Make sure your contract states that you will be able to come into the house monthly to change the filters (and do a quick look-see for outlandish rule breaking). Our renter "didn't know" she was supposed to change the HVAC filter, and never did it in 2 years. She kept the place immaculate, we never dreamed she'd cost us so much until the unit blew up. Of course, it was winter and we had to replace it quickly. Her security deposit was not enough!