Even Superman has kryptonite..
translation: I don't think Super Smart Fan has to incorporate EVERY scenario. RuleMachine, and the other built in tools can still do their jobs. @halfrican.ak has the quiet fan, and I wish I did, but I'd rather that rule be outside of super smart fan if I had a vote.
You do realize don't you that you can do this with Rule Machine? It will compare humidity between two devices, etc.
Yes, we do, my examples were posted above. Andy and I just thought it would be nice to have an app that would handle all the rules in a more user friendly way. I had 5 rules to do what this app can do (of course if I was better at building RM rules I may have been able to do it with less).
I get it. This is exactly why Motion Lighting came into existence. RM could do everything Motion Lighting does, but for the most complex situations would entail numerous rules.
Bruce
Little apps like this help to relieve the boredom of working from home on a super reliable system that needs no work 
Andy
First couple of tests were successful.
Manual turn on time-out worked as designed
RH of bathroom % above baseline turned on fan worked as designed.
RH of bathroom at or below % of baseline turned off fan as designed.
I meant to ask one more question..
If someone were to turn-off the fan manually while RH is still above % of baseline, how long will it take for the app to realize this and reactivate the fan?
Probably the next humidity report from the device.
Exactly that!
The fan would restart if the next humidity report is still above the threshold.
Andy
Guys
I have 'tweaked' the app a little and added ability to use 'average' of more than one baseline humidity sensor.
I thought this might be useful
New version : 1.1.0 uploaded to GitHub
Do you think it would be worth adding the same to the bathroom humidity sensor?
Does anyone have more than one in a bathroom?
Andy
I imagine someone might have a larger enough bathroom to justify a second humidity sensor, so it's not a bad idea.
I have only one humidity sensor currently, which is in the bathroom. Should I be selecting this sensor for my baseline as well or leave baseline unselected?
The app was actually designed to use two humidity sensors.
One inside the bathroom and one outside (baseline)
As it stands, I'm not sure this will work for you
Let me have a look and I can probably set a 'zero' as the baseline if a baseline is not used.
Andy
Ill just buy another sensor
Mark, I was following this for a while and then got onto other projects. My daughter just never remembers to turn the fan on, or doesn't want to, not sure which. So I'm now coming back around to this. Thinking of using either @iharyadi 's sensor for humidity or a Xiaomi together with my Ecobee for the indoor base humidity.
What switch are you using for the fan? I'm concerned about confusion between light switch and fan for guests, so a regular toggle smart switch (of which I have two spare available) may not be my first choice.
I'm using an aeotec multi-sensor 6 (USB powered) for bathroom humidity. A zooz 4 in 1 for the adjoing room "baseline" humidity. A lutron caseta switch for the fan.
I also have a lutron caseta switch for the lights in bathroom right next to it, but since everything is automated through this app or motion lighting I don't have an issue with anyone confusing the switches. Even if someone were to manually override the fan switch the app with reactivate when the humidity reports again or after the time out.
I specifically chose the casetas because the do a good job of reporting physical interaction with the switch and I'm using their products throughout the house anyway.
Beware that most/many z-wave switches are NOT rated for "Fan" loads so make sure whichever switch you choose is.
Thanks so much. Yes, the two switches I have on hand are an iDevices and an Insteon ON/OFF switch. Both rated for 1HP motors. Insteon wouldn't have been a choice for this use, but now that I have direct control, these are good quality choices. I have Castea Pro too, so micro module and pico is another thought.
Already have a Hue motion sensor in there, but it's paired to the bridge. Don't know if it's possible to use it for activity when the light is bright enough not to activate the lights. Guessing I would have to pair it directly to Hubitat.
I've got motion lighting set to turn on the switch with motion only during day/twilight/night location modes.
I have a "sleep" mode that I use when no motion has been detected in the main living areas for more than 10 minutes after 10:30 pm. During sleep mode the bathroom lights don't come on unless the door is closed and motion is detected (using RM). During sleep mode I have a "Smartplug" attached to a night light that activates with motion (so it's not on all night).
Thinking more about this and my aha moment has arrived early! 
Currently I have a Leviton 5, 10, 15, 30 push button timer which works great and everyone is used to it. For me, an Insteon 2443-222 ON/OFF micro module is the ideal choice, since I can simply attach it to the fan in the attic. It can be in a moisture-proof box, because of the Insteon dual mesh, it will still get it's signal through the power line. Their micro modules can be programmed to support either momentary contact or latching mode. So in latching mode, when a timer button is pressed, the load will be sensed by the micro moduel and will turn on the fan, turning it off when the wall timer turns off.
Using the Insteon direct driver, I'll be able to also control the fan with @cobra 's Super Smart Fan app when x%RH is above the baseline.
So simple. Thanks to both of you for making this possible.
I have almost the same setup as you with one exception...
Motion detection is done with a Lowes Irirs Motion sensor that turns on the light over the vanity. I have an Aeotech Multi-Sensor 6 USB powered in the ceiling that I use for humidity sensing and as a secondary motion sensor for the shower to keep the lights on when someone is in the shower. It's not he primary motion sensor because it would be detected in the hall and would turn the vanity light on everytime someone walked by. I plan on putting a door sensor on the door for open / close and I'm using two Lutron Caseta switches, one for the vanity light, and the other for the fan. I just ordered the Zooz 4 in 1 sensor for baseline for humidity.
I'd be interested to hear more about your setup and how you've configured your Aeotech multi-sensor 6 in it's own device settings as well as the rules you've setup to make it all work. I'm getting ready to start configuring this extensively in my home. Thanks for any input you could provide!
I actually use a zooz 4 in 1 mounted above my shower facing out so that it covers motion in both shower and rest of bathroom. I don't use the aeotec for anything other than humidity.
I have the aeotec connected via USB. I've enabled selective reporting and set it to report change in humidity of more than 2% and/or every 3 mins.
I used @Cobra Andy's app to control the lutron caseta switch that powers the fan. I've configured the app to turn on the fan it humidity is more than 2% over baseline (zooz 4 in 1) located in the adjoining Master bedroom. Also have it set to turn the fan off when humidity returns to baseline or after 20 minutes if manually turned on.
I use the stock HE driver on the Aeotec but customized the settings using @mike.maxwell basic z-wave settings tool.
For lighting I use Motion Lighting to control another caseta switch for the fan and vanity lights. I have it configured to only turn on when location mode is day/twilight/night. If mode is sleep I have a nightlight powered by a Smartplug that turns on with another motion lighting rule that only triggers during sleep mode.
I also have an RM rule that turns on fan/vanity light if Master Bath door is closed (Iris contact) while in sleep mode and motion is active, assuming that if the door is closed full lighting would be desirable even if in sleep mode.
Download the Hubitat app
