12V extractor fan - fitting to mains socket in loft

[SenileGit]

Hi, I want to fit an extractor fan to my second bathroom. I paid about £180 for an electrician to fit one in my other bathroom a year or two ago, and I am hoping to fit one myself and save money. I see that there are 12v extractor fans available, Toolstation do one for around £35. It comes with a 12v transformer. In my loft there are two mains sockets on one of the crossbeams, these were fitted by a different electrician some years ago, so I presume they are safe. (I have used them with a vacuum cleaner in the past, with no problems.)
I want to connect the 12v transformer for the extractor fan to one of these sockets using a standard plug with a 3A fuse, and then some 12v cable to a 12v PIR sensor, which I will fit in the ceiling of the bathroom, and thence to the 12v extractor fan. The 12v PIR sensor has a timer, so I can make the extractor fan run on its timer, after I leave the bathroom.
Is it legal for me to do this? Or do I need an electrician, in which case I might as well have a 240v extractor fan running off the light circuit.
I presume that a 12v extractor fan is safer all round?
I was also wondering why almost no extractor fans use a simple, dirt cheap PIR detector to turn themselves on? I have seen one on Ebay, but it was 240V and about £80. Wouldn't it be easier to install an extractor fan that didn't have to be connected to the light switch/circuit in some way?

 

[RandomGrinch]

Hi,
There is absolutely nothing wrong with you attempting this installation as a DIY'er

Just be aware of where you install the transformer in the loft.
I believe it is IP rated so a little moisture won't affect it.
But if possible, mount it properly - don't just lay it on top of the loft insulation, or cover it in the stuff!
...and keep it as accessible as possible.

As for the PIR, perhaps people don't like the idea of a sensor 'spying' on them when they go to the loo!

If you have a link for the 12v PIR, we can have a look to check its suitable.

 

[sparkwright]

Yes, fan transformers can fail quickly in lofts - for some reason.

I think the heat, the cold, the condensation and the loft insulation may contribute to this.

I try to fit them away from the loft, such as in a nearby airing cupboard or fitted wardrobe, failing that on the landing above the bathroom door.

 

[Taylortwocities]

Normally, 12v fans are not needed in a bathroom unless the fan is in or very close to the shower/bath etc. see BATHROOM ZONES

If the location is not a zone issue then I would opt for a mains fan and PIR, or powered and switched from the lighting circuit. It easier to do, has less components and removes the need to have a transformer that would need to be powered 24hours a day 365days a year.

 

[RandomGrinch]

and removes the need to have a transformer that would need to be powered 24hours a day 365days a year.

Yes, it is another complication, and a power supply running 24/7; but with items such as aerial amps, USB chargers in sockets, most smart devices, equipment left on standby, etc. It's not uncommon to have these things powered on continuously.

Which doesn't say much for energy efficiency, but that's what we are used to in a modern home!

Even mains fans with a humidistat will have some sort of built-in PSU running 24/7, to enable monitoring of the sensors and energizing of the fan; failure of the PSU in this instance would mean replacing the whole fan unit, rather than just the power supply.

 

[SenileGit]

Hi everybody, many thanks for your help. To answer a few of your questions: I would be fitting the transformer to a wooden cross beam in my loft, which is about five feet off the ground, on the same beam that the main sockets are mounted, so I think they will be okay. It's a walk in loft as I have a dormer extension with a bedroom and bathroom, so the loft is really easy for me to access, and there shouldn't be a moisture problem.

This is the 12v PIR detector I was going to use:
https://www.ebay.co.uk/itm/173429516959
It looks like it will mount very nicely in the ceiling, and has adjustable timer and (presumably) sensitivity dials on the top, so they will be easy to access from the loft.

I'm not sure if it can support sufficient amps - I imagine any 12v fan will probably be using less than 30w? So 2.5A max going through the PIR?

