Controlling a bathroom extractor fan

[imamartian]

I want to install a bathroom extractor. And i want it to come on only when the shower starts, and go off X number of minutes after the showers goes off.

I heard of fans triggered by infra red, and by the bathroom light going on... and by a flow switch on the feed to the shower - which is what i think would be best for me...

So my questions... firstly, are there any alternatives? and secondly, do i buy an extractor fan kit, and then the flow switch separately? and finally, is it easy to wire up a fan kit and a flow switch?

Thanks in advance people....

 

[bernardgreen]

If it is a shower fed with hot water then a thermostat that closes on rise in temperature will do the job if it fitted to the hot supply pipe. When the shower is turned off the time for the pipe to cool down will keep the fan running.

 

[imamartian]

If it is a shower fed with hot water then a thermostat that closes on rise in temperature will do the job if it fitted to the hot supply pipe. When the shower is turned off the time for the pipe to cool down will keep the fan running.

yeah it's fed from a combi boiler.... never heard of a thermostat control...? thanks i'll google it !!

 

[imamartian]

What about PIR? or flow switch? what are the norms?

 

[Spark123]

The norm is to have it come on with the light, how about a fan light with a pull cord outside the shower cubicle etc?
Flow switch may be viable, not sure how effective a temp switch would be. A PIR would work too.

 

[flameport]

The usual options:
Switched with the light - fan starts when light is on. Cheap and easy to do. Disadvantage being that in the daytime, people may not use the light and the fan won't therefore be used either.
PIR sensor - fan starts when someone enters the room. Disadvantage is that the fan will work every time, probably not what you want at 3am.

The more unusual options:
Flow switch, so that fan starts when water is used. Could be for shower only, or include toilet, basin etc. Probably the best option, but more expensive and requires some plumbing work.
Triggered by the electrical circuit for an electric shower. This involves several other components and is also expensive than other options, plus is no use if you aren't using the shower or have a non-electric one.

The useless options:
Humidity sensor, where the fan starts once humidity in the room reaches a certain amount. The problem here is that humidity varies throughout the year anyway and the sensor will require adjustment often. Depending on the fan and where it is located, they can start unexpectedly when it rains, or if the temperature falls.
Separate switch - people most likely won't remember to use it, or will leave the fan on all the time unless a retractive switch is used, and even then you might get silly persons wrenching the cord from the ceiling believing the switch is broken when pulling it again doesn't turn the fan off.

 

[Lectrician]

We used to fit flow switches in commercial installs.

These days it is always humidistats.

The Vent Axia Ambient Response ones are very good - Very sensitive, but with no false triggering.

They usually operate with in a minute of starting a shower, and run until the steam has gone.

I suppose ideally you would use a flow switch and a humidistat - The flow switch to start the fan, and the humidistat to run it on once the shower is off.

 

[Peet]

I found the humidity sensing ones to play up after a while. They draw air past the sensor to work and when dust etc has built up around it and then gets damp it didn't shut off for ages until the sensor dried out.

+1 for Bernard's thermostat. Type 'pipe thermostat' into google and be wary of which way round they work and what range they have.

Plus it also means that if the shower is just used to rinse something with cold water the fan doesn't run.

 

[Taylortwocities]

Plus it also means that if the shower is just used to rinse something with cold water the fan doesn't run.

Fine, it won't be steamy then. We are assuming the sole purpose of the fan is to rid the room of humid air.

If there is a WC there I'd like a fan to rid the room of last night's curry gas too. That's why a timer fan from the light is more usual.

 

[Peet]

That's true TTC. It sounds like you've got bigger problems there, that calls for intrinsically safe equipment and anti-static pyjamas

 

[ban-all-sheds]

Disadvantage being that in the daytime, people may not use the light and the fan won't therefore be used either.

Disadvantage #2 - people go into the room when it's dark just to wash hands or clean teeth, and the fan ends up running.

If there is a WC there I'd like a fan to rid the room of last night's curry gas too. That's why a timer fan from the light is more usual.

But what if you don't need to turn on the light when having a....?

 

[seasickstevie]

It's a wonder some manufacturer hasn't come up with an odor detector for that very purpose.
I'm sure one of the Dragons would put up a few grand at least.

 

[ban-all-sheds]

I'm 99.99% certain that the chemical signature detectors that the explosive detector machines at airports use could be reprogrammed to recognise the smell.

Or (cheaper) you could have a simple 555-type timer circuit triggered by a pressure switch on the seat. Remain in place for more than x seconds and the fan starts.

 

[bernardgreen]

The sensor used in a standard methane detector as used by sewer maintainance workers should do the job.

No hang on. There is a problem, methane is only one of several gases produced. Some of the gases produced are heavier than air and will remain in the pan or, if more than a pan full, will flow over the rim and onto the floor. Other gases are lighter than air and will make their way out of the pan and up to the ceiling, that is assuming the buttocks to pan seal is not a gas tight seal. So depending what was digested to produce the gases two gas sensors may be needed and maybe two points of extraction of contaminated air.

 

[ldoodle]

The usual options:
Switched with the light - fan starts when light is on. Cheap and easy to do. Disadvantage being that in the daytime, people may not use the light and the fan won't therefore be used either.
PIR sensor - fan starts when someone enters the room. Disadvantage is that the fan will work every time, probably not what you want at 3am.

Could you not add to this list;

Put the fan on a seperate pull chord. Fan comes on when pull chord is pulled, fan goes off when pull chord is pulled again.

Do the jiggery pokery (supply, earth, neutral, switch live) in an accessible 4 way junction box (between the light fixing and pull chord so the junction box imitates a normal light fixing), which considering most bathrooms are upstairs a junction box would be accessible from the loft. Or even a chocbox just before the pull chord if the loft is converted/finished.