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Recirculating air or kitchen exhaust air? The advantages and disadvantages of the extractor systems

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.

Kitchen exhaust air and recirculating air – the different operating modes in a nutshell

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Kitchen exhaust air

As the name already suggests, the air that is drawn in is transported into the open air by an exhaust air extractor. To do this, the extractor will be linked to an exhaust duct system with wall sleeves. The duct system leads through an opening in the building shell to the outside. The opening does not have to be in an external kitchen wall, but can also be in the roof or cellar. The extractor then suctions the steam directly away from the pot or pan and guides it through a grease filter, which cleans the oily particles from the air, and into a duct system. Thanks to the great design freedom of the BORA duct system (BORA Ecotube), which can be planned over longer distances without negatively affecting the performance of the appliance and which enables air to be optionally channelled to the left or right, a suitable exhaust air solution can be found for every installation situation. The cooking vapours or steam which are loaded with odours are finally guided outdoors as kitchen exhaust air through a wall sleeve in the building shell. Backflow traps in the exhaust air duct prevent air from outside the building from flowing back inside the building. Depending on where the system is installed, special exhaust air accessories are used in the opening – from external wall fans to tiled roof fans to flat roof fans.

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Recirculating air

In a recirculating air system, however, the air remains inside the room. The extractor draws away the air that is loaded with cooking and roasting odours, as well as grease molecules, filters it and returns it into the kitchen. When it comes back out, it is nice and clean. In addition to the grease filter, an activated charcoal filter is also necessary. The activated charcoal filter absorbs the food odours from the cooking vapours from which the grease has already been removed. With a recirculating air system these odour particles do not go back into the room. 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. Please see the service life or operating hours in the operating instructions of your cooktop extractor system. Depending on the system, the BORA recirculation filters have different service lives of between 1 and 2 years. This means that they work for a comparatively long time before a filter change is necessary.
Compared to kitchen exhaust air solutions, recirculating air solutions are considerably easier to install. Especially in smaller flats and kitchens, or refurbished properties, recirculating air is generally preferred.

BORA Classic 2.0 System

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Which operating mode should you choose? Kitchen exhaust air vs. recirculating air

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.

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Assembly

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.

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Energy efficiency

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.

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Maintenance

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.

Kitchen exhaust air vs. recirculating air – the advantages and disadvantages of the systems at a glance

Recirculating air

Advantages:

  • easy and inexpensive to install 
  • can be installed in any kitchen, even in passive and low-energy homes
  • design freedom (e.g. kitchen island can be freestanding)

Disadvantages:

  • the activated charcoal filter must be changed regularly
  • moisture in the air remains in the room

Kitchen exhaust air

Advantages:

  • low maintenance as no filter change is necessary 
  • moisture in the air is transported to the outside with the exhaust air

Disadvantages:

  • In winter, energy is lost as warm heating air is suctioned away and transported outside
  • Only suitable for passive and low-energy homes under certain conditions

Your BORA partner will advise you on optimum planning options

Your BORA partner will advise you on optimum planning options

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