How to choose your duct fittings

Duct fittings are used to connect each part of the extraction network: commercial kitchen hood outlet, extraction fan box, straight ductwork and direction changes. If poorly chosen or badly assembled, they create air leaks and pressure losses that reduce the actual airflow of the fan, even when it is oversized on paper. The choice depends first on the duct diameter to be connected, then on the function required: network start point, straight connection, diameter change, branch or airflow adjustment. All our parts are made of galvanised steel, robust against moisture and grease from extraction systems.

At the hood or fan box outlet: spigot and collar plate

To start a network from a commercial kitchen hood or an extraction fan box, two galvanised steel parts manufactured in France do the job: the flat spigot, designed for direct hood/duct connection, and the collar plate, with a wider base that better supports the weight of the duct and the airflow at a fan box outlet. For a hood outlet fitted with a double-inlet centrifugal fan, the collar plate is strongly recommended: it makes installation considerably easier, whether for roof or wall cutting or for the final sealing of the assembly. The circular spigot completes the range for round outlets.

Connecting, branching and reducing: the linking parts

A galvanised male connector and female connector allow a duct to be extended or connected to another part of the network (elbow, tee, reducer): the flat spigot is a male part, so it needs a matching female connector to receive an elbow. The reducer allows a change from one diameter to another without straining the duct, and the 90° tee creates a branch to serve a second extraction point. The flexible connector deserves particular attention: it is mainly fitted at the inlet and outlet of a motorised fan box, to limit the transmission of motor vibrations to the rest of the network. It also makes maintenance of the fan box much easier, since it allows it to be disconnected from the network without dismantling everything.

Changing direction and adjusting airflow

To work around an obstacle or turn a corner, the galvanised 90° elbow and 45° elbow, guaranteed for 1 year, allow you to turn without adding unnecessary duct length. However, each additional elbow adds pressure loss: it is best to limit their number along the most direct route possible, especially if the network is already long. The circular damper is fitted to balance or manually adjust the airflow at a specific point in the network, useful when several outlets share the same fan box.

Range parts and their function

Points to check before ordering

• Exact diameter of each end to be connected: a poorly sized fitting leaves gaps that encourage air leaks.
• Male/female orientation: check which part is male and which is female before assembling the spigot, connector and elbow, so you are not left stuck during installation.
• Number of diameter changes and elbows along the route: each one adds pressure loss, reducing the actual airflow available at the end of the network. A long run with many elbows always performs worse than expected on paper.
• Sealing of the assembly: complete your fittings with suitable clamps and seals to avoid air leaks at the joints.
• Weight and fixing: a collar plate supports a heavy duct better than a simple flat spigot, so choose according to the outlet configuration, particularly at a double-inlet centrifugal fan outlet.

Need help choosing your duct fittings

Let us know the diameter of your duct, the fan's airflow rate and the network configuration: length, number of elbows and any diameter changes. We can then guide you towards the fittings and accessories suited to your installation, whether it's a single replacement or a complete network to assemble. Find our video installation guides on our YouTube channel, and our full range of ventilation accessories.