Taylortwocities - the only reason I am considering a 12v fan is because I hope I can fit it myself, thus saving £150 odd. Re powering the transformer 24/7, I can also fit a pull cord in the bathroom ceiling and wire a lead from the mains socket to the pull cord, and thence to the transformer (which will be mounted on the wooden cross beam away from the loft insulation.) The thing is though, I want the fan to run on a timer so that after I have a shower before going to bed, I can just get out of the shower and leave the bathroom, with the fan pushing the moist air outside for five or ten minutes, so I think I won't use a pull cord and will just leave the transformer on all the time, I presume it will only be wasting a watt or two when the fan isn't in use, and it will help to warm up the loft in the winter!


But if I don't legally have to use an electrician, then I might fit a 240v fan instead as you suggest, Taylortwocities, I can easily get to the lead that powers the bathroom light, and I presume I have to fit an isolation switch outside the bathroom too, which I think I'm capable of. And if I am going to do that myself, I may fit an inline fan in the loft instead of a ceiling fan, because I presume they are quieter for a given amount of airflow, than ceiling fans?

 

[flameport]

What is this obsession with a 12V fan? Not needed and just adds extra complexity.

230V fans are readily available.
So are 230V ceiling mounted PIRs, such as this: https://www.toolstation.com/3600-ceiling-pir-single-sensor-ip20/p65562

Far better than a PIR which ships direct from China, takes 2 months to get here and will be of unknown quality.

 

[Taylortwocities]

But if I don't legally have to use an electrician, then I might fit a 240v fan instead

If the fan is located outside the bathroom zones (eg on the ceiling) then the work is not notifiable and an easy DIY project.

 

[RandomGrinch]

What is this obsession with a 12V fan? Not needed and just adds extra complexity.

Hi Flameport, I totally agree.
However, rightly or wrongly many DIY'ers are far more comfortable dealing with low voltage (ELV! ) equipment.
There are also factors such as availability of trades at the moment, and the self satisfaction of doing a job yourself within your ability.
Most of us on here are comfortable wih mains voltage, when others are not.
Sometimes comments on forums like this don't help encourage people to choose the best method of doing things, especially when some (we all know who!) argue about semantics!

There's nothing fundamentally wrong with using a 12V fan, it's just we wouldn't choose to use one ourselves.

 

[EFLImpudence]

...and an isolator is not mandatory.

 

[SenileGit]

Thanks for your further replies! I think I will go for 240v then, and not use an isolator if I don't have to, much less work for me. I am thinking of going for a 240v inline fan then, I have lots of insulated ducting which I bought for the other bathroom's fan, I had to buy 10m and only used about 2m of it. As I say, I have a walk in loft, so access to the bit above the bathroom is no problem at all, and I can easily inspect my work any time I go in there (which is most days.) Thanks for all your help.

 

[RandomGrinch]

That should be a very good solution!
Let us know if you have any problems!

 

[SenileGit]

I've found the fan I think I will go for - I take back what I said about there not being many fans that have sensors built in - I was looking at 12v fans before, this one I've found is dirt cheap and will presumably make the wiring simpler, because it doesn't use the light switch to turn it on:

https://www.ebay.co.uk/itm/164172731863?hash=item26397515d7:g:iXIAAOSwv-1eouZT

My ducting will be about 50-70cm long, I think, so I think this will be a powerful enough fan.

 

[EFLImpudence]

None of them uses the light switch to turn on if you don't want it to.

 

[SenileGit]

Do you mean none of the sensor operated ones use a light switch to turn on, or all other types as well?
By the way, (to everyone), my bathroom doesn't suffer from damp, as I normally leave the window on the ventilation latch (it's a long, 1.5m wide by 25cm high uPVC opener at the top of the main, non-opening window), but I always fully open the window after having a shower and have to stand there for five or ten minutes while I wait for the air to circulate a bit. This is why I am going to fit an extractor fan, so I can just finish my shower and go to bed immediately.
I noticed that the microwave sensor fan I linked to above says the following:
"To be wired with standard twin and earth. Requires only 1 LIVE. No need for switchable live."

So presumably this will be even simpler for me to add to the lighting circuit. I have read on comments on videos on Youtube that you do have to fit an isolation switch - I am in the U.K., are you talking about the U.K., EFLImpudence? I would always turn off all the electricity in the house whenever I do any electrical work anyway.