Installing an extractor fan

Participant · 22 Dec 2013 at 14:34

Hi all

I'm shortly going to install an extractor fan in our main bathroom and have a few questions:

1. Can I vent properly through an old water overflow pipe sticking out of the soffits? If so, any ideas how to properly connect the large vent pipe to the small gauge water pipe? The pipe is no longer used as it was connected to an old header tank, which is now redundant as we have a combi. Using this method will save me having to buy a tall ladder and a large circle saw, then having to drill another hole in the soffit.

This is the pipe (the left hand one, as the other one is taking the TV aerial into the loft

):

2. Any reason I can't wire it to the old now-disused 6mm^2 cable that the old electric shower used to run off? It obviously doesn't draw enough current to warrant the cable, but if I replace the fuse in the consumer unit from the shower with a lower rated one for an extractor fan, this should be OK right? I'll get a new ceiling switch for it.

I don't want it running off the lights because more often than not we don't actually need the fan running when we use the bathroom.

Many thanks.

tigerstyle · 22 Dec 2013 at 14:42

Doubt it bro, all those cfms through a 1inch pipe?
can i say pressure drop?

Participant · 22 Dec 2013 at 14:46

Pressure drop as in the pressure created by the fan will be reduced because of the narrower pipe downstream, thereby reducing the extraction rate?

tigerstyle · 22 Dec 2013 at 14:47

In a nutshell, go check the spec of a standard 6" unit from screwfix, its going to blow a lot!

Participant · 22 Dec 2013 at 15:10

OK, cheers. I'll do it properly then

.

This is the proposed site of the switch:

(to replace the switch on the left)

Would this satisfy electrical standards if I put a fan switch there instead of the shower switch, and a 3A fuse in the consumer unit downstairs?

Ignore the flaking paint; that's the next job

.

Nightglow · 22 Dec 2013 at 15:29

If your fitting a ceiling fan, use a rigid flat channel venting kit, don't use the flexible hose.

Installed ceiling fan here,flexible pipe collapsed after a month or two, replaced it with a rigid 100mm rectangular pipe & rectangular to round adaptors to connect fan & to a 100mm round vent in soffit.

Participant · 3 Jan 2014 at 17:55

Nightglow said:
If your fitting a ceiling fan, use a rigid flat channel venting kit, don't use the flexible hose.

Installed ceiling fan here,flexible pipe collapsed after a month or two, replaced it with a rigid 100mm rectangular pipe & rectangular to round adaptors to connect fan & to a 100mm round vent in soffit.

Thanks Nightglow. How do you connect the hard ducting to the fan and soffit vent and ensure an air tight seal? If they just push together with no gasket then surely there'd be air leaks? Also why rectangular pipe, why not just use round pipe then you don't need to bother with square to round converters?

Another question...I'm going to have the fan come on with the bathroom lights for ease. This won't be ideal in the summer when we won't need the lights on but will want the fan running, but hey it's better than having two switches and I don't trust these humidistat ones as everyone says they run on all the time.

Anyway, my question is: now that I don't need to use the pull cord switch you can see in the above image as a fan switch, assuming it's tri-pole, can I use it as an isolator instead?

Most people seem to use a switch outside the bathroom but I don't want that, and since the pull cord switch is already in situ it would save me some work if I could use that instead.

Simon · 3 Jan 2014 at 19:08

Can't you just put on a timer unit and turn lights on the off to start the fan ?

Insomniak · 3 Jan 2014 at 19:42

Simon said:
Can't you just put on a timer unit and turn lights on the off to start the fan ?

Exactly.
Don't worry about switching in the summer. Just quickly flick the light switch on and off and set the timer on the fan to run for around 20 minutes.
Also dont forget to fit a back draught shutter within the duct to prevent draughts.
You connect the 100mm ducting to the vent and fan by using either cable ties or large jubilee clips.

Nightglow · 3 Jan 2014 at 20:28

Participant said:
Thanks Nightglow. How do you connect the hard ducting to the fan and soffit vent and ensure an air tight seal? If they just push together with no gasket then surely there'd be air leaks? Also why rectangular pipe, why not just use round pipe then you don't need to bother with square to round converters?

Couldn't fit round pipe to the eaves,& through the soffit, very tight space, due to the pitch of the roof, so rectangular was the only choice.

Fan came with a length of flexible extendable pipe, just cut a piece off to fit from fan to round to rectangular adaptor, held in place with a cable tie.
all joints were taped with 50mm wide aluminum adhesive tape I had.
Used a elbow 90° bend at the soffit end, & a rectangular vent in the soffit fixed with non solvent gripfill & some self tappers .

Participant · 4 Jan 2014 at 11:58

Simon said:
Can't you just put on a timer unit and turn lights on the off to start the fan ?

Insomniak said:
Exactly.
Don't worry about switching in the summer. Just quickly flick the light switch on and off and set the timer on the fan to run for around 20 minutes.
Also dont forget to fit a back draught shutter within the duct to prevent draughts.
You connect the 100mm ducting to the vent and fan by using either cable ties or large jubilee clips.

