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The construction industry is considered one of the most actively developing. New technologies and materials are gradually replacing traditional ones. For example, plastic air ducts are being used more and more actively instead of metal ones.
Plastic air ducts: what materials are made of
The word “plastic” hides a whole group of materials with different properties and performance characteristics. Ventilation ducts are made from the following plastics:
- PVC (polyvinyl chloride). It has a wide operating temperature range from -30°С to +70°С. PVC air ducts can be installed in unheated rooms.
- PVDF (fluoroplastic). acid-resistant material with a wide temperature range – from -40°С to +140°С.
An example of ventilation from plastic ventilation pipes in the bathroom - PP (polypropylene). Differs in the increased resistance to chemical influences (transfers acids, alkalis, organic chemistry).
- HDPE (low pressure polyethylene). This material is characterized by increased flexibility, it is more difficult to damage it mechanically, but does not tolerate low temperatures.
When choosing plastic air ducts, you should focus on the characteristics of plastics. For example, to connect a kitchen hood, it is better to use polypropylene ducts. If the exhaust air temperature is high, PVC or PVDF ducts are suitable. Polyethylene boxes are quite suitable for distributing ventilation in residential and other technical premises.
Pros and cons, scope
Plastic air ducts are perceived negatively by many, as they are not sure that plastic does not emit harmful substances during operation. It may be that low-quality plastic is unsafe, but even in household appliances there are so many plastic parts that this consideration seems irrelevant. For example, in a kitchen hood with filters, most of the components are made of plastic. And here the most difficult operating conditions are elevated temperature, a large amount of fat, evaporation of chemically active substances.
In general, experts recommend putting plastic on exhaust ventilation ducts. There are no restrictions here. But for the inflow – you need heat-resistant ones, made of special plastic. Especially if the inflow is heated or recuperated.
Where to use
Another reason for not recommending the use of plastic air ducts is problems with the fire department. There were cases that they did not sign permission to use gas equipment if the ventilation was made of plastic. But it was a frame house, and there the requirements are different. If in doubt, it is best to check with your local fire inspector. In general, there are recommendations in regulatory documents.
According to SNiP 41-01-2003 clause 7.11, plastic air ducts can be used in low-rise residential, public, administrative and domestic and industrial buildings of category D. Their must not lay in basements, undergrounds, attics and technical floors, in rooms with standardized fire safety conditions.
Advantages and disadvantages
Plastic air ducts have both adherents and opponents. Their main disadvantages:
- Flammability. Everything is clear here. Only metal air ducts do not spread fire. Although not all plastics burn and propagate flame, such “reduced” flammability materials are expensive. Therefore, plastic air ducts are allowed only in one-story houses.
- The accumulation of static charge, which leads to the accumulation of dust (it can flare up again). In fact, much more dust accumulates in corrugated areas. To reduce its amount, it is necessary to install a plastic duct after the completion of “dusty” construction work and install filters that catch most of the dust. In addition, plastic ventilation pipes are treated with a special compound. It forms a film on the surface that prevents the accumulation of static charge.
An example of using plastic air ducts to connect a kitchen hood - With poor workmanship, thin walls or a large cross section, gaps may form at the joints due to changes in geometry. This can be fixed, but there is such a drawback.
These are the disadvantages of using plastic air ducts. More than enough advantages:
- Easy installation. The presence of fittings and fittings allows you to create a system of any configuration. Plastic is easy to cut, weighs little.
- Due to ideally smooth walls, the air encounters less resistance.
- Easier to seal. For reliability, the joints can be smeared with sealant.
- Modern plastic air ducts are joined using butt locks without overlaps, which reduces resistance to air movement.
- Low noise level. With a capacity of up to 100 cubic meters / min, the air movement is almost silent.
- Not subject to corrosion.
Here is a set of shaped elements that allows you to make a ventilation system of any complexity from plastic pipes
In general, a plastic duct is not the ideal solution, but the ease of installation and good performance outweigh the disadvantages. In general, experts recommend putting plastic on exhaust ventilation ducts. There are no restrictions here. But for the inflow – you need heat-resistant ones, made of special plastic. Especially if the inflow is heated or recuperated.
Also, when choosing, it is worth proceeding from the operating conditions. For example, it makes sense to use a plastic air duct for an exhaust ventilation duct from wet rooms, since galvanized ones are susceptible to corrosion, and stainless ones are very expensive.
Cross section of plastic air ducts and their dimensions
Plastic boxes for ventilation do:
- Round section.
- Rectangular section (rectangles and squares).
Each type is rigid and flexible. Rigid boxes are cast in special molds. Their main characteristic (except for geometric dimensions) is the wall thickness. In order for the plastic air duct to keep its shape, the wall thickness must be 3 mm. Thinner ones bend, thick-walled ones have more weight and a much higher price.
