Wiring bathroom fan from circuit in another room?

[Kaymo]

I need to fit an extractor fan in an upstairs bathroom which doesn't currently have one. It is going to be very difficult to get to the unswitched live from the bathroom light without ripping the place apart, and a timer run on is desired. In any case, the preference is for the fan operation to be independent of the light.

Directly above where the fan will be placed in the ceiling, there is an attic light and switch. First off, is there anything that would prohibit using this to power the bathroom fan?

My first thought was to connect this to the fan, with a pull cord isolator to switch on and off. My concern is that the timer run on would need an unswitched live, which means that there would still be a live on the fan when the switch was off and this could be misleading - i.e. someone could turn off the isolator and think that the power was removed from the fan. In this scenario would I need a second isolating switch in the bathroom? Again, concerned that this could be confusing with respect to which switch isolates the fan.

Alternatively, perhaps have a single isolator in the bathroom and use a humidistat to switch on the fan?

Another option - use an inline fan in the attic, in which case the isolation switch for maintenance could be beside the fan in the attic and the pullcord in the bathroom just provides the on off operation?

Grateful for any constructive feedback/advice.

 

[JohnD]

will this bathroom have steamy showers?

why is it difficult to get at the ceiling rose?

 

[Kaymo]

will this bathroom have steamy showers?

Yes. And shower quite far away from the window.

why is it difficult to get at the ceiling rose?

Its not, but the only wires present at the ceiling rose are the switched live, so fan would only be on when the light is on, no overrun.

 

[JohnD]

Yes. And shower quite far away from the window.


Its not, but the only wires present at the ceiling rose are the switched live, so fan would only be on when the light is on, no overrun.

So where do the wires come from?

 

[Kaymo]

So where do the wires come from?

I'm not sure how this is relevant to my question?

 

[JohnD]

Trying to visualise your layout.

 

[Kaymo]

I've taken down the bathroom light ceiling rose, and the only wires there are the switched live and neutral. These must either come directly from the light switch or from a junction that is not accessible. Directly above is a tiled floor as there is an attic room with showerdroom above. Hence I can't get access to trace this back. It may come direct from the light switch, but no easy access above that either to run a cable from there.

 

[Kaymo]

So having thought about this, my plan is to put fit an inline fan with timer run on in the attic space, taking power from the attic light and the isolator switch can then be positioned next to the inline fan in the attic. Control will be from a ceiling pullcord switch outside of the zones.

I can't think of any safety or regulatory issue, but if I am missing something, would be grateful if someone could let me know.

 

[markyd1]

It will be a permanent live prob red and a switched live prob black with no sleeving at the switch not a neutral and where is the earth?

 

[oldbutnotdead]

Sounds ok from safety etc. POV. You might get a bit of noise nuisance for the attic dwellers when the downstairs shower is in use, be careful with mounting fan, avoid Flexi ducts if possible

 

[Kaymo]

Sounds ok from safety etc. POV. You might get a bit of noise nuisance for the attic dwellers when the downstairs shower is in use, be careful with mounting fan, avoid Flexi ducts if possible

Thanks. Shouldn't be a noise issues as fan comes through into a storage part, and the attic is a spare room anyway so normally unoccupied.

What's the reason to avoid flexi ducts?

 

[danechip]

Just trace back from there the lighting fixture is to a joint somewhere.

Flexi ducts vibrate and make noise.

 

[oldbutnotdead]

And flexis collect fluff and all sorts in the corrugations, as well as restricting the airflow.
Make sure you insulate the duct and fan or you'll get condensation in the duct

 

[Kaymo]

Just trace back from there the lighting fixture is to a joint somewhere.

Can't trace back. Mentioned earlier in thread that it goes under tiled floor, which is why I am taking from the attic light.

And flexis collect fluff and all sorts in the corrugations, as well as restricting the airflow.
Make sure you insulate the duct and fan or you'll get condensation in the duct

That makes sense. Unfortunately I can't fit a rigid pipe into the space between the attic floorboard and ceiling below. I checked out rigid fittings and couldn't see any that would fit so I have stuck a flexi that came with the extractor kit on for now. I could run rigid from the outlet of the fan, or possibly swap out the inlet flexi for rectangular ducting - will look into that.