choice of extraction fan for a very damp bathroom

[bowchurchflat]

Need some experts help regarding a bath extraction fan.
Our bathroom has no windows, it is next to the kitchen. Currently we have a Airflow Loovent tm01 extraction fan which was about 1 year old. The duct goes into the kitchen then connected to the cook hood duct which leads to external. The total duct length for the bathroom fan is about 3.6 meters.
We found the fan was not working as efficient as it should. Every time after shower we leave the fan on for about one hour and the bathroom is still very steamy, though the fan has an extraction rate of 111m3/hr.
Is this a simple question of fitting a more powerful fan? Or it's something else need to be looked into?

 

[efficiencyman]

How have checked the actual extraction rate ?
Are you certain there`s not a build up of dust / fluff along the inside of the duct, ( grease from cooker hood will collect fluff along the pipe and block it ) should not have been installed combined. Can it be cleaned through with rods ? Is it possible to run separately to outside ? Can you check the flows to outside ? then if need be consider a more powerful fan

 

[big-all]

is there a 12mm gap under the door you cannot extract air if its no replaced
try cracking the door open about 6mm and see what happens
also check the louvers on the outside cover open at the same time