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Cooktop extractor: Recirculating vs. exhaust ventilation

06/02/2025

8 min.

All BORA cooktop extractor systems are available in both recirculation and exhaust air versions. Both systems effectively remove steam, odours and grease particles. The main difference is in the airflow:

The best choice for each kitchen depends not least on the structural conditions. In our guide, we explain how they work and help you to make the best choice for your needs.

Contents

Technical difference between recirculation and exhaust ventilation
Advantages and disadvantages of exhaust and recirculation systems
Points to bear in mind when deciding what to buy
FAQ: Recirculation vs. Exhaust

What is the difference between recirculation and extraction in a hob extractor?

An exhaust air extractor channels the air that it draws in out into the open air. The system is linked to an exhaust pipe system with a wall sleeve, which leads to the outside via an opening in the building envelope. This opening can be in the exterior wall, the roof or the cellar.

The system works as follows:

The cooking vapours (steam) are channelled outside through the wall-mounted vent. Backflow dampers in the exhaust air duct prevent outside air from flowing back into the building. Depending on the installation situation, specialised exhaust air accessories such as an external wall, brick or flat-roof vent may be used.

Exhaust air systems are more difficult to install than recirculation systems and are preferably used in new builds. They remove all vapours and odours from the cooking area. Thanks to intelligent flow technology, less warm inside air is expelled from the home than by classic exhaust air or recirculation cooker hoods fitted over the hob.

In our video, you can see the BORA exhaust air system ducting, using the BORA Classic 2.0 as an example

With a recirculating cooker hood , the air remains in the living space. 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. Here’s what that looks like in detail:

The BORA grease filter removes grease molecules from cooking vapours, whilst the BORA odour filter binds odour molecules.

For the BORA Pure product range, there are two high-performance filters to choose from: the GFES eSwap odour filter and the GFESP eSwap odour filter Plus.

Changing the eSwap filter is child’s play – simply do it from the top through the air inlet, without having to remove any drawers or plinth panels.

The odour filters should be replaced after 150 operating hours or, depending on cooking habits, after around one year, to ensure effective extraction performance. By contrast, the ULBF and ULB3X air purification units only need to be replaced after 300 operating hours (approximately 1.5 years) and 600 operating hours (approximately 3 years) respectively

Recirculation systems are easier to install than exhaust air systems and are frequently used in smaller apartments, rental properties and passive houses as well as low and nearly zero-energy buildings.

Thanks to the automatic run-on function, the hob extractor fan continues to run on a low setting for around 20 minutes after cooking has finished. This thoroughly dries out the activated charcoal and binds the odour molecules more effectively.

BORA cooktop extractors With recirculation or exhaust mode

Modular and compact systems –all BORA cooktop extractor systems at a glance

To the product overview

Exhaust air or recirculation: advantages and disadvantages at a glance

Both hob extractor systems have their advantages, which you should bear in mind when planning your kitchen:

System	Advantage	Disadvantage
Recirculating air	Simple & cost-effective installation Flexibility in planning kitchen islands Suitable for passive & low-energy homes Energy remains in the room	Regular replacement of the odour filter is required Humidity remains in the living space
Exhaust air	Low maintenance (no filter replacement required) Humidity is vented outside	Potential energy loss in winter, as warm air is extracted and vented outside Suitable to a limited extent for passive and low-energy houses Structural opening required

Which is better for me: an extractor fan with an external vent or a recirculating extractor fan?

Both systems have their advantages. Our comparison will help you make a decision:

Recirculation mode is the better choice if	Exhaust mode is the better choice if
✓ a straightforward installation is required.	✓ it is structurally possible to install an exhaust system (for example, in a new build).
✓ structural conditions do not allow for an exhaust air system.	✓ steam and moisture are to be completely removed from the living space.
✓ regular filter changes are not a problem.	✓ the system is to be operated with as little maintenance as possible.
✓ No permission has been granted for exhaust air (e.g. in rented flats).	✓ Food is often seared at high temperatures, as smoke cannot be filtered.
✓ Maximum energy efficiency is important.	✓ You wish to avoid having to change the filter.

Points to bear in mind when deciding what to buy

From installation to maintenance, there are key factors to consider before deciding on a BORA hob extractor system with recirculation or external venting. Our checklists are here to help you:

Installation: take account of the structural conditions

An exhaust air solution is not always possible. Please check:

In the case of a new build, whether the pipework and wall penetration for an extract ventilation system are feasible and permitted: In some new buildings, extractor fans are not permitted. The point of contact is the architect or property developer.

