How to choose your outdoor vent for a range hood or mechanical ventilation system

The outdoor vent for range hood or mechanical ventilation system is fitted at the end of the network, where extracted air finally reaches the outside. It must do two things at once: let the fan's airflow pass through without choking it, and provide lasting protection for the duct against rain, leaves and animal intrusion. A poor choice at this point in the network can create a restriction that penalises the whole installation by increasing pressure losses.

The choice first depends on where the outlet can be positioned (wall or roof), then on the duct diameter to be connected. Avoid reducing the diameter at the outlet: too small a section speeds up the air, generates noise, reduces airflow and puts unnecessary strain on the fan.

Wall outlet: for buildings with no roof access

When the duct passes through an external wall rather than the roof, several solutions are available. The wall outlet shutter closes automatically when the fan stops, which is useful for limiting unwanted air infiltration. The weather louvre and the mesh end cap protect the end of the duct on a horizontal outlet, while keeping pests out. The square aluminium outdoor grille completes this range for a discreet finish on the wall.

This is often the solution chosen by food trucks and low ceiling premises, when the available height does not allow for a comfortable vertical discharge.

Roof outlet: for restaurants and fixed kitchens

When the network comes out through the roof, the galvanised roof cowl protects the duct from the weather while letting air escape freely, fitted at the end of the vertical duct. The 2 in 1 roof cowl and flashing combines a cowl and roof penetration piece in a single unit, convenient for a quick and tidy installation. For an existing roof or a particular configuration (pitched or flat roof), the roof flashing ensures a watertight seal around the duct, for diameters from D250 to D500 mm. The roof kerb for roof fan, manufactured in France, acts as a fixing base for a motorised roof fan installed on a flat roof terrace.

Dampers: protecting or adjusting airflow

The backdraught damper, manufactured in France, prevents outside air from flowing back into the duct when the fan is stopped, which avoids cold draughts and odours being pushed back in. The galvanised circular control damper has a different role: it allows the airflow in the duct to be adjusted manually, useful for balancing a network with several branch connections. Don't confuse the two: one protects, the other adjusts.

To complete the protection on a roof or wall outlet, the galvanised steel rain flashing collar prevents water infiltration at the point where the duct connects to the roof.

Points to check before ordering

• The exact diameter of your extraction duct, measured on the existing duct or taken from your fan's data sheet.
• The type of roof (flat or pitched) if you are using a flashing or a kerb, to choose the part suited to the slope.
• The outlet location allowed by the building (wall or roof) before ordering an accessory that is difficult to adapt afterwards.
• The presence of elbows, fittings or other accessories just before the outlet, which add pressure losses to be taken into account in the overall sizing.
• The exact function required: weather protection (cowl, louvre, end cap), backdraught prevention (damper) or airflow adjustment (control damper), as these are not equivalent.

Complete with

For your whole extraction network, also check out our ventilation accessories: ducts, fittings and mounting parts.

Need help choosing your outdoor vent?

Let us know the duct diameter, the fan's airflow and whether the discharge needs to be through a wall or the roof. We can then point you towards the outlet and accessories suited to your installation.