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Bathroom extractor fan: inline centrifugal through ceiling/tile vent, or axial fan through wall?

Hi Folks,

I hope to glean some advice before getting an electrician in to install a bathroom extractor fan. Any advice would be amazing, as I'd like to purchase a fan soon to be ready for fitting.

Our bathroom currently has a uPVC cladding false ceiling with downlighters (I don't believe they're correctly rated, but I'll address this when possible), covering a lathe and plaster ceiling in poor condition (plaster has come down in spots due to the moisture-laden air after a shower). There's a window we currently use as our only means of ventilation, but it's clearly not sufficient. So we'll need an extractor fan put in. There's a loft above the bathroom (typical Tyneside 3-bed Victorian house with rear plan pitched roof) so access for wiring and possibly ducting should be fairly easy.

Which would be the better option? An axial extractor fan like a Vent-Axia Centra T going directly through the wall (i.e. 30-40cm) to vent outside, placed above the end of the bath near the ceiling, or an inline fan (e.g. Vent-Axia ACM100T) sited in the loft above the bathroom, ducted to vent through a slate-style plastic tile vent in the pitched roof?

Installing the axial through-wall fan would probably be more straightforward, though it would mean drilling a 100mm hole in tile with a tile/glass holesaw, then core drilling through the plaster and brickwork. It also has a handy quiet trickle mode that would ensure constant ventilation -- useful as we also dry clothes in the bathroom.

Though it looks like it'll be a much better performer on paper, I was worrying if the inline fan will lead to condensation running back to the fan or into the bath (not so much bothered about dripping into the bath, more that it might reduce the lifespan of the fan). As we'd be venting through the roof tile vent, there's no way the inline fan could be sited at a high point in the ducting, as recommended in the instructions -- the fan would be at a midpoint between the bathroom ceiling intake vent and the roof vent (the benefit being we don't need to core-drill through brick -- having a condensate trap that would need draining through a pipe in the brickwork wouldn't be ideal). Or would the decent fan with suitable timer be able to clear any condensation worries?

Finally, is a humidistat really necessary, or would the timers and/or trickle mode on the models mentioned suffice?

Thanks for your help. As you can probably gather, I've been thinking about this issue on my own, so it'd be great to have some insight from the experts!

3 Answers from MyBuilder Electricians

Best Answer

hi , i would say a humidistat fan would be alot better after the 4" hole have been drill its there for life and will work as soon as humidity is detected , so drying clothes would be no problem. hope this helps hills-electrical


Answered 13th Apr 2016

If there is enough space in the sofit i would duct it through there instead of a roof vent. That way an inline fan would be in the heighest point in the ducting. Also fitting cost would be less. Additional benefits would be a reduction in noise .
If fitted above the bath end on the wall, a SELV supplied fan would be needed if it is in zone 1. Humidistats are optional as well.


Answered 9th Jan 2019

Having the duct exit higher than the fan will lead to condensation problems unless the duct run is insulated, kept very short and condensation trap is fitted. Using a humidity sensor switch is a very good option.
Alternative is to use Positive Input Ventillation unit easily mounted in loft solves many ventillation problems any where in house.


Answered 27th Mar 2020

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