Hey @Casper… I posted an update quite a while ago 
Go to my post and notice the 4th image which is a wiring diagram, it shows the optional temperature sensor… Then go to the Arduino code on GitHub and grab the new version. Lastly, don’t forget to change the SmartThings Groovy code and replace the older Generic HTTP Device with the new version — which simply has the two extra tiles (temp/humidity) at the bottom that read from the ESP8266.
The last piece that you’d likely need to do is either try to fire the “ON” for your fan somewhere in the loop() method of the Arduino code — or the more advanced and probably configurable Smart App code in ST which can subscribe to the Device’s state. Then you can do things like change that temperature range, etc… but to be fair you can also do that in Device Type preferences/settings and then send to the loop() to now respect. Two ways to do things and I’d probably try to stick to just Device Type for ease of maint and my lack of familiarity with Smart Apps.
Enjoy and let me know how it worked out.