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Humidistat Fan Installation

Postby ianbrookes » Thu May 06, 2010 8:14 am

I have been asked to install a Humidistat Fan with timer in a bathroom (zone 2). There is an exisiting lighting circuit via junction box. I am unsure how these fans work, e.g. does the fan come on when it senses humidity ? so what isolator switch do I need and can I use only one switch (isolator outside the bathroom) as the main source rather than having to also have a pull switch inside the bathroom.

The model I am thinking of is the xpelair SL100HT.

Thanks for advice.
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Postby ericmark » Thu May 06, 2010 5:50 pm

The units are normally just line and neutral connection could not be easier to fit. However if you have loo in bathroom they are not allowed. (That is if fan is to comply with building regs) Do remember Part P and these units do have problems where they will not turn off so isolator is required but where located not really a problem. In theory you should be able to see from fan but don't think that's really a big issue.
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Postby sparx » Sun May 09, 2010 5:14 pm

since these operate by humidity and have timer overun they need a permanant feed only however as Ericmark says if wc in room they must also operate when light turns on to comply with LABC regs.

As for isolator switch, a very misunderstood area even by building control!

If the lighting circuit can be isolated and still enough daylight ie window to see to service fan then electrically there is no requirement for any switches locally.

If no natural light then a switch which isolates all poles of the supply local to fan, ie outside door or pull switch inside room is required,

This fan is also only allowed in zone 2 in a room with bath or shower.

regards Sparx
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Postby ericmark » Mon May 10, 2010 9:49 pm

As Sparx points out light in the room does make a difference. Where there is no natural light you can use lights to trigger fan. However if natural lighting then there must be another trigger. It could be simple switch nothing says it must be automatic. A pneumatic push switch would likely comply.

It is all covered in Part F of building regulations which is free download although there is a little in Part J about the problems in removing air causing combustion gases from being drawn into the house even in a different room. And of course Part P for electric bits. There is even a reference to Part L as to heat retention and to read all sections and be sure it all complies as Sparx says even the building inspectors seem to be uncertain as to what is required.

I did fit a humidity control to my fathers bed room shower but I was not impressed and if it needs replacing I think a pneumatic push switch is a far better option.
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