Extractor Fan Wiring

[aberdeen]

I've bought an extractor fan for a downstairs utility room / WC. The room is entirely internal with no external walls though I am able to run the vent pipe through an adjacent false ceiling so that bits OK. The fan has a standard run-on timer that would be connected via the lighting circuit but I would also like to wire in a way to have the fan on permanently on a low speed with a fan speed controller so that when the tumble dyer is on (its a condensing model) any excess moisture can be extracted by the fan running at a low speed. Question is - is this feasible and if so how ? TIA

[Lobster]

Best and much easier solution IMHO would be to return the fan and buy a replacement model with a built-in humidistat, that will deal with any excess moisture as necessary as opposed to running continuously.

hth David

[Michael Chare]

In theory you could use a current relay in conjunction with a delay off switch/relay. I use this combination to turn our cooker hood on whenever the electric hob is used.

[David Hansen]

On Thu, 13 May 2010 13:42:59 -0700 (PDT) someone who may be aberdeen wrote this:-

It is entirely feasible. The best thing to do is buy a fan with this built in. It normally runs at low speed, high speed can be activated by a pull cord or external signal from lights, humidistat or motion detector.

Alternatively one just turned on by a humidistat may be a better solution.

[Tim Lamb]

In message , David Hansen writes

Has anyone any direct experience of using a *humidistat* in a domestic environment?

I have fitted one in a bathroom to bring in a boost setting on a heat recovery extract system and have yet to discover if it is effective.

The flat is currently unoccupied and hence unheated. The initial set up appeared to show the trigger point as around 60% rh and the stat was set up to 70% to avoid nuisance tripping. When I checked recently, the trigger and hence the humidity level had moved down to around 50%.

Obviously weather/temperature changes hugely affect rh and I am worried in case a situation can arise where the fan is trying to dry out the whole of Hertfordshire and hence not switch off:-(

regards

[Calvin Sambrook]

I have a humidistat in our new bathroom which controls a dehumidifier built under a seat and drawing ducted air from a high level. It works very well set to just under 75%. If the room gets steamy when the shower is in use for a long time it turns the dehumidifier on, generally just about when I'm getting out of the shower.

The one we have is basically a strip of material which stretches when damp connected to a microswitch, very crude but effective although it has quite a lot of hysteresis.

[John Rumm]

Yes I have done a few of them, in a bath / shower rooms. They seem to work very well.

They normally kick in shortly after the shower started, and run for 20 mins or so after bringing the moisture level back down. You sometimes need to tweak the trigger level a bit as the seasons change or if you have a really wet damp day.

[John Rumm]

I would expect a dual speed fan with built in humidistat and external run on timer would be the simplest combination to get all the capabilities you desire.

[Tim Lamb]

In message , Calvin Sambrook writes

OK both.

I am relieved that I may get away with penny pinching and not buying the temperature compensated version.

Follow up on the *baffle box* soon.

regards