Even if a cooktop extractor cannot be compared to a conventional extractor hood in many ways, there is still one aspect that both types of appliance have in common. Both cooktop extractors and extractor hoods can work in two different ways: with recirculating air or kitchen exhaust air. With both operating modes, the cooking and roasting vapours are suctioned away by the extractor and odours and grease particles are removed safely. However, there is a difference in how the air is channelled: In the recirculating air version, the air that is suctioned away is filtered through a high-quality activated charcoal filter (cleaning and removal of odour molecules) and channelled back into the room. In the exhaust air version, it is carried away to the outside. Which version is best for which kitchen depends on a number of factors – including the surrounding architecture. A comparison of the advantages and disadvantages of each system shows what you need to bear in mind when making your decision.
Due to its basic operating principles every extractor system has different advantages and is so is not equally suitable for every kind of kitchen. A comparison of the most important points of both operating modes will help you to make a decision.
Exhaust air hoods and cooktop extractors guide the moisture generated during cooking out of the room along with the exhaust air. In the case of extractors with recirculating air this is not the case. The latter does remove grease and odours just as the exhaust air system does, but it does not remove steam. For this reason, when using an extractor with recirculating air it is generally important that an adequate exchange of air is guaranteed – either through an open window or automatically using a controlled ventilation system. Here too, in a kitchen exhaust air system it is important that sufficient fresh air can flow into the house, especially when there is a fireplace in the room, whether it depends on the air in the room or not, such as a wood-burning stove, gas heater or coal fire. When the fireplace and extractor are both going at the same time, the low pressure caused by the extraction of kitchen exhaust air can enable hazardous flue gas to enter the room. In buildings with particularly airtight shells, this risk is present even where there are fireplaces that are not dependent upon the air in the room. A window contact switch eliminates this risk. The switch ensures that the extractor can only be switched on when the window is open and so sufficient fresh air can get into the room. The contact switch on the window can be connected to the extractor motor by cable or radio signal. The window contact switch acts as a monitor: it conveys the position of the window sash to the receiver on the kitchen exhaust air system. If the window is open, extraction can start.
A kitchen exhaust air solution cannot always be installed. If the building is new, find out beforehand from your architect whether or not it is possible in your case. Due to the pipework needed and the opening in the wall to the outside, the installation of a kitchen exhaust air system is more costly and time consuming than that of a cooktop extractor in recirculating air mode. Particularly in rented flats, installation of a kitchen exhaust air system is more complicated than that of a recirculating air system. As a tenant, as well as information from the planner, you will need to obtain the landlord’s permission to install the extractor components. At the end of the day, the building must be modified and this must be approved by the owner of the house or flat.
In winter, with an exhaust air extractor, along with the cooking vapours warm heating air is also channelled outside the building. The result: valuable energy is lost. In passive homes or particularly airtight low-energy homes, this can negatively affect the home’s energy balance. For this reason, building experts recommend installing recirculating air systems rather than kitchen exhaust air systems with conventional extractor hoods in highly insulated new builds. In many new builds kitchen exhaust air systems are even prohibited. Contrary to conventional extractor hoods BORA systems work with a relatively low displacement volume, whereby from the outset very little warm air from the room escapes to the outside, however, in airtight buildings recirculating air is often the best option as such buildings generally have controlled ventilation systems. This automatic ventilation allowing the air to enter and exit the room ensures that moisture is safely carried away and, together with a recirculating air extractor, the air in the kitchen remains fresh. In old buildings, on the contrary, kitchen exhaust air is normally recommended. This is because there are often large temperature differences in old buildings, which encourage the formation of condensation. With a kitchen exhaust air system, the moisture in the air is quickly removed to the outside.
To effectively remove odours, when using a recirculating air system, in addition to the grease filter an activated charcoal filter or special recirculating air filter is necessary. When used over a long period of time, the extremely large filter surface of the activated charcoal gradually absorbs less and less odour molecules, until none are absorbed at all. For this reason, the recirculation filter must be changed regularly. This enables the extractor to continue providing fresh air. Please see the service life or operating hours in the operating instructions of your cooktop extractor system.
