It's time to figure out how the air taken from the kitchen by the hood is removed from the room. This is done with an air duct.
Varieties of air ducts
Air ducts are flexible and rigid.
Flexible duct for kitchen hood
Flexible - aluminum corrugated. Rigid is plastic air ducts for kitchen hood. But they can be tough and air ducts for kitchen hood metal. For example, in various kinds of workshops, box-shaped tin air ducts from tin strips are often welded to order.
Air ducts are round and rectangular. Rectangular ducts for kitchen hood attractive in that they are not as conspicuous as round ones. After all, the furniture in the kitchen is completely rectangular in plan. Therefore, a rectangular pipe among such a headset is easier to disguise.
Rigid duct for kitchen hood But a round corrugated hose-boa with a thickness of 100-150 millimeters, and even shiny in its aluminum nature, will immediately catch your eye!
How to buy air ducts for a kitchen hood
First of all, you need to decide on kitchen hood duct dimensions. In length, it is desirable that it should not exceed 3 m - each meter in excess of this value weakens the draft in the duct by 10%.
Plastic air duct and accessories Kitchen hood duct diameter must not be smaller than the diameter of the exhaust outlet.
As for rectangular air ducts, for hoods with a capacity of 300 m 3 / hour. you need to buy air ducts with a section of 55x110 mm;
For hoods with a capacity of 350 m 3 / hour - 60x120 mm;
For powerful hoods, air ducts with a section of 60x204 mm are used.
It is also advisable to outline the route for laying the duct before buying and mark where and at what angle it will bend. This is necessary to purchase corner adapters (unless, of course, you are buying rigid pipes, not corrugated ones).
Flexible duct and accessories Remember that one turn of the pipe 90º reduces its capacity by 10%. It is impossible to turn the pipe at an angle of more than 90 °: a counterflow of air will be created in it and the operating conditions of the exhaust fan will worsen.
Calculate the total length of the duct. If you decide to use a corrugated air duct, then it should be stretched as much as possible so that the corrugations do not create an additional obstacle to the passage of air.
Price for PVC air ducts for kitchen hoods- about 200 rubles. per linear meter (with a diameter of 100 mm).
Grille for the outlet of the air duct into the ventilation duct Flat ventilation pipes for kitchen hoods are more expensive. For example, with a section of 55x110 mm - about 300 rubles / pgn. m
Corrugated aluminum costs about 100 rubles / pgn. m with a diameter of 100 mm and 185 rubles / pgn. m with a diameter of 200 mm.
It is necessary not to forget to buy another adapter from the hood to the duct and a valve that prevents the air thrown into the ventilation system from re-entering the duct.
Installation of an air duct for a kitchen hood
Corrugated hose is attached to the wall with clamps. Plastic pipes for kitchen hoods themselves have a good bearing capacity. Enough supporting brackets - one for each meter of pipe. Moreover, many homeowners prefer to hide air ducts in decorative boxes or lay them on top of cabinets or mezzanines.
Installation of air duct for kitchen hood Joints should be coated with sealant.
When installing the outlet valve at the end of the duct, make sure that its axis is vertical. If you place it horizontally, then the valve flap will pop under its own weight.
Welded metal air ducts Air ducts are led into the ventilation ducts of a multi-storey building using a special grille. In the upper part, it has a hole for the air duct, the rest is taken up with a conventional grill to ensure natural ventilation of the room.
Air ducts for kitchen hood: photo
plastic duct 
The air duct is hidden behind a stretch ceiling 
Air ducting through the mezzanine 
Placing the duct behind a false wall 
Hiding the air duct in a drywall box 
Ducting over wall cabinets
