A cooker hood extracts smoke, steam, grease and odours before they have a chance to spread round the house. They're indispensable if your home is open-plan, or if you have a kitchen-diner.

Here, we explain how cooker hoods work, and help you understand the choices available in our varied range.

Hoods either vent fumes outside via a ducted hood, or clean air by re-circulating it back through a filter. Ducted cooker hoods will need access to an external wall; re-circulating models use filters that will need cleaning and replacing from time to time. Both types of hood also collect airborne grease that is created during cooking.

As a guide, hoods should be positioned at least 65cm above a gas hob and 43cm above an electric hob.

Hoods and extractors come in many different shapes, finishes, colours and sizes but for optimum performance the hood should be at least as wide as the hob:

Integrated: usually fitted between wall units with a door on the front to match the kitchen cupboards. Inexpensive and undetectable when not in use.

Built in and canopy: the extractor is fitted into the base of a decorative canopy or into a chimney breast. Available in a limited range of sizes.

Chimney and island: these tend to be high tech models that are features in their own right. You’ll need to check your ceiling is high enough and strong enough to take the weight. 

Telescopic: these fit below a small cupboard and slide forward when in use. The motor sits in the cupboard above.  

Vented cooker hoods require ducting to the outside of the house using the correct size ducting, which is determined by the ducting diameter of the hood. Don’t worry if you have to position your hood on an internal wall, as flexible ducting means a hood can be mounted internally but ducted externally by simply turning the ducting through 90degrees. It is also possible to vent a cooker hood into an existing chimney or flue - but the appropriate ducting must still be used.

If you live in a flat or your cooker is too far from an external wall you’ll need to install a re-circulating cooker hood. These extract air, draw it through a grease filter to remove air-bourne grease and then a charcoal filter to remove odours, before pumping it back into the room.  Grease filters will need to be cleaned or replaced every 3 or 4 months, metal filters can be popped in the dishwasher and charcoal filters will need replacing every 12-18 months depending on how often the hood is used.

You must always make sure your hood is powerful enough for the size of room that it will be venting. A hood should be able to change the air a minimum of 8 times an hour, but ideally 12 times per hour.

To calculate the volume of your kitchen multiply length x width x height, then multiply the total by 12, to allow for 12 changes of air per hour.

If your room’s volume was 30m³ the hood would need an extraction rate of approximately 360m³/h.

Anything that’s got a big fan it is going to be noisy, and cooker hoods are no exception. Noise is measured in decibels and before making a purchase you should bear in mind the amount of noise the hood will make.

All new appliances are given a noise level rating, the lower the rating, the quieter the appliance. To put it into context, a normal conversation measures about 46dB and a kettle boils at 42dB, so a hood with a rating of 55-65dB is ideal. If you eat in the kitchen, look for a hood with the lowest noise rating.

• Round pipe ducting: provides optimum airflow.

• Rectangular ducting: an excellent alternative when space is restricted. The low profile means it can be concealed in the ceiling void or run along the top of
wall units.

• Flexible hose ducting: available in round and rectangular form, it’s ideal for when a rigid system cannot be used.