Automate humidity sensor and fan

Today my bathroom and toilet both have a manual system in place, where the light switch also starts a humidity fan. If i want to automate the light, I will also have to automate the fan (otherwise it’s always on).

Which humidity sensors and smart switch (for the fan) do other people use?

I use two Xiaomi Aqara humidity sensors, one in bathroom and one in e.g. the study. If difference between the two is bigger than 7% start fan, if lower than 5% stop it again (or in my case high and medium setting on central ventilation Itho). The Xiaomi sensors are cheap on Chinese sites. And they work accurate with great Zigbee reception.

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My setup for this is an Aeotec Multisensor 6 (permanent powered) which I use both for motion and humidity, plus a Fibaro double switch which controls the light and fan.
Once someone starts the shower, the humidity level jumps up quickly.
The fan will stop after either the humidity level drops close to before the shower, or after certain time no motion detected since I don’t want to run the fan forever.

@tlangelaar setup is interesting, I shall tie up the bathroom sensor with another one outside bathroom, too.

I have installed a Xiaomi Humidity sensor in the bathroom that triggers a flow that puts on the ventilation with a KUKA on/off.

In combination with the app ‘countdown’ the ventilation stays on when the humidity is above 70%, evertime the humidity changes and it’s still above 70% the countdown will expand the ‘on-time’ with 5 minutes. Works great.

Could you share your flows? I’m probably setting up the same system soon.

Sure. They’re in Dutch, ask if something is not clear enough. The flow have been created with the Web app (, screens come from preview Android app.

The triggers (when) are based on humidity changes of the bathroom Xiaomi sensor.
The conditions (and) use a Homey logic card to compare the bathroom humidity (dragged from trigger card) with the humidity from my study (dragged from tags dropdown above in flow editor) and using inline calculations with double accolades. The second condition might differ for you, I’m using a three position controlled central ventilation system).
The action (then) triggers another low that simply changes the ventilation setting. Thus way can reuse it and invite some night specific lower ventilation to reduce noise / power consumption.


Thanks, that’s a very interesting approach! I’d really like to see @danone his flows as well, if he’s willing to share. I currently have only a Multisensor 6 laying around…

Long story short, some 6-7 months ago I gave up Homey due to endless z-wave problems. Now I hear all good and in the process of setting Homey back :grinning:

I have all the old flows saved as screenshots and once I get home (end of this week), I shall share this particular one here. Thanks for your patience!

@tlangelaar Nice logic, thanks for sharing!

Thanks in advance, @danone!

Hi @tlangelaar, would you mind sharing how you’ve hooked up your itho perilex ventilation to Homey?

Yes I want to know also

I think via a Fibaro or similar double switch attached to the Itho power leads. I know i saw a scheme about that somewhere…

Found it:

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Thx, @tlangelaar!
I was looking for the same, so your post helped me a lot!

Do you still use the same numbers in your equations? So a difference of 9% humidity for turning the ventilation of and 7% for turning the ventilation off?

Looking for the most optimal values for our wet Dutch climate… :slight_smile:

I now have higher than +20 for detecting raised humidity and lower then +10 to go back to normal.

Great, thx. I’ll try that too!