Bathroom extractor/ humidity sensor

[Nick Barton-Wells]

Hi all

I am wondering on the best method to trigger an extractor far in several ensuits.

I was looking at using the comfort air sensors but that seems like a bit of overkill for each ensuit?  

I have seen people comment on using flow switches. 

https://cpc.farnell.com/te-connectivity/fs-10/flow-switch-15mm-05l-min/dp/SN36477?mckv=sshopping_dm|pcrid|490691434481|kword||match||plid||slid||product|SN36477|pgrid|47130025876|ptaid|pla-1952127139673|&CMP=KNC-GUK-CPC-SHOPPING-946695261-47130025876-SN36477&s_kwcid=AL!5616!3!490691434481!!!network}!1952127139673!&gad_source=4&gad_campaignid=946695261&gbraid=0AAAAAD_m6B2gVOxnNRWd2HV9sKXGYREZo&gclid=CjwKCAjwl_XBBhAUEiwAWK2hzsK54EymtnOlDOM5AtOzKARAd2V_4j20nfMDCWepc-CfumvE31FF3xoCp-gQAvD_BwE

I could use this on every hot feed to trigger the extractor fans. What do people think?

Thanks

Nick 

[Steve Joyner]

I use flow sensors (the exact ones you link to) on the shower outlets to start the fans when the shower is used, and then a timer to turn fan off.  I also have a button for manual fan start in each bathroom.

My experience:

• This solution has in general been performing well for several years - much better than no automation and relying on wife/kids top remember to start the fan !
• In my case, putting the sensor on the hot feed to the shower didn’t;t work so well, the flow switch tends to stick at on even the the shower is turned off - I]’d guess this is something do with the pressure in the pipe not blowing the switch to turn off - but could easily be an installation/positioning issue - either way moving flow sensors to the outlet side of the show valve has worked fine - and no-one ever has a cold shower so no false triggers - there is always steam with a shower.
• Without any kind pop humidity sensors I\vge ended up turning up the delay on the fan stop fairly high  - about 40mins now - to clear all the steam in the worst case.  I think it’s likely that some quicker showers need less fan time, so possibly I’m run-in the ran too long in some circumstances.  Some sort of humidity sensor too say when to turn off again might be a further optimization.
• I now have a different timer on the button for starting the fan - this is much shorter as manually triggered fan runs to clear smells only need to be about 5 mins.

Hope that helps

Steve

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[g...@camleyphotographic.com]

You could put a temperature probe on the hot pipe. When the temperature rises, then you know the tap has been turned on. 

This will avoid pipework, and likely be less expensive. 

I do something similar to warn me when the hot water is getting low and I should stop running the bath. I tend to have the last bath in the day and our 300L tank sometimes runs out of hot water.

G

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[Techdoctor]

The way I do it is if the bathroom lights are on for longer than 3 minutes then the extractor fan goes on, and when the lights go off 5 minutes later the extractor fan goes off. Since all the lights in my bathrtoom are controlled by Loxone its quite easy to do, so it doesn't matter which lights are switched on. I have a bathroom mirror light, controlled via a loxone module and the Loxone Tree RGBW spots. 

I have also done something similar for a client who has a Loxone system, but since his house has 7 areas that needed extractor fans going the Loxone route was going to be expensive for him. So I used Shelly modules, all controlled via Loxone. That way he only needs the one app.

[Nick Barton-Wells]

Thanks all.
This is all part of a very large refurb i am doing. I hadnt through of using the motion sensors.  I will look at the flow switch seeing as i have the 1-wire extension and will be able to then have a fall back option if required using motion.

Maybe i should post my house plan up for feedback. Thanks again all

[Simon Still]

If you want to do it properly then it's got to be a humidity sensor.  you dont really want fans running longer than necessary (the noise is annoying) or stopping before they've sufficiently dried the air in the room.

Does it have to be air?  Can it be wired?  I've got analogue temp/humidity sensors that Loxone used to sell but you could make your own or use 1-wire sensors. 

I've got them set up with a high/low threshold relative to a sensor thats not in a bathroom  (because otherwise you get edge cases when the ambient weather is very humid and the fans never switch off.  

[Nick Barton-Wells]

Yes, my original plan was to use the Room Comfort Sensor Air which records both temp and humidity, but for £10 more, i could get the Touch Tree which includes buttons for other functions.  
Just seems like overkill and expensive way to get humidity reading from some rooms.  5 rooms needing humidity to be recorded so to manage the extractor fan is expensive if i go down the loxone product route.

This is why i was looking for alternatives.  Does anyone know a cheaper option, maybe a 1-wire extension or analogue sensor i could use to get humidity of a room? 

[Nick Barton-Wells]

I could use a Shelly HT device:
https://www.shelly.com/products/shelly-h-t-white?variant=56273493786973

Would rather a wall mounted device than a device like this

[Jonathan Dixon]

Recent project we came to same conclusion and put some touch tree (classic) into bathrooms to act as humidity sensor and bonus buttons. (There's a more conventional light switch in the conventional location).

Also currently exploring some basic AliExpress modbus humidity sensors but they're ugly if not boxed up some how. (In my caer will be utility areas, or in a vented din panel so not an issue)

Agree there's a real gap in the Loxone portfolio here. A cost effective way to supplement conventional switches as everyone wants in period UK properties would work well, maybe something tethered to the same nano io back box as the light switch, akin to a heatmiser thimble sensor. 

