Run pay back analysis on each improvement you get most for the bang for the buck.Also have timers on the thermostat during off hours.

She came to me and said there was something wrong with the electric ,it was more than what the previous tenant was paying .I asked her if she used the oven , did laundry , blow dry her long hair , and kept the thermostat set to 70 degrees .  

I've changed the thermostat for upper unit but the tenant can't adjust temperature.

For that price, each unit will simply have a dial on the unit rather than a separately-wired thermostat. 

Are you allowed to regulate thermostats in a multifamily unit? 

Have them shut off hit runs to the hot areas to push more heat to the cold areas, acts like a power mans zone system, They have damper that have thermostat and work well4.

Thank you for the discussion You can always get a NEST or other thermostat which will tell you the temperature inside of your home.

@Ryan AdamsAlso just to get ahead of this - Im aware the manager should have had the heat on at a reasonable level given the time of year but have no idea where the thermostat was set.

This allows for the control of two thermostats on a single unit and air handler.

I have 12 for my building including 3 mailbox keys and a thermostat lock key.