Can You have a too powerful Bathroom Fan?

[peterduckett]

Greeting

I'm looking to replace a bathroom fan but im not sure on which size,
L: 2.35m
W: 2.1m
H: 2.3m

which gives a volume of 11.4 CM

Now from what i have read a bathroom with a shower is recommended 15-20 air changes per hour or a fan with 171M3H - 228 M3H

Is this excessive as no 4" fan can meet that spec and generally a 6" is around 280M3H

http://www.tlc-direct.co.uk/Products/SLS300CHZ.html

Would this be too much?

 

[viewer]

No problem using the bigger fan, but to remove 280 cubic metres you need to allow another 280 in to replace it. You also need to avoid air short-cutting to the fan from an inlet. The design and placing of the inlets is key.

 

[ban-all-sheds]

Also, don't forget that as soon as you add backdraught shutters/outlet grilles, ducting (particularly flexible, or containing bends) the performance of the fan will drop.

Couple that with what viewer says about needing to replace the air, and you'll see why you never, IRL, get the performance from a fan which is advertised.

Unless it's pinning animals and small children to the wall, or causing doors and windows to burst open, it's not too big.

 

[securespark]

I turned my bathroom fan on without the grille in place and returned to check it was working while drying my hands. No word of a lie, the hand towel began to disappear up the ducting...

http://www.tlc-direct.co.uk/Products/SLTD500SILENT.html

Now, it is oversized, but there is a 6 metre run of flexi duct, a couple of small bends, and grilles on either end (now!)

But I did slice a couple of inches off the bottom of the door to allow for air replacement, and the grille is as far away as I can practicably get it from the door.

 

[peterduckett]

It will be beside the window at the end of the bath in zone 2 which is also opposite the door which should give it a nice flow of air.

Might have to increase the gap under the door so i need to ensure a rate of 0.07M3 per second

That is almost impossible to get from under a a 2cm gap over 76cm would require a air speed of around 4ms