Oven and Extractor Hood Installation and Connection

Fixing the duct to the hood takes only a moment. Most of the work goes into planning the route and making the ducting fit the units without compromises. The job usually covers:

• Measuring the route from the hood outlet to the wall or ceiling outlet
• Cutting openings in the base, shelf or top of the wall cabinet
• Fitting the non-return flap and connecting the duct to the hood
• Running the ducting through or above the cabinets and fixing it in place
• Connecting to the wall outlet and sealing every joint
• Covering exposed ducting with a trim strip or panel
• Testing airflow and noise at every speed setting

Core drilling through an external wall and wiring the hood are separate jobs. If there is no socket above the units and a new supply is needed, a qualified electrician must install it.

The fitter starts at the hood outlet and looks for the shortest, straightest route to the outlet. Why does this matter so much? Every bend and every metre of duct resists the airflow. The hood then roars at full power but extracts poorly.

A non-return flap goes onto the hood outlet. It opens when the hood runs and closes when it stops, so cold air and outside smells stay out of the kitchen. Next come the openings in the cabinets. On chipboard it is worth sealing or taping the cut edges so they do not soak up moisture.

The duct should run through wide, sweeping bends rather than tight elbows. With an external outlet, it is laid with a slight fall towards the outside, so any condensation drains out of the building and not back into the hood. Joints are pushed together, secured and taped with aluminium tape. Clips hold the duct in place so it does not vibrate against the cabinets.

Rigid round ducting

Smooth round plastic ducting resists airflow less than other types and runs more quietly. The diameter follows the hood outlet, usually as the manufacturer specifies. It suits any kitchen with enough space above or inside the wall cabinets.

Flat ducting

Flat rectangular channels can hide just above the wall cabinets or behind a cover panel. An adaptor joins the round hood outlet to the flat channel. The cross-section of the flat channel must not be smaller than that of the outlet. Any narrowing shows up as weaker extraction and more noise.

Flexible aluminium hose

Ribbed flexible hose is cheap and quick to fit, so it turns up often in practice. The internal ribs slow the air and create a hissing sound. It works for a short connection of a few tens of centimetres, not for the whole run.

If no outlet is possible at all, the remaining option is recirculation with a carbon filter. No duct is fitted, and the hood returns filtered air to the kitchen. This removes steam and moisture only partly, and the filters need regular replacement according to the manufacturer.

In a block of flats, the hood outlet is not just your decision. Shared ventilation shafts are often designed for slow natural ventilation. A powerful hood connected to such a shaft can push your cooking smells into your neighbours' flats. Before fitting, ask the building management or owners' association whether you may connect to the shaft. Cutting through the façade affects the common parts of the building and needs the owners' consent.

In a house as well as a flat, it is sensible to check a new opening through an external wall or a change to the façade with your local building authority first. Building regulations differ by area, and the authority will tell you whether you need to notify them or apply for anything.

Take particular care with gas appliances that take air from the room and use an open flue, such as an older gas boiler or water heater. An extracting hood creates negative pressure in the room and can pull flue gases back into the home. Never connect the hood duct to a chimney or flue used by a boiler or stove. The usual fix is a fresh air supply, such as an air vent or a window switch that lets the hood run only when a window is open. A qualified, registered gas engineer should assess the situation. If you ever smell gas, turn off the supply at the meter, open windows, do not operate electrical switches and call the gas emergency number for your area or 112.

The simplest case is a wall outlet directly behind the hood with one or two bends in the route. The work is then short and straightforward.

The job takes longer and gets more involved with:

• A long route through several cabinets or along the ceiling
• Cutting openings in cabinets that are already assembled, without damaging doors and shelves
• Little space above the cabinets, which calls for flat channels and adaptors
• Boxing in the ducting with a panel or a suspended ceiling
• An island hood, where the duct runs through the ceiling
• A cold space, such as an unheated loft, where the duct needs insulating against condensation

With a new kitchen, plan the duct route before the wall cabinets go up. The fitter can then cut the openings precisely and avoid later adjustments.

If you already have a finished, approved wall outlet and the hood is mounted and plugged into a socket, you can handle a short connection yourself. Do not drill through external walls and do not touch the electrical installation.

1. Unplug the hood from the socket.
2. Measure the diameter of the hood outlet and the wall outlet, and buy ducting with the same cross-section.
3. Fit the non-return flap to the hood outlet and check that it opens freely.
4. Mark and cut an opening in the cabinet slightly larger than the duct, then tape the cut edges.
5. Cut the duct to length so it is neither stretched nor needlessly bent.
6. Push the joints together and seal them with aluminium tape.
7. Secure the duct with clips so it does not touch the cabinet base or vibrate.
8. Plug the hood back in and test every speed setting.

Before you close the cabinets and put your crockery away, go through these points with the fitter:

• At the highest setting the hood draws clearly and a paper tissue held beneath it is pulled against the filter
• The noise is even, without whistling, rattling or a banging flap
• The non-return flap closes after switching off and no draught comes in from outside
• All joints are taped and no air escapes from the ducting
• The duct is fixed and does not touch doors or shelves
• Openings in the cabinets have clean, covered edges
• The external grille is fitted and sealed, and its louvres move freely
• You have approval from the building management or the building authority, where it was needed