10mm or 15mm fan / centrifugal or axial

[Meerkat1]

I am fitting a new bathroom, with a bath, thermostatic shower and toilet. Can anyone help me make sense of bathroom fan specs? What is best 10mm hole has already been drilled, but will a 10mm fan be adequate? None of them seem to match up to the specs as recommended by that calculation method (multiply the volume - ie 11.5 cubic m for my bathroom - by the number of air changes 15-20x = 180 cubic m apprx???)...bearing in mind that I like a very hot shower... Centrifugal or axial? The hole is located about 1ft away from a window about 1m wide and along the same wall (external). It is also roughly opposite the bathroom door.

 

[RedHerring2]

You won't get much airflow through a 10 or 15 mm hole.
A 10 or 15cm hole however is a different matter.

 

[Meerkat1]

Alright smart Alec! Do know my metric I can assure you! Errrrrrhem...anyway... More to the point then. What do I need?

 

[JohnD]

centrifugal is generally quieter and more powerful than axial.

keep the window closed otherwise the fan will just take fresh air from outside through the window and just put it outside again. You need a flow of air from low down, and going out high up on the other side of the room. So allow an air gap under the door.

Have the fan wired so it comes on every time the light is turned on and continues 10-20 mins after. It will easily take that long for the shower tray and towels to become less wet, but if the fan comes on every time somone goes in to use the loo, it will clear the air and also remove residual dampness.

At 10p per kWh, a 25w fan will run for 40 hours for 10p.

people who won't turn the fan off because they worry about the cost or the low hum get damp bathrooms.