extractor fan ducting

[colin36]

Hello people,
I am planning to fit an extractor fan into the ceiling of my bathroom, I have two metal flues exiting through my roof which were once used for a hot air central heating system, which no longer exists, and I am wondering if it would a practical idea to connect the fan ducting to one of these.
It would mean a ducting run of about 4.5 metres from the fan to the top of the existing flue.

 

[NigelKing]

sounds feasible. For duct runs longer than 3m you are best using a pressure developing fan

 

[colin36]

Thank you for the reply NigelKing I now know where I'm heading, I hadn't a clue what a pressure developing fan was but a quick search on the web has brought me up to speed.