Controlling a bathroom humidistat fan

Hi all,
I’m planning on putting a fan in my bathroom which gets pretty steamy after a few showers, especially now the air temperature is dropping. I can’t see much point in having it controlled from the light switch – often when someone is showering it’s daylight so the light is off, and often when someone goes in there after dark they don’t want a shower and I don’t want the fan to start whirring.
So (failing some direct link from the fan to the shower mixer) humidistats seem the best solution. But from what I’ve read from the archives they can be a pain because they can get triggered by changing outside atmospherics. Because it seems that this is partly caused by outside air blowing in through the fan I’m thinking of having the fan controlled by an separate humidistat which I would mount on the wall close to the shower area. This one would probably do the job: http://xsls.com/?739
I’m planning on getting a 6” fan because it’s a pretty big bathroom (5m x 2.5m x 2.3m). I was thinking of vent-axia’s basic Silhouette 150X (no timer, no built-in humidistat).
http://www.vent-axia.com/awwebstore/products/domestic/silhouette.asp
I would connect this to be controlled by the external humidistat (which has its own overrun timer to prevent cycling). I would also like to add a ‘three-way’ switch which I could use to turn the thing off completely when I never want it on, to set it to humidistat control (which is where I would normally leave it) or to have it permanently on (for situations when the humidistat was not calling for ventilation, but when I want it on anyway).
Two questions:
1. Does anyone have any idea where I could get a suitable switch (ideally one which would serve to isolate the fan for servicing as well, although if I had to have a separate FCU that would be OK).
2. How would I actually go about wiring all this up?
Alternatively if anyone knows a ready-made fan with this level of control which doesn’t work off a switched live from the lighting I’d love to know about it.
Many thanks,
Martin
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Hmmmm, sorry about that, let's try again ...
Hi all,
I'm planning on putting a fan in my bathroom which gets pretty steamy after a few showers, especially now the air temperature is dropping. I can't see much point in having it controlled from the light switch - often when someone is showering it's daylight so the light is off, and often when someone goes in there after dark they don't want a shower and I don't want the fan to start whirring.
So (failing some direct link from the fan to the shower mixer) humidistats seem the best solution. But from what I've read from the archives they can be a pain because they can get triggered by changing outside atmospherics. Because it seems that this is partly caused by outside air blowing in through the fan I'm thinking of having the fan controlled by an separate humidistat which I would mount on the wall close to the shower area. This one would probably do the job: http://xsls.com/?739
I'm planning on getting a 6" fan because it's a pretty big bathroom (5m x 2.5m x 2.3m). I was thinking of vent-axia's basic Silhouette 150X (no timer, no built-in humidistat).
http://www.vent-axia.com/awwebstore/products/domestic/silhouette.asp
I would connect this to be controlled by the external humidistat (which has its own overrun timer to prevent cycling). I would also like to add a 'three-way' switch which I could use to turn the thing off completely when I never want it on, to set it to humidistat control (which is where I would normally leave it) or to have it permanently on (for situations when the humidistat was not telling it to be on, but when I want it on anyway).
Two questions:
1. Does anyone have any idea where I could get a suitable switch (ideally one which would serve to isolate the fan for servicing as well, although if I had to have a separate FCU that would be OK).
2. How would I actually go about wiring this up?
Alternatively if anyone knows a ready-made fan with this level of control which doesn't work off a switched live from the lighting I'd love to know about it.
Many thanks,
Martin
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On 29 Sep 2003 15:56:04 -0700, martin snipped-for-privacy@hotmail.com (Martin Pentreath) wrote:

If it's a mixer shower, how about putting a thermostatic switch on the hot feed pipe to the tap (near the tap so hot flow to other taps doesn't trigger it). This would swich on when hot water is flowing into the bath or shower. Use this switch to control a fan that has a run-on timer, and that might be an elegant solution to the problem of determining when the shower needs to be on. An adjustable capillary thermostat like RS components (http://rswww.com ) 250-6106 would probably do the trick, and allow for tweaking to find the optimum trigger temperature. You could simply cable-tie the bulb to the pipe.
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Software problems now fixed, sorry about that.
I like the thermostat-on-pipe idea, seems to be the ideal way to control an extractor for a shower, why doesn't anyone make a fan with that as an option?
My one concern is the electrical safety. The only wiring I've done is a bit of lighting and ring mains and I'm not up to speed on how to wire control stuff like this. How would you ensure that you couldn't get 240v going down the wire to the thermostat and electrifying the bath?
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On 30 Sep 2003 12:35:49 -0700, martin snipped-for-privacy@hotmail.com (Martin Pentreath) wrote:

Probably because of the hassle of running the wiring, and the fact that you may need to experiment with the trip temperature to get reliable operation.

Make sure the bath pipe and thermostat bulb are securely earthed, and the feed to the fan is sensibly fused (1A ought to be be more than enough ).
The thermostat will probably already have good insulation between the contacts and the bulb anyway, just make sure water can't get anywhere near it - ideally inside a sealed plastic box. If you're really worried, a thin plastic insulating sleeve over the stat bulb would probably not impair thermal contact too much if the bulb is in contact with the pipe over its full length.
Wire it just like you would a fan that was switched by the light, only replace the stat with the lightswitch. The stat has changeover contacts, so you need to use the contacts that are closed when hot.
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