I have seen one or two smart apps for fans, although I am not sure if they meet your specific needs. They one I found was this:
For what it is worth, I plan on writing a very similar app to what you describe, but even taking it a bit further. I am going to write a smart app that will let you set limits like you specified, but also look up the weather for the coming day to try to keep the temperature in a target comfort zone as long as possible and send notifications.