Any idea's how to do this? control a humidity fan depending on outside humidity

I installed a humidity sensor in my bathroom to control the central house fan, in the bathroom.
But after tuning the threshold, it stays on too long. This is because the humidity outside is higher, because o a rainy day for example. And so inside is higher too, open windows etc.

So, does anyone have an idea how to make the threshold dynamic, depending on the outside humidity? I already installed a plugin which uses my location and gives me the humidity. I could made several conditions, but that is way too much work and effort to control. I would like to have something like if outside is 70-80, inside threshold is 75. If outside is 80-90 then inside threshold is 82. Etc. The idea is that the inside threshold much be higher when outside is higher too.

Wouldn’t outside_humidity+10% be a sensible way of doing it?


Hmm didn’t think of that, but how do you mean exactly? I mean, I need to measure the humidity in the bathroom, because of people taking a shower.

How about something like this to turn the fan off?

inside_humidity <= 75 OR inside_humidity <= outside_humidity

You have a fixed value for dry days, otherwise it shuts off when it’s the same as outside.

Tried something like that already. But on very rainy day, outside is 95% or sometimes even 100%.
So the fan will never turn off.

I need something like if outside is x more then avarage, then inside threshold will be slightly higher too.
And thus the inside threshold should be higher.

inside is always lower then outside, btw.

You should also keep in mind that the humidity inside and outside can not be compared unless the in and out temperature is the same.

In other words Outside humidity at 70% and 5 degrees centigrade is not the same as inside humidity at 70% and 21 degrees centigrade. In this example the outside air may only contain half the amount of water compared to the inside air at the same humidity.

At that point I’d probably just get another indoor humidity sensor as reference. Sounds like a pain to get a formula like that in there.

Thanks so far for all your info. Maybe a second indoor would be better indeed.

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