Extractor fan in bathroom off old shower circuit

[FoxtrotOscar]

Hi all

I'm about to install an in-line extractor fan in our main bathroom. It has a window, but we still get condensation problems as we often have to leave the house very soon after showering for work, so the window doesn't stay open for long enough. It also makes the bathroom freezing and it's only heated by a puny towel heater as it is!

Anyway I have some questions that it would be great to get answers to if possible.

1. There used to be an electric shower in the bathroom, which has now been replaced by a thermostatic mixer off the combi. Since there is now a spare power cable, can I use this to feed the extractor fan rather than spurring off the light circuit? The shower was run from this switch (on the left) and my intention is to use it to switch the fan on and off:

Would I just need to reduce the fuse in the consumer unit to an appropriate rating? What should an extractor fan be fused at?

2. My plan is to use an in-line fan and run the ducting across the attic and vent through a hole in the soffits, probably by removing this old overflow pipe:

Is this sound?

3. Do you have any specific recommendations for in-line fans that will extract a decent volume of air? I don't want one that barely satisfies regulations, I want it to do a good job of reducing moisture in our bathroom.

Many thanks for any tips / opinions / advice.

 

[Taylortwocities]

You REALLY should run thjis off the lighting with a timer fan. Then the fan will be clearing the room after you rush off to work.

If you used the shower circuit then you'd need to fuse it down from its present 40amps isn to 3amps. That would mean an addditional switched fuse somewhere - and the loft is not the best place for a fuse..
Take my advice & use the lighting circuit.

Now, re your fan extract.
You will NEVER get a 100mm hole in that place. There's constructional timber behind that fascia. The grill should go in the underside - into the soffit. Make sure you miss the joist!

See here if you arent sure how ra roof is constructed
http://www.contractorssolutions.com/fascia_soffits.htm

 

[jj4091]

Personally I think replacing your "puny towel heater" with a radiator would help to reduce the moisture more in your circumstances

 

[FoxtrotOscar]

Thanks for the replies. Can't replace it with a radiator as the area isn't wide enough for one. I could get a taller towel heater though I guess.

You REALLY should run thjis off the lighting with a timer fan. Then the fan will be clearing the room after you rush off to work.

Yep, I'm intending to operate a timer fan that comes on with the pull cord switch, and stays off for x mins after the pull cord is switched off. For this I guess I need both a permanent live from the fan as well as a switched live from the pull cord switch.

If you used the shower circuit then you'd need to fuse it down from its present 40amps isn to 3amps. That would mean an addditional switched fuse somewhere - and the loft is not the best place for a fuse..
Take my advice & use the lighting circuit.

OK, happy to take advice, but I'm inquisitive by nature and always ask, so here goes - why must I use the lighting circuit and why can't I use the shower circuit? And why can't I just fuse it down to 3A at the consumer unit? Here's mine, showing the shower circuit:

Now, re your fan extract.
You will NEVER get a 100mm hole in that place. There's constructional timber behind that fascia. The grill should go in the underside - into the soffit. Make sure you miss the joist!

See here if you arent sure how ra roof is constructed
http://www.contractorssolutions.com/fascia_soffits.htm[/QUOTE]

OK, thanks for the useful link. There's a flat part of the horizontal section of the soffit that I think I can use for the vent outlet:

 

[EFLImpudence]

OK, happy to take advice, but I'm inquisitive by nature and always ask, so here goes - why must I use the lighting circuit and why can't I use the shower circuit?

Well, you could; it is just a circuit.

And why can't I just fuse it down to 3A at the consumer unit?

You could.

However, if you want the fan to be timed then you will have to use the lighting circuit.

 

[rjm2k]

However, if you want the fan to be timed then you will have to use the lighting circuit.

Surely you mean "However, if you want the fan to be triggered by the lights then you will have to use the lighting circuit."

It could still be timed and triggered by the old shower switch. I prefer them arranged like that so that I don't set the fan off when I go for a p in the middle of the night.

It's normal to fit these with a 3 pole isolator though, isolation via the MCB wouldn't provide the same level of isolation.

 

[AndyPRK]

It's worth considering a fan with humidity sensor in.
Better than just a timer.

Longer overrun than you would want a timer set to.
Although if your going to use the old shower cord to trigger it not so much of an issue.

 

[EFLImpudence]

Surely you mean "However, if you want the fan to be triggered by the lights then you will have to use the lighting circuit."

Yes, that's what I meant.

It's normal to fit these with a 3 pole isolator though, isolation via the MCB wouldn't provide the same level of isolation.

If you mean because of the remote location, that is true but it is all that would be required.

 

[EFLImpudence]

I think most of this is academic and more trouble than it would be worth.

Are there 3A starbreaker mcbs? I can't find one.

If not, there is no point using anything other than the lighting circuit -
plus you can then use a smaller, easier and quieter pull cord switch.

 

[rjm2k]

As above, use the lighting circuit for the fan and the shower to provide a loft socket.

 

[sparkwright]

Same here, far easier to use the lighting circuit, for any type of fan.

 

[JohnD]

if you are using an inline fan mounted in the loft, it will be very quiet so the benefits of having it run every time the bathroom light is used <parp> outweigh the insignificant cost.

Some people have an aversion to ventilation and will not turn fans on, so expecting them to pull a fan cord is doomed to failure.

 

[FoxtrotOscar]

Thank you very much for your replies. I'm sensing that the lighting circuit is the favoured option so I'll use that for the fan.

The idea of using the old shower circuit for a loft socket is so simple yet so beautiful, I hadn't thought of that. The MCB on the consumer unit for the shower is rated at 40A...do I need to use a FCU for my loft socket? The other sockets are on 32A breakers.

It's normal to fit these with a 3 pole isolator though, isolation via the MCB wouldn't provide the same level of isolation.

Surely flipping MCB would isolate permanent live, switched live, and neutral? What other level of isolation exists?

It's worth considering a fan with humidity sensor in.
Better than just a timer.

Longer overrun than you would want a timer set to.
Although if your going to use the old shower cord to trigger it not so much of an issue.

I've considered these, but everything I read says they trigger at random times, run on for too long, and are just generally flaky. If I could find a reliable humidistat switch that worked with my fan (Manrose MF100T) though, then I might well consider it!

JohnD - it's an inline fan that will be situated on a rubber mat in the lift, so I expect it will be pretty quiet. However, I'd like the ability to turn it off, since there's a big window in the bathroom that will be open in the summer and do all the ventilation that's required without using 30W for 20 mins.

By the way here's my shopping list:

Just need some 3 core and earth and a FCU. I'm thinking a switched FCU could do the job of both the pull cord isolator and the FCU though?

 

[rjm2k]

The idea of using the old shower circuit for a loft socket is so simple yet so beautiful, I hadn't thought of that. The MCB on the consumer unit for the shower is rated at 40A...do I need to use a FCU for my loft socket? The other sockets are on 32A breakers.

That should be reduced to a 20Amp MCB if you put a socket on the end.

Surely flipping MCB would isolate permanent live, switched live, and neutral? What other level of isolation exists?

MCBs are single pole so only isolate Live. If a Neutral to Earth fault developed, flipping the MCB wouldn't help, so unless you have a 3 pole isolator you potentially end up having to disconnect fixed wiring in the middle of the night with no lights (depending on your RCD setup).

The MFR instructions will probably show a 3 pole isolator anyway.

 

[AndyPRK]

I got a manrose humidity one off eBay for £25. Mounts on the ceiling.

Yes it needs adjusting so the cut off is sensible. (But still better than long timer)
And use a manual way of turning it on in timer mode.
E. g light or pull cord.