But when you go over there, they have food busting out of the refrigerator or the thermostat turned all the way up freezing all of the food. 

Each tenant has their own thermostat in the office/apartment. 

I personally keep my thermostat at 67, but in the middle of the winter here, it’s not uncommon to see someone with their door open to cool the place down.

High speed internet, nest thermostat, ring doorbell, etc.  

@Guevara MikeNothing wrong with being nice given this is your first rental and close proximity to you.You could offer to put in a wifi thermostat if she signs a new one year lease.

It’s only been a week and the thermostat has been reading near and over 90 degrees.

If you're the only one charging for gas on top of the rent, then I wouldn't consider it.Unlike water, and if you control the thermostat as I do at my rentals, unless the tenants purposely leave the windows open on cold days to spite you, you do have some control over gas usage.

He could also need access to your wifi for smart home features like keypad door locks, thermostats, lighting, etc.  

You'd need to set the thermostat for the central heat in a common area so that the baseboard heat doesn't effect it, but otherwise I don't see why you couldn't use the baseboard heat to bring each unit up a few degrees to the tenant's liking.

I am getting ready to rent my duplex in an owner/occupy situation, and I'd like to put in a smart thermostat for my rental unit.