Venting Hob Installation Options

A number of questions arise when it comes to the venting hob installation process. Does it need to be adjacent to an outside wall? Is there a need for lots of ducting?  Can it be installed in a room with poor ventilation. The simple and short answer to these questions is no!

The ideal location for a venting hob is the middle of a well ventilated room. Venting hob installation should not be carried out next to a door or window.

kitchen island integrated hob ventilation

Our advice is to hire an approved kitchen installation technician. We recommend a qualified gas fitter as they will possess the necessary tools and ventilation experience to complete the work safely. If in any doubt you could simply hire us! We have a team of fully qualified fitters and engineers to carry out the work for you.

For the purpose of this guide we will be using the Bosch PXX875D57E venting hob as an example, which we have on display at our Nantwich & Whitchurch showroom

bosch series 8 induction hob integrated extraction PXX875D57E

The Bosch PXX875D57E Series 8 induction hob is framed and has a fully integrated 80cm extraction surface mount.

  • The induction hob with integrated ventilation module: combines best induction with best ventilation technology for perfect results.
  • Integrated ventilation module: extract steam and cooking odours at the source.
  • DirectSelect Premium: spacious and intuitive touch interface.
  • FlexInduction: more flexibility on your hob for large pots and pans.
  • PerfectAir sensor: Automatic control of the hood settings for maximum extractor performance with minimal noise.
  • PerfectFry: no more worries about scorching.

Ducted outside (extracted) vs Recirculated

As with most extraction systems, such as cooker hoods, venting hobs like the Bosch PXX875D57E appliance can either be ducted outside or recirculated. We will explain the differences between extraction and recirculatory in depth later on this page.

For now here is a simple illustration showing the very basic differences.

extracted vs recirculated air

Ducted Venting Hob Installation

The ducted to outside method will usually give you a better extraction rate. In the case of the Bosch PXX875D57E model, ducted out will give you 622 m3h (cubic meters per hour) as opposed to 615 m3h if the recirculatory method is chosen. If you have the opportunity to duct to the outside then we recommend you choose this option.


Ducted outside has its obvious challenges. Ducting will need to run from the hob to a vent on an outside wall. A hob on an island can make this task difficult, but not impossible. A timber floor with a sufficient cavity beneath is the easiest to work with.

For solid stone or concrete floors excavation of a channel will be required to accommodate the ducting. Please remember to keep bends in the ducting to a minimum to maintain sufficient airflow speeds. A maximum distance of 8 meters ensures effective extraction rates.

When deciding whether or not to duct outside from your kitchen it ultimately boils down to budget and practicality.

Hob unit location

Locating your venting hob installation adjacent to an outside wall removes the need for underfloor ducting. Its no longer an island but at least it means that ducting to the outside will be a more straight forward installation.

For 60cm standard depth units 99mm of space is required for ducting to run down the back of the unit. This restricts the depth of drawer units in the island. To accommodate for deeper drawers a deeper 70cm unit will provide the extra 10cm depth to run the ducting.

Ducted Out

The ducted out method will remove heat, moisture, grease and odours produced when cooking and expel them out of your home.

Extraction rates are better compared with recirculation. Test results produced 615m3h for recirculation and 622m3h for ducted out.

Ducting out minimises cooking odours and removes grease from your kitchen units and walls. This method will also remove excess cooking heat and household smells and cleaning detergents.

An effective kitchen ventilation system in your kitchen will improve air flow, clear away smoke, extract hot air and replace it with cooler clean air.


ducted out extracted diagram
An improvement of extraction rate over recirculation modes.

Recirculatory Venting Hob Installation

The most common venting hob installation method is recirculation. Its by far the easiest for kitchen islands and therefore the most cost effective. For this reason Bosch have worked hard to perfect the system to give you the best results possible.

There are 3 methods of recirculation for this hob; unducted, partly ducted and fully ducted. We will explore these in detail below.


Unducted Recirculation

Easy and quick to fit, will fit in a 60cm deep (standard) work top, even if there are full depth drawers below.

The air vents into the void which is present on most kitchen furniture. Min requirement is 25mm but 50mm is recommended.

There is an automatic run off with the extractor fan (minimum power) which dries the service void removing any potential moisture left behind.

A large scale filter surface with high odour reduction capabilities and a lifetime of 360 hours of cooking.

Do not use this method on uninsulated walls.


unducted recirculation diagram
Full Depth Drawers Possible

Partly Ducted Recirculation

This method takes a duct out, from the back of the hob and runs just below the plinth. The air then ventilates into the plinth cavity.

This method is suitable for uninsulated walls or where there has been a previous problem with damp.

You will need to buy the ducting kit to go with this appliance. Also, the drawers below will have to be shallow depth or use a 70cm deep worktop.

The void at the back needs to be a minimum of 80mm.

A diffuser element that directly connected to the flat duct elements spreads the out flowing air in the plinth area for partly ducted recirculation configurations.

partly ducted recirculation diagram
Maximum drawer depth 513mm with 70+ worktop

Fully Ducted Recirculation

This offers exactly the same benefits as the partly ducted method but the pipe extends below the plinth and comes out of a grill in the plinth.

Bear in mind that warm air will blow out of this and can be annoying when you are stood at the hob. If you have the opportunity to vent it to the back of the island it can be better.

If you want to see this particular system in action we have one “live” on display in our Nantwich/Whitchurch showroom. Please call in for a demonstration and we can tell you about all the other amazing features that this hob has to offer.

Design note; if you are running the ducting under the cabinet plinth in order to reach an outside wall make sure there are no floor mounted appliances in the way, such as a fridge, dishwasher and so on. If there are consider making the run 70cm, as opposed to 60cm deep. This will allow you to run the ducting behind the appliance.

fully ducted recirculation diagram
Maximum drawer depth 513mm with 70+ worktop.

Witten by Robin Holt on | Tagged: Extractors,