The cooker hood has long been more than just an expensive lighting element. In addition to its efficiency, which it provides as an exhaust or recirculation variant, it is of course also the design that makes it interesting for consumers. www.franke.com The most popular solutions currently include headless wall hoods or integrated ceiling fans, but the retractable downdraft hood is also becoming more and more popular.
What function can or must a cooker hood actually perform? The kitchen is one of the rooms in which excessive humidity is generated. Without an appropriate extraction system, the water vapour produced during cooking can condense on walls and window panes.
Due to the greater difference between the inside and outside temperature, these problems are more noticeable in winter than in summer. Since the temperature in the kitchen fluctuates particularly strongly, greater damage can occur here than in other rooms.
In addition, we are not only dealing with water vapour in the kitchen. We have to remove all the vapour, i.e. the mixture of fat, moisture, solids and odours. The more thorough, the better – also in view of the fact that today there are not only closed kitchen rooms, but increasingly more room solutions in which kitchen, dining and living areas merge into one.
Here a “natural air exchange”, which takes place by opening a window – or by air circulation in the house and flat – is no longer sufficient. Since the vapour is thus transported away by unguided air currents, there is no influence on where it is directed. In the worst case, parts of the lawn can be deposited on walls and furniture and then not only in the kitchen.
Only an extractor hood can remedy this. It stands for “dynamic air exchange”. Its task is to remove the fumes by means of a guided air flow and at the same time filter grease, moisture and odours from the air.
Hood technology: Exhaust air or circulating air?
Two different operating systems are available, the exhaust air and the recirculation system. In both cases and as a rule, the cooker hood above the hob picks up and filters the fumes. This provides a remedy against grease particles and odours. However, whereas with the exhaust air system the filtered air is ultimately led outside, a recirculation hood leads it back into the kitchen. This means that the recirculation hood does not have anything at all to counteract the water vapour, the moisture in the air. Other ventilation is then the order of the day.
Recirculating air should only be used if exhaust air technology is not possible, for example, if structural necessities such as wall breakthroughs cannot be implemented (rented accommodation) or if too long pipelines are required (island kitchens). By the way: Air recirculation hoods may not be used in Germany over gas cookers with more than 11kW.
It should also be noted that the odour-absorbing carbon active filters must be cleaned or replaced regularly and that the air flow rate is reduced by the carbon active filter. In individual cases, recirculating air models can also be louder than exhaust hoods.
The fan of an exhaust hood is usually located in the cooker hood itself. However, units with an external fan are also available, which is then mounted on the outside wall, for example.
The metal grease filter, which is also easy to remove for cleaning in the dishwasher, ensures that no grease film is deposited in the kitchen and possibly in open adjacent rooms.
Exhaust air and chimney dependent fireplaces
When operating an extractor hood using the exhaust air method, if not enough air can flow into the room, a vacuum can develop in the area where the appliance is installed and the exhaust gases can flow back into the room.
There are various ways of avoiding this. The simplest solution is to let sufficient supply air flow into the apartment through a tilted window. However, experience has shown that, due to carelessness, the windows often remain closed when the extractor system is in operation, so this solution is not safe enough.
A reliable alternative is to install a contact switch on the window, which is connected to the cooker hood by cable or radio control. When the window is closed, the cooker hood can no longer be operated.
Requirements for the exhaust air technology
However, other conditions must also be met before exhaust air can be used: Both a wall breakthrough and the exhaust air duct are absolutely necessary and the supply air must be guaranteed. The exhaust air duct should be independent of the house ventilation system and be routed to the outside in the most direct way.
The shorter the extraction path, the larger the pipe diameter and the fewer bends in the pipe, the better the effect. Depending on the air flow rate of the unit, the following cross-sectional specifications apply to exhaust air ducts: 125 mm < 500 m3/h air flow rate, 150 mm > 500 m3/h air flow rate.
Also make sure that the wall box is energy-efficient (Blower-Door certificate) or use a system with an external flap that closes automatically when the cooker hood is not in use and thus prevents cold air from entering.
Extractor hood & hob – pay attention to the dimensions
Hob and hood must be harmonize with each other. Only when the type and size of the hob has been determined should the appropriate cooker hood be selected. With cold hobs, such as induction, the fumes are carried slightly to the side. In any case, the hood should be wider than the hob.
With hot hobs and gas hobs, the fumes rise very quickly and almost invisibly due to the high thermal support. For this reason, the hoods can be planned in the same width as the hob. The recommended distance from the hood to the hob is between 65 and 75 centimetres. Especially when using gas hobs, the distance must not be less than 65 centimetres.
Hobs should be positioned centrally under the cooker hood. If individual cooking modules of different types are combined, the hottest should be placed in the middle.
The higher the cooker hood is installed above the cooking zone, the more important it is that it protrudes sufficiently. A distance greater than 90 centimetres between the hood and the hob should be avoided. The minimum width of the cooker hood, at a distance of up to 75 centimetres from the hob, must be at least as wide as the hobs installed below it. To counteract lateral air currents, it is advisable for the hood to have a lateral projection to the cooktop. General recommendation: 5 centimetres projection for wall hoods, 10 centimetres projection for island hoods.
However, the recommended hood width is 90 centimetres for a 75-centimetre wide cooktop and 120 centimetres for a 90 cm cooktop. Head-free hoods should not be installed higher than 75 centimetres from the centre of the hood to the cooking surface. As there is no complete coverage of the cooktop, fume capture is greatly reduced at greater distances. Vapour extraction hoods with edge extraction and a flat design can, however, have advantages in capturing vapours at the edges of cold hobs.
Finally, it is also important in everyday cooking that with the dynamic ventilation mode the cooker hood is started up by the user before the cooking process begins and not only when the kitchen is already loaded with cooking fumes! Once the cooking process is complete, an overrun is necessary to ensure that the kitchen is properly ventilated.