Vented extractor hood - restrictions on ducting hose length

17 Jun 2011
Reaction score
United Kingdom
We are getting a new kitchen and the cooker will be against an internal wall. The existing cooker hood is vented to an an external fan located on the same wall as it is now against an external wall.

1. We want to keep the existing extractor hood and connect it to the external extractor fan.
2. So I am guessing - it will have to be through a long hose as the extractor fan will be on opposite wall (Kitchen is 10'7x12'6 and the cooker will now be half way down the longer wall and the extractor fan is in the opposite corner)
3. Is there a restriction on the length of the hose? Is there a restriction on where the hose should be located?

Thanks chaps
Sponsored Links
The only restriction is the efficiency/power of the fan. Some mftrs give max lengths in their product details and some don't.

For a long run you are likely to need a centrifugal fan and you should use rigid PVC pipe and not the plastic concertina which :

a) Is very noisy
b) Diminishes the performance of the fan
c) Traps any condensation which forms.
Can you run the rigid PVC pipe that leads from the cooker hood to the extractor fan in the 'plenum space' above the suspended ceiling??

We have a suspended ceiling in the kitchen, I guess (and hope) it has been made to put ceiling lights in and conceal wires or cables - it was already there when we moved into our house so I don't exactly know whats above it.

If there is sufficient space and you can keep the pipe away from any spots, then yes.

You should try and keep a small negative gradient on the pipe, so that any liquid that might form will tend to move towards the exterior vent rather than back towards the cooker-hood.


If space is insufficient for a 100 mm round pipe, you can get rectangular pipes which take up less space in one direction ( and more in another obviously). These will be 3 or 4 times more expensive than the round pipe and can be found on e-bay .
Sponsored Links
There are limitations to what lengths of duct a fan will push air through.

IIRC, 3m tends to be quoted as a typical maximum fro 100mm fans , but centrifugal fans can do more and are more efficient

Bends will increase the effective length of ducting (ie reduce the fans efficiency) as will none-round duct profiles

It all comes down the the fan's rating and size though

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local