Another bathroom fan query.

[Sponge]

The current fan in my bath/shower room (no toilet, with opening window) isn't up to the job. We are a family of five and the shower gets used for prolonged periods. Even with door all but closed and window open, condensation is an issue throughout the house and especially in the bathroom.

The current fan is a 100mm timer over-run/humidistat, labelled internally as a Domus H1.

I was thinking about fitting a larger fan and have come across a model with superior extraction rates that is also relatively quiet - the S&P Silent 300 Plus.

My house was fully rewired last year and the electrician fitted the fan.

It runs off the light switch (M&K pull cord inside room) and there appears to be no other means of isolation. In my last house there was an isolation switch next to the fan.

I've been reading the associated paperwork from the manufacturer's website and it states this:

The units are manufactured with double electrical insulation (Class II) and therefore they do not need an earth connection.

The electrical installation must include a double pole switch with a contact clearance of at least 3 mm.

Link

What does this mean with relation to my hope of simply enlarging the hole to accommodate the fan and a like-for-like rewire?[/url]

 

[JohnW2]

It runs off the light switch (M&K pull cord inside room) and there appears to be no other means of isolation. In my last house there was an isolation switch next to the fan. ... I've been reading the associated paperwork from the manufacturer's website and it states this:

The units are manufactured with double electrical insulation (Class II) and therefore they do not need an earth connection.
The electrical installation must include a double pole switch with a contact clearance of at least 3 mm.

... What does this mean with relation to my hope of simply enlarging the hole to accommodate the fan and a like-for-like rewire?

Your present light switch is only single pole, and may or may not have a contact separation of at least 3mm. If you wanted to comply with those instructions, you would probably have to have a separate isolator installed for the fan - converting the present light switch to a double-pole one would probably not be easy, since there will be no neutral going to the present switch.

Kind Regards, John

 

[ban-all-sheds]

The current fan in my bath/shower room (no toilet, with opening window) isn't up to the job. We are a family of five and the shower gets used for prolonged periods. Even with door all but closed and window open, condensation is an issue throughout the house and especially in the bathroom.

I was going to ask if it was a new(ish) house until I saw that it has been rewired.

Have you recently done anything to cut down draughts, like new windows, doors, blocking off chimneys?

 

[ericmark]

In the main fans which don't seem to work are trying to blow out air which has no route to be replaced. There are heat recovery units now which have the heat exchanger built into the pipe. This means a unit very little bigger than a standard fan which draws air in through the same pipe as it blows air out and that air is pre-heated.

So in most cases it is a case of either swap a simple fan for a heat recovery unit or cut lumps of the bottom of doors so it can draw air from the rest of the house and of course in the process produce cold drafts.

Look at this as an example.

 

[ban-all-sheds]

converting the present light switch to a double-pole one would probably not be easy, since there will be no neutral going to the present switch.

The latter is irrelevant.

Even if there were a N there, a DP switch would be no use - wouldn't isolate all 3 conductors.

 

[JohnW2]

converting the present light switch to a double-pole one would probably not be easy, since there will be no neutral going to the present switch.

The latter is irrelevant. Even if there were a N there, a DP switch would be no use - wouldn't isolate all 3 conductors.

I admit that I haven't looked at details of the fan, to ascertain whether there is a "third conductor", but I was basing my comment on the fact that the OP has quoted the MIs as only calling for a "double-pole switch".

Kind Regards, John

 

[ban-all-sheds]

Hmm.... it does, doesn't it.

I sincerely hope that in a bath/shower room which is heavily used the OP will be fitting a timed overrun fan.

 

[JohnW2]

Hmm.... it does, doesn't it. .. I sincerely hope that in a bath/shower room which is heavily used the OP will be fitting a timed overrun fan.

Having looked at the instructions, it depends on which variant of the 'Silent 300 Plus' fan the OP plans to have. If, like his present one, it is humidistat+timer controlled (not light-switch+timer controlled), then there is presumably no need for a 'third conductor'?

Kind Regards, John

 

[ban-all-sheds]

Err...

It runs off the light switch

 

[JohnW2]

Err...

It runs off the light switch

Ah, I forgot that bit - but does it make any sense for an "over-run/humidistat" fan to be "run off the light switch"? I'm getting rather confused!

Kind Regards, John

 

[ban-all-sheds]

Is the overrun humidistat controlled rather than timed?

 

[JohnW2]

Is the overrun humidistat controlled rather than timed?

Don't ask me - but (depending, I suppose, on the switching logic) the concept of having any sort of humidistat fan controlled by a light switch could be at least partially self-defeating, couldn't it?

Kind Regards, John

 

[JohnW2]

Don't ask me - but (depending, I suppose, on the switching logic) the concept of having any sort of humidistat fan controlled by a light switch could be at least partially self-defeating, couldn't it?

OK. The humidistat+timer variant of the 'Silent 300 Plus" is OK - the light-switch operation only over-rides the humidistat at humidity levels too low to trigger the fan - i.e. if humidity is high, the fan will come on (and remain on until timing period after humidity falls to the threshold), even if light is off but if humidity is too low for fan to come on, the fan will come on with light-switch (and remain on for-timed period after the light is switched off - unless then over-ridden by high humidity).

Kind Regards, John

 

[ban-all-sheds]

So it needs a 3C+E supply.

And if an isolator is required, a 3-pole one.

 

[JohnW2]

So it needs a 3C+E supply. ... And if an isolator is required, a 3-pole one.

Yep, that variant would - but we don't know which one the OP is proposing to get.

However, none of this actually alters the bottom line of what I said (and what you picked up on). If the OP wants an isolator, he needs to have one (quite probably a 3-pole one) installed specifically for the fan, rather than try to 'adapt' the light switch.

Kind Regards, John