fan control

[Steve]

Just thinking about when I move house I want to rent the old house out, and would like some automation on the bathroom fan to prevent mould etc. The problem is the fan is a high pressure one so quite loud, so only want it to operate when someone uses the shower (not every time someone uses the John in the middle of the night to wake everyone up). There is an opening window for the toilet and bath.

At present there is just a retractable "push" switch mounted high on the wall (think it is outside of zones) under the fan. I know this probably doesn't meet wiring regs or building regs for ventilation either!

I was looking at flow switches on ebay. And some seem to only need clamping onto the pipe. Are these any good? Would I need a relay to power the fan?

Something like this. I understand it can only switch 15 watts but can handle the voltage. So would I just feed this with 230v and use it to switch a contactor? The fan is 13 watts so could run direct but is that wise with a motor load on a reed switch?

 

[AndyPRK]

Use a humidity sensor. Will work much better after the shower to clear the room.

Fit one now to treat yourself and adjust it.

 

[Steve]

Use a humidity sensor. Will work much better after the shower to clear the room.

Fit one now to treat yourself and adjust it.

Should have added, the fan has a fixed 20 minute timer (hence the push switch - push to turn on then it runs for 20 mins automatically)
This is the fan:
http://www.tlc-direct.co.uk/Products/XPPDX100T.html

 

[EFLImpudence]

There is an opening window for the toilet.

 

[Steve]

There is an opening window for the toilet.

Just re-read that and it does sound a bit wrong. Don't worry though, the window is over a public pavement, not my garden!

 

[EFLImpudence]

 

[bernardgreen]

. And some seem to only need clamping onto the pipe. Are these any good? Would I need a relay to power the fan?

The one you linked to like most replaces a section of the pipe and has a magnet inside the pipe which is lifted by the water flowing upwards.

A clamp on bi metal thermal switch that closes when the pipe temperature goes above 25 °C fitted to the hot supply pipe can be effective.

But as mentioned a good quality humidity sensor is probably the best option.

 

[AlanE]

If the shower is of the type where water flows down in the 15mm pipe to the mixer unit and then via a flexible hose to the head then the ebay switch is not suitable.

 

[Steve]

If the shower is of the type where water flows down in the 15mm pipe to the mixer unit and then via a flexible hose to the head then the ebay switch is not suitable.

And if the water flows UP? Which bit of this scenario means I cannot use it?

 

[AndyPRK]

It's important the fan runs after the shower not just during.
I guess your 20 min timer would cope with this otherwise the effectivness would be (in reverse order)

1. Flow control. Would detect when the shower was on (if it was suitable and broke into the pipe.

2. A pipe stat on the hot pipe. Would be some overrun as the stat cooled from 50oC to 25

3. Humidity sensor would operate on real conditions including bath but admit they can be a pain to adjust.