The second type is flexible plastic air ducts. They are made in the form of corrugations. The wire frame is wrapped in a layer of plastic so that the wire itself is sealed in the plastic. Such air ducts are easier to install, as they can be bent at any angle.
The length of one piece of corrugated plastic pipe for pipe ventilation is up to 2,5 meters, so short runs can be made exclusively from one single piece. Installation is very simple: fixed at both ends, laid out along the track, fixed in several places. It is desirable to stretch the corrugation as much as possible – to reduce the unevenness of the walls and the resistance to air flow.
But, even in a well-stretched corrugation, due to uneven walls, air movement is difficult. Therefore, under equal conditions, corrugated ducts are placed larger. In addition, dirt, grease, dust accumulate faster on an uneven surface. The walls are very thin, have very little mechanical strength. Semi-rigid options are more reliable (as in the photo above). They bend worse, but have higher reliability.
Cross section of round plastic air ducts
The most common round plastic air ducts:
- 100 mm;
- 125 mm;
- 150 mm;
- 200 mm.
Both round and rectangular plastic ducts can be large.
But there are also much larger sizes – up to 2,4 meters in diameter – for industrial premises. Round ventilation pipes are sold in sections of 500 mm, 1000 mm, 1500 mm, 2000 mm, 2500 mm.
Section of rectangular ventilation pipes
Rectangular plastic air ducts for domestic use are available in the following sizes:
- height – 55 mm, 60 mm;
- width – 110 mm, 122 mm, 204 mm;
- length – 350 mm, 500 mm, 1000 mm, 1500 mm, 2000 mm and 2500 mm;
- wall thickness – 2-8 mm.
An example of the dimensions of plastic rectangular pipes for ventilation
The larger the cross section of a plastic pipe for ventilation, the thicker its walls make. This is necessary so that the products do not change the geometric dimensions. To save on shorter walls (in Figure a), the thickness can be smaller (2-3 mm, for example), and the wider part (marked b in the photo) is made thicker – 3-4 mm.
Which is better: round or rectangular duct?
What shape of air ducts is best? Round or square? If you take the bandwidth, then better round. In them, vortex flows meet less resistance, the movement of air masses is faster. The rectangular corners remain practically unused. Therefore, rectangular ones are placed with a larger cross-sectional area than round ones.
Despite the worst performance, rectangular plastic pipes for ventilation are more often used. They are easier to hide by letting them low over wall cabinets, for example. Also, when arranging a suspended or stretch ceiling, they require less height, as there are flat and wide models. Even if a false ceiling is not provided and there is nowhere to hide the ventilation duct, a rectangular box at the junction of the wall and ceiling looks better than a round one.
Mounting Features
Installation of plastic air ducts is many times easier than working with metal ones. You can cut plastic pipes for ventilation with a hacksaw with a metal blade or a grinder with a cutting disc. In any case, the cut is smooth, without burrs.
Shaped elements and fastening to the wall and ceiling
For turns, branches, narrowings, expansions, there are special shaped elements – corners, tees, adapters. There are adapters from one size to another, and from round to rectangular. This is useful, for example, if you need to insert a fan. There are couplings for joining two pipes. Everything is assembled even easier than a children’s designer.
Pipes are attached to the walls or ceiling with special clamps. They are also made of plastic, attached to the ceiling or walls with dowels or self-tapping screws. The pipes are simply “snapped” into the installed clamps.
Instead of plastic clamps for fixing ventilation ducts, you can use perforated drywall hangers. If a rectangular plastic pipe is mounted, they are fixed with two dowels / self-tapping screws at a distance equal to the width of the pipe. The remaining edges are bent down, fastened with screws to the sidewall of the pipe. This method is more laborious, but the suspensions are cheaper. But using self-tapping screws is not the best way out. On them, on a piece of screw sticking out inside the air duct, dust will stick in a few years, which will lead to a deterioration in traction. After 8-10 years, a plug of dust forms in place of each self-tapping screw. As a result, ventilation may stop working altogether. Will have to clean it up.
Assembly Features
If it is necessary to fix the air ducts on the ceiling, they are collected in large sections on the floor, after that they are “tried on” on the ceiling, and the installation locations of the fasteners are marked. Having fixed the two sections, they are connected to each other. This is how the whole system is going. Really nothing complicated. It is difficult to design and select dimensions, and you can mount the duct according to the finished scheme yourself without any problems.
To ensure tightness in the system, experts recommend lubricating the joints with sealant. A neutral white silicone sealant is recommended. After drying, it remains elastic and does not crack from vibration, compensates for thermal expansion.
If, when joining two elements of the system, a “pocket” is formed – the plastic adjoins poorly due to a mismatch in geometric dimensions, the joint is also smeared with sealant, and then wrapped with special metallized adhesive tape. In such cases, it is recommended to remove the “pocket” by pulling it up with a self-tapping screw. It’s not worth doing it all for the same reason – a dust plug will “grow” in this place, which will block the air flow.