Have I got this right? Re extractor fans...

[JPE23]

I need two extractor fans, one for bathroom and one for utility room.

Bathroom needs minimum 80L per second
Utility room needs minimum 100L per second

I can't have inline because my roof doesn't have a big enough soffit, and I can't remove roof tiles just because, so my only options are wall fans. Most wall fans are low powered, so it's looking like I'll need something like a 9 inch Manrose...have I got these thoughts correct?

 

[RandomGrinch]

Bathroom needs minimum 80L per second
Utility room needs minimum 100L per second

I wondered where you are getting your calculations from?

I believe the minimum ventilation requirements from Part F, are quite a bit lower...

And if, for example your utility room was constantly in use and 'wet', you could use continuous ventilation, recommended at only 8l/s

However, ideally, we would all be using heat recovery systems, but that's another story!

 

[EFLImpudence]

Part F merely states:

I need two extractor fans, one for bathroom and one for utility room.

Perhaps your house already has adequate ventilation and you don't need any fans.

 

[ericmark]

Neither my bathrooms or utility rooms have fans in this house, and not had a problem. There is one for the kitchen. In the main the problem is with showers allowing the moisture to circulate around the room, if the shower cubical seals top or bottom there is not much of a problem, but if open top and bottom the chimney effect circulates the moisture throughout the room, also fans can cause the circulation so depends much on room design.

My utility room since moving to a heat pump drier has dried up, the problems with damp were more due to leaving the window open and getting too much ventilation with damp air from outside with an unheated room.

Also how long it is running for, units like this can run 24/7 as air going out heats air coming in, as @RandomGrinch has pointed out, although little point with a unheated utility room.