The difference between recirculation and exhaust air

The right type of cooktop extractor system 

Designing a new kitchen is both enjoyable and hard work. Which colours and materials should be used? What qualities and opportunities does my existing kitchen offer? Which cooktop extractor system should I choose? And is a recirculation or an exhaust air system best? 

Our cooktop extractor systems can be operated in two ways: as exhaust air or recirculation versions. Both are equally as effective at extracting and filtering steam, odours and grease particles but they differ in terms of where they direct the air:  

With recirculation systems, the extracted air is filtered through a high-quality activated charcoal filter, removing the odour molecules before the air is fed back into the room. With exhaust air systems, the air is expelled outside via a duct system.  

The best choice for each kitchen depends on many factors – not least including the structural conditions. We will now take a closer look at each of the versions.  

A detailed look at exhaust air systems 

As indicated by the name, the air extracted by exhaust air versions of cooktop extractor systems is released outside. To this end, the extractor is connected to an exhaust pipe system, which comes with a wall sleeve. The duct system leads outside through a gap in the building.  

The gap does not have to be positioned in an external kitchen wall, it can also be located in the roof or the basement. The steam is extracted straight from the pot or pan and directed through a grease filter, which removes all the oily particles from the air, and then out of a duct system.  

Thanks to the impressive design freedom offered by the customised BORA Ecotube exhaust air duct system, which can always be quickly, easily and securely installed even over longer distances and enables the air to be directed to either the left or the right, you’ll find the right exhaust air solution for any installation situation.  

The odorous cooking vapours, also known as waste steam, are ultimately directed through a wall sleeve in the building and expelled outside as exhaust air. Non-return valves in the exhaust air duct prevent outdoor air from flowing back into the building. Depending on where the system is installed, special exhaust air accessories can be used for the gap to the outside – from an external wall fan through a tiled roof fan to a flat roof fan. 

Exhaust air systems are somewhat more complicated to install than recirculation ones. They are primarily used in new builds. All vapours and odours are removed from the cooking area. As, unlike conventional extractor hoods, all BORA systems use intelligent flow technology rather than a high flow volume, less warm inside air is expelled from the home, thereby saving energy. 

A detailed look at recirculation systems 

When it comes to the recirculation versions of our cooktop extractor systems, the air remains inside the home. The extractor draws away the air contaminated with cooking and frying odours as well as grease molecules, effectively filters it through a grease and activated charcoal filter, and releases the purified air back into the kitchen environment.  

The activated charcoal filter absorbs the food odours from the waste steam from which the grease has already been removed. With a recirculation system, these odour particles do not get back into the room. After a year or two of service life with regular use, the extremely large surface of the activated charcoal filter is no longer able to fully bind the desired amount of odour molecules. The filter will then need to be replaced for the extractor to keep performing with its usual efficiency.  

Recirculation solutions are far easier to install than exhaust air ones. They tend to be the solution of choice in smaller apartments and kitchens as well as rental homes. As the recirculation systems keep the warm air in the house, they are ideal for passive houses as well as low and nearly zero-energy buildings.  

The recirculation versions of the BORA cooktop extractor systems eliminate all problems with excessive humidity. If properly installed in a normal indoor climate, there is no risk of condensation or mould growth. It is useful to leave the automatic after-run function switched on so the cooktop extractor continues to run in quiet mode for about 20 minutes after cooking. This thoroughly dries out the activated charcoal and binds the odour molecules more successfully.