Bathroom extractor

[Pete the Feet]

As JohnD is possibly inferring, a long run of flexible duct will seriously hamper the flowrate through the fan. Flexible ducts whilst handy to install should be used to as minimum as it causes quite a lot of resistance to airflow.

 

[jrussuk]

Sorry to get back to everyone. This is the system I have in the loft. The run of ducting is around 2.5 meters.

 

[Pete the Feet]

The run from the ceiling to the fan is okay but the run from the fan to the outside wall is way way too long. You have seriously restricted the airflow of the fan to what is most likely a negligible amount of airflow. Flexible ducting is good for vibration but use rigid pipe/ducting on a long run or you will render the fan ineffectual.
My advice would be to use a short length of the flexi to connect to a run of rigid plastic pipe. If the diameter of the flexi or outlet from the fan is 4" or 100mm then a piece of soil stack will do hung with a bit of wire from some nails hammered into the rafters. Do not use the semi-flexible ducting as it doesn't allow the same airflow as the rigid pipe. If its a larger diameter than that then a bit of plastic ducting from B&Q if available.
It looks like you have installed a pukka fan. It would be a shame not to realise the benefits with poor installation.

Just had a look B&Q supply 100mm ducting which should be okay but it is in only short lengths. TLC electrical is a firm I use regularly and they deliver fairly fast:
4 Inch (100mm) Vent Pipe In White 2000mm (tlc-direct.co.uk)
Much cheaper than B&Q and good service.

 

[jrussuk]

Great! Thanks for the advice. I only fitted a new fan to the existing ducting. I will replace the long section. Now does anyone know what different ceiling inlets I can get? I really hate the look of these ones.

 

[Pete the Feet]

Careful what you install regarding vent grilles as many are only suitable for low extraction rates and will therefore compromise the air flow rate as does your flexible ducting.

100mm and 150mm Accessories | Vent-Axia (vent-axia.com)

 

[Sonic70]

That long flexi pipe from fan to wall outlet will have water build up in it.