Bathroom exhaust to old Ridge/Flue vent?

[Coliander]

Currently in the final steps of renovating a late '70s/early '80s Bungalow.
The property originally had a warm air heating system powered by a gas boiler which was vented through the loft space via a 125mm flue and out of a vented ridge tile in the roof.
The old warm air heating system has been decommissioned and I'm currently looking for a solution for venting the exhaust from the shower room.
Would the the old vented ridge tile be suitable for this purpose?

The plan would be to run 100mm flexible duct at ceiling level from the bathroom intake along to the inline fan (which would be located close to vertical to the ridge tile), then run rigid 100mm PVC ducting pipe vertically to the ridge from the fan with a condensate trap connected to the old cistern overflow and a 100-125mm adapter terminating at the ridge vent.

Total length of ducting would be ~4 metres (2 metres of flexible ducting to fan, then just under 2 metres of vertical to roof.

I know the simpler solution would be to core a 100mm hole in the exterior wall directly above the shower room and vent to there, but I don't have a core drill, and want to avoid putting any more holes in the wall than are absolutely necessary!

Any issues with this proposed set up?

Ta.

 

[foxhole]

Why not use 125 fan and make the most of the larger capacity .

 

[JohnD]

I think you will get condensation in the old flue.

Maybe you can wrap it in insulation and turn up the overrun timer so you run warm dryish air through it.

 

[Coliander]

Why not use 125 fan and make the most of the larger capacity .

I previously purchased the 100mm fan back in June, so not really an option to return it and upsize. Coming to the end of the renovation now, so as you can imagine, money is pretty tight!