In short, it all depends on how your ducting system has been designed. It is possible. There are many variables, the duty of the fan, where the reducer is situated within the duct run etc, etc.

A reducer is a fitting used in ventilation systems between two pipes of different diameters. Concentric reducers adapt the pipe and enable a change of diameter on a duct run to assist air flows. An eccentric reducer has an edge that is parallel to the connecting pipe and creates an offset in the centre line of the ventilation duct run.A concentric reducer, is shaped like a cone and the centre line is directly in the middle of the two diameters. Be aware that a negative change in diameter can have an impact on the airflows within the duct system, as the air is forced through a smaller area it can create more resistance and more noise. Reducers up to 315mm diameter are pressed reducers (for Standard Sizes), 355mm and above are fabricated reducers. It is advisable to only use reducers to make adaptations to the duct diameter if it is absolutley essential. What is the most common common size of ducting reducer?

Reducers can also be used as enlargers i.e they can be used to increase the diameter, this can have the added effect of reducing the resistance and noise levels. Flexible Drainage Adaptors and Reducers offer a versatile solution for connecting pipes of different diameters. These special couplings are available in a variety of size ranges to suit most applications and are easy to install without the need for special tools or equipment. I have used Fastlec three times each time I have found them to be efficient fast and happy to give you information on their products."

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Reducers for spiral ducting are all male fittings and fit directly into circular spiral ducting (secure using recommended fixing methods). Please Note: Under current regulations, Flexible Adaptor Couplings and Reducers are prohibited for use on adopted drainage systems. Straight Connection couplings with a shear band should be used instead to ensure the connection is protected under earth loads. If a connection needs to be made between drainage pipes that have different outside diameters, combine a Shear Banded Coupling with a Flexseal Bush or Multibush. They are either pressed or fabricated. The majority of pressed reducers are in the size range upto 315mm diameter, however some sizes within this range (which are classed as non-standard) will be fabricated. Diameters from 355 upwards are fabricated i.e a specialist metal worker will make them with there own fair hands. A concentric reducer is a basic peice of metalwork that is used as a duct adapter to decrease (or increase) diameters of a duct system.

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These simple yet effective connectors can be tightened onto pipes of different diameters using a nut driver and torque wrench, creating an airtight and watertight seal in just seconds. The robust design of Flexible rubber drainage adaptor couplings and reducers allows them to connect plastic drainage pipes to other drainage materials such as clay, concrete, stainless steel, cast iron and pitch fibre. This makes them suitable for use with both traditional and modern pipe systems. Our Flexseal & Mission ranges of Flexible Rubber Drainage Adaptor Couplings and Drainage Pipe Reducers are designed with a stepped moulded sleeve that allows them to connect two unadopted drainage pipes together that have different outside diameters – connecting pipes with a larger diameter to pipes with a smaller diameter and vice versa. Each end of a drainage adaptor coupling or drainage reducer has a stainless-steel clamping band used to create a strong seal between the pipe and the coupler.