry.

Over time, the sealant fastens the structural elements so strongly that in some cases you have to sacrifice one of the parts to start the system.

The external sealing method, on the contrary, makes it easy to disassemble a plastic box. However, this method affects the appearance of the structure, so it is practically not used if it is located in plain sight.

Conclusions and useful video on the topic

Installation of the kitchen box. Elimination of gaps in the joints of structural elements using silicone sealant and screws.

Vibration prevention by using foam in the following video:

Installing a plastic duct for exhaust in the kitchen.Fastening elements together, fixing to the ceiling with the help of holders:

The work of the check valve for the functioning of natural ventilation on the example of the tee "hood - grill - natural ventilation":

The information we presented about the selection, methods of construction and the main components of plastic ventilation ducts will help you to build a reliable box for kitchen ventilation with your own hands.The main thing is not to hurry and carefully seal each joint of the ventilation duct..

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