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[Deac99]

Not to be argumentative but rather to offer a funny story along these lines.  I used to live in Iowa (USA) which is an extremely unpleasant  state weather wise (There is a reason they call it the fly-over state 100+F and 100% RH in the summer, and -40F in the winter).  I found a switch for the light that had a built in RH sensor that would trigger the fan which was adjustable for the RH for when the fan would come on.

I knew the RH in Iowa was unbearable in the summer but did not know it was above 95% frequently such that the fan ran day and night for weeks.  I removed the switch and replaced it with the original 2 switches for the light and the fan.

We did have AC in the house but only in a couple rooms.  - Yes, it was a miserable few years while we lived there.  :)

[Paul Watkin]

Hi Nick,

Rather than just jumping straight to a technical solution and without being flippant I am wondering what the problem is that needs fixing here i.e. why do you want to automate the fans in the first place?

If you are using decentralised ventilation (i.e not doing MVHR etc) there is very little benefit and a lot of cost in trying to control several individual fans via Loxone in my opinion.

By far the simplest approach for ventilation would be something like the Envirovent ECO dMEV+HT-LC Centrifugal Extractor Fan with Humidistat & Timer (assuming UK based) - it will sit there completely happily and almost silently doing its own thing - easy to set up and just works - just supply it permanent mains via T&E and thats it. Retail is about £100 inc vat, 

Slightly more complicated would be to use completely dumb fans wired back to a Loxone relay and control via simple logic such that if bathroom lights (could be triggered via light switch or presence sensor) go on for longer than x time the fan will run on for y - you can also then add things like not running the fan with house in night mode etc - drawback is that simple fans tend to be noisy as they are cheap. Vent Axia do some very quiet dumb fans but they were about £80 a throw. 

I have done this in the past mainly for downstairs WC's in customer's houses where the WC is in the middle of the house and they don't necessrily want the noise of a fan intruding. £30 for Fan, £40 for a relay channel assuming using Loxone Relay Extension, plus sparks time to run in a cable to Loxone panel from each fan plus programming, plus panel space etc, I suspect about £200+ all in? But on the upside you can also run the mirror demister pad in parallel.

Also bare in mind that you will still need to fit local isolation of each fan on the outside of bathrooms for maintainance even if you go for a fancy control mechanism via Loxone.

Sensing waterflow in pipework or using humidity sensors to me is a last resort as the solution cost massively outweighs the gains - without further insight into your use case, maybe you live near the sea with a prevailing onshore breeze?,  I would say there is unlikely to be any need to go further than the above apart from the "because I can" approach

Personally we have designed MVHR into our new build and that will be controlled to a degree via Loxone but only so far as a boost mode override to allow purge ventilation on a schedule, if the house overheats, or if the Radon sensors trigger - it will also cut out if the smoke alarms or misting system (fancy low water usage sprinkler system as house is a timber frame) are triggered - otherwise it will just carry on doing what it does without any other input.

Paul

On Tuesday, 3 June 2025 at 07:55:18 UTC+1 nick....@gmail.com wrote:

[Simon Still]

My first thought was 'why is OP fitting extractor fans' as they're a) noisy b) draughty  c) inefficient (dumping heated air from the house) 

Looking for something the other day came across these single room heat exchange units - https://bpcventilation.com/collections/heat-recovery-fans/products/bsk-zephyr-single-room-heat-recovery-unit  which looked pretty cost effective.  

[Techdoctor]

I have a  Vent-Axia 446658B fan , and you can't hear them, so fans needn't be noisy. I also installed seven of them in a client's house, and had to take the covers off to prove to them that they where actually working they are that quiet.  At least by using shelly modules with power monitoring you can actually see that they are working.  As for drafty not in my experience. Most decent fans these days have some form of back draft preventer built in or as a clip on device. Also the exterior vent can also have shuttering, which will open when the fan is running, the ones I fit just work on the air pressure moving past them, so when the fan stops the shutters close. Very easy and requires no extra control or electrics. 

So your arguments for a and b in my opinion are not valid. C on the other hand can be seen as a problem depeding on where you live.

[Nick Barton-Wells]

I think i have over thought this somewhat.  Yes i can manage the extraction of damp air from an ensuite.  But do i need to do it with Loxone.

I have 5 en-suite, all have UFH which will be managed via Loxone.  I was hoping it would be simple and cost effective to manage the extraction of air as well.  
The  Vent-Axia 446658B fan or Envirovent ECO dMEV+HT-LC Centrifugal Extractor Fan look like. good solution.  

Thanks all very much for your input

[Paul Watkin]

Hi Nick,

One thing you might want to consider is possibly having Loxone override the heating schedule to put the heating on for a bit based on humdity to "dry" the ensuite out - you could use the humidity sensor in the light switch to control a heating boost for that zone therefore possibly more quickly reducing moisture - given the UFH is managed by Loxone and you already have a light switch in the room it is free to do apart from your time to program it.

I intend to have a play with something along these lines once we get into the house, I would be interested to know if anyone else has done anything similar previously and if it worked?