I own and manage several properties with a “central thermostat” a number a years. We have locks on them, though in most cases a “resident manager” has a key to adjust if needed.
Most of them are building built in the 1950’s or before, with a central heating furnace, and heat is generated either thru a hot water, or steam system. No way it can be zoned.
A word of caution about setting the temperature to 68 to 70 or so degrees. We manage a building for a relative where the heat was set this low, and get constant complaints.
When the temperature is set, it’s the temperature around the thermostat, not the colder regions a floor above, or below, or in the back where the wind blows. We got ourselves a bunch of thermostats, and found that the temperature differences can be as much as 6 to 8 degrees.
When the temperature was set at 68 degrees on the second floor, as was the case in this building, a room on the third floor rear was at 60 degrees. The law requires 66 or above during the day, and the tenant can file a legitimate heat complaint.
What you have to do is balance the heating system, reducing heat at the warmer regions, by changing valves, or shutting off radiators, and increasing the heat at the colder regions. The would reduce temperature differences to 3 degrees or so.
We found we have the least heat compliants if the temperatures are kept at 70 degrees or above in the coldest rooms, meaning the temperature would have to be set in the 73 to 74 degree range, after the heating is balanced. Any less, we’ll get heat complaints, and sure enough, if we leave a thermometer, the temperature will be at 67 degrees or so, if the thermostