1 Heating/Hot wtr heater unit servicing many tenants. Solutions?

[Alex Hal]

Hi, Hopefully posting this to the right forum category.

i did an inspection today on a commercial property consisting of 2 office buildings (4 tenants in one building and 1 tenant in the other with one vacancy) and a residential unit (2 tenants).  Each building has one oil tank and one boiler.  Each tenant has their own thermostat in the office/apartment.  Since there is no way to divide the heating bill evenly, the current seller rolls the heat into the rent.  During the walk through we noticed that some tenants had there heat cranked to 80 degrees, while some kept it at a comfortable 70.   One tenant had the windows open and heat up to 74.  The cost of oil (no natural gas in the area) for the 3 buildings is approximately 9K a year.  That gets expensive and cuts into profits.  

Few questions.

1.  What is the best way to throttle the max temperature a tenant is able to heat the apartment on my dime?  i.e. up to 70 degrees is my responsibility, and after the tenant can use electric heaters.  Is such an approach legal?

3. If there is no way to throttle, how can i monitor the energy consumption from each tenant?  Maybe some sort of a meter exists that can measure how much energy is being emitted to each zone.  i am thinking it would be installed at the boiler.  The boiler on premises resembles the setup in the picture in the link.  boiler

Thanks in advance,

Alex