The whole purpose of a cooker hood is to help you to eradicate unpleasant odours, grease and steam from your kitchen and this is achieved in one of two ways. A recirculating hood draws in the air from your kitchen and passes it through a filter which is normally made of activated carbon granules. After filtration the air is passed back into your kitchen, and the theory is that all the contaminants in the air are left behind in the charcoal and only clean air passes through. This is fine up to a point, but unless the filter is extremely efficient some odours can still remain, and moisture is relatively unaffected. The filters have to be cleaned or replaced regularly, and this can be a very messy operation and in practice I am willing to lay good odds that the majority of filters are never changed from one year to the next! However, they are relatively cheap to buy and easy to fit, and since the air remains within the kitchen none of the precious heat in it is lost, which is a very important point to consider in these days of high energy charges and environmental concerns.
The other type of hood, the extractor hood, does exactly what the name suggests; it draws air out of the kitchen and deposits it outside into the open air. As the result of this the air within the kitchen is constantly changed and grease, unpleasant smells and steam are kept well under control. This also means of course that all they precious heat in the kitchen's atmosphere is also pumped away, but then this may be considered by many people to be a blessing in disguise because there are far more kitchens which are too hot for comfort, rather than those which are too cold! Extractor hoods are fairly simple to fit if the cooker is on an exterior wall but far less so if it is against an internal wall. In this case an extractor pipe, very often a flexible pipe made of corrugated aluminium, has to be installed to carry the air from the cooker to an external grill and this can often be quite difficult to fit, since the two choices are usually to run it over the top of the ceiling or around the walls and inside, or on top of, kitchen cabinets. All of these possibilities can create considerable problems under the wrong circumstances, so if you are considering fitting an extractor hood of this type it is essential that you first of all work out how you are going to route the extractor pipe and get a clear idea in your own mind of the benefits and disadvantages of the extractor, and how much it is going to cost you to fit it in terms of both price and disruption.
The best time of course to fit an extractor fan is at the same time as a new kitchen is installed since it is inevitable that a fair bit of work will have to be done to provide an electrical point and it is far easier for an electrician to do this in a room which has been cleared of all kitchen units, rather than have to remove and refit units, which is always a job which sounds much easier to do in theory than it is in practice!
Popular manufacturers of kitchen hoods include Neff, AEG, Baumatic, Hotpoint and Elica; styles include such wonders as chimney, island chimney, conventional, canopy, and telescopic designs; as far as materials go some kitchen designers produce wonderful (and very expensive) Works of Art, some clients are happy with anodized aluminium, and stainless steel is occasionally in fashion, and occasionally out!