I suppose, but then the fan I'm using extracts 240m^3 of air per hour so in the winter when I need the lights on, I don't want the fan running on for another 20 mins after I've left the bathroom as the steam will be clear after 5 mins max. But then something has to give and it won't cost much to run, so I guess that's my solution!

Thanks for the reminder about the shutter. The ducting is going to be rigid PVC like a soil pipe and I'm asking about connecting this to the fan, so not sure cable ties and jubilee clips will help me do that. Sounds like I just need to push them together and tape them?

Nightglow said:
Couldn't fit round pipe to the eaves,& through the soffit, very tight space, due to the pitch of the roof, so rectangular was the only choice.

Fan came with a length of flexible extendable pipe, just cut a piece off to fit from fan to round to rectangular adaptor, held in place with a cable tie.
all joints were taped with 50mm wide aluminum adhesive tape I had.
Used a elbow 90° bend at the soffit end, & a rectangular vent in the soffit fixed with non solvent gripfill & some self tappers .

Cheers for this. So when I'm connecting the rigid PVC pipe to the fan or bathroom vent, I just push it together then tape the joints?

Nightglow · 4 Jan 2014 at 12:38

Some fans outlets will fit straight into the round to rectangular adaptor, others need a short piece of that nasty flexible hose to connect them.

Some of the vents kits offered by Manrose, Easiduct & some others come with a threaded hose connector socket into which you screw that flexible pipe, & then tape for complete air tightness.

http://www.applianceplanet.co.uk/cooker-hood-extractor-ducting/ducting-product/1265-product.html

As for the channel, you just join lengths together into a push fit connector & again tape the joints.
Manrose have vent kits, which have the exterior vent available white, cotwold & other colours to match your brickwork, if you going through a wall.

malfunkshun · 4 Jan 2014 at 13:38

Because it is a bathroom don't forget to notify building control if you are doing it yourself.

Insomniak · 4 Jan 2014 at 13:56

What inline fan are you getting?
Also in the winter if its cleared all the steam before you leave the bathroom just switch the fan off at the isolator switch.

Nightglow · 4 Jan 2014 at 14:55

malfunkshun said:
Because it is a bathroom don't forget to notify building control if you are doing it yourself.

How many peeps actually do, very few if any?

But the electrical work is notifiable, & should be done by someone who is Part P certified electrician, as a bathroom is a special place & is split into zoned areas.

Ceiling in bathrooms can be exempt in certain situations.

LOAM · 4 Jan 2014 at 15:16

Fans with an overrun let you change the length of time it overruns by (15mins is default). If you want one that does you need to connect it via 4 core wiring (switch live, common live, neutral and earth) with the switch live and live broken over a dual pole fan isolation switch.

Participant · 4 Jan 2014 at 15:41

Nightglow said:
Some fans outlets will fit straight into the round to rectangular adaptor, others need a short piece of that nasty flexible hose to connect them.

Some of the vents kits offered by Manrose, Easiduct & some others come with a threaded hose connector socket into which you screw that flexible pipe, & then tape for complete air tightness.

http://www.applianceplanet.co.uk/cooker-hood-extractor-ducting/ducting-product/1265-product.html

As for the channel, you just join lengths together into a push fit connector & again tape the joints.
Manrose have vent kits, which have the exterior vent available white, cotwold & other colours to match your brickwork, if you going through a wall.

OK cheers for that.

malfunkshun said:
Because it is a bathroom don't forget to notify building control if you are doing it yourself.

Will do.

Insomniak said:
What inline fan are you getting?
Also in the winter if its cleared all the steam before you leave the bathroom just switch the fan off at the isolator switch.

Doh yeah that would work! As for which fan am I getting, this is my shopping list so far:

Have I missed anything? The only other thing I can think of is some three core and earth cable, but I can pick that up from Screwfix.

JohnnyG · 4 Jan 2014 at 16:12

If you're going to take the feed off the lighting circuit via a 3amp (or 5amp, depending on manufacturers instructions) FCU & separate isolator instead of using the old shower cable it will just be a modification to an existing circuit (instead of a new circuit) and won't be notifiable if it's outside zones 1 or 2.
There were changes to what's notifiable and not in recent BS7671 updates

http://www.elecsa.co.uk/Documents/Public-Documents/Contractors/Notifiable-Work-in-England-2013.aspx

Participant · 4 Jan 2014 at 16:31

Probably won't bother with the FCU, the lighting circuit is on a 6A circuit from the consumer unit, so the fan circuit would be sufficiently protected already surely? It's just like adding another downlight onto the circuit. But yeah I'm going to use the lighting circuit rather than the shower circuit.

JohnnyG · 4 Jan 2014 at 16:44

You'll have to use a separate FCU as the manufacturers will specify that with either a 3/5amp in, plus a fault in it would take out the lights too, you don't want that.
It's easy & cheap enough (FCU's @£4) to do & the FCU & isolator can be in the loft area.
As it's a timer model, wire it like this -

2 core L/N from lights to FCU
2 core L/N from load side of FCU to 3 pole isolator, bridge L to Perm L on supply side of isolator.
Perm line & neutral from isolator to fan
Switch line to pullswitch in bathroom, then on to fan.

Hope that makes sense