As a tenant, you need to obtain permission from the property owner; after all, it involves a structural change that the owner needs to approve.

As exhaust air options are planned on an individual basis , the duct system (BORA Ecotube) and the wall box are not included with BORA hob extractor systems.

You get everything from a single source. The components (cooktop extractor, hob, fan, filter, duct and wall box) of the BORA cooktop extractor systems are perfectly coordinated with one another.

Exhaust air and recirculation system energy efficiency

In winter, valuable energy can be lost through an extractor fan with an external exhaust system, as warm air from the heating is expelled outside along with the cooking fumes.

Please note: Due to the nature of the system, official energy labels are only available for the exhaust air models.

In passive houses or particularly well insulated low-energy buildings, this can negatively affect the energy footprint.

Construction experts therefore recommend that, in new buildings with high levels of thermal insulation, cooker hoods should use recirculation rather than exhaust ventilation.

In old buildings, on the other hand, exhaust air is usually recommended as there are often significant temperature differences in these buildings which favour the formation of condensation.

Maintenance of exhaust air and recirculation systems

To effectively remove odours, when using a recirculation system, a special recirculation filter – an activated charcoal filter – is required as well as a grease filter.

As usage increases, the surface of the activated charcoal filter is no longer able to absorb and bind the same quantity of odour molecules. That is why the odour filter must be replaced regularly.

The standby and operating times are specified in the user or installation instructions for the hob extractor system. BORA cooktop extractor systems provide a timely reminder on the control panel (filter service indicator) when the filter needs changing.

BORA hob extractor systems in exhaust mode are fitted with a grease filter only, but do not have an additional activated carbon odour filter, as cooking vapours are extracted to the outside.

Air exchange in the cooker hood: Take care with fireplaces

Cooker hoods and hob extractors with exhaust mode remove cooking vapours from the room. Nevertheless, it is important to ensure that fresh air circulates here.

This can be through an open window or a controlled ventilation system.

This applies in particular when operating a fireplace, a gas boiler or a coal-fired heating system in the same room – otherwise, the negative pressure created by the exhaust air could draw dangerous flue gases into the room.

In particularly airtight buildings, this risk exists even with fireplaces that are independent of the room air – that is, heating appliances such as wood-burning stoves, which draw their combustion air via a separate supply duct (e.g. an air-flue chimney).

A window contact switch averts this hazard by only allowing the extractor to be switched on when the window is open and therefore sufficient fresh air can flow into the room. Window contact switches such as the UFKS are available from BORA.

Recirculating cooker hoods filter grease and odours, but not the water vapour produced during cooking: It is therefore important to ensure adequate ventilation.

Your BORA partner can help you with planning

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FAQ on exhaust ventilation or recirculation

We answer the most frequently asked questions about exhaust air and recirculation systems here.

Can any range hood be set to recirculation mode?

Many range hoods can be converted to recirculation mode, provided that the necessary filters can be installed. Check the manufacturer's specifications for detailed information.

What do I need to keep in mind when installing an exhaust hood with an exhaust vent?

Keep the exhaust duct as short as possible, and make sure to use the correct pipe diameter, which is specified for yourBORAcooktop extractor system,as well asensuringtight connections. Depending on the installation situation, special exhaust air accessories such as exterior wall, brick, or flat roof vents are used during the initial installation. When installing fireplaces, ensure that they are installed properly by qualified professionals (use Home-In/Out interfaces).

Do you need an activated carbon filter for a recirculating range hood?

Yes, an activated carbon odor filter is essential because it filters odors out of the air before it is recirculated into the room. The filter must be replaced regularly, as it becomes saturated over time and loses its effectiveness.

Can a recirculating range hood be converted to an exhaust system at a later date?

Provided that the structural conditions for breaking through a wall and the necessary conduits are in place, this is generally technically feasible. On the unit itself, onlyafilter unit is removed and replaced with an appropriate exhaust duct.

How does the noise level compare between recirculation and exhaust modes?

Exhaust systemscan beslightly quieter, since the air does not pass through an activated carbon filter. However, this depends heavily on the duct layout, which determines the noise level. Thanks to modern technology, however, this difference is barely noticeable in everyday life—both options allow you to carry on a conversation at a normal volume right next to the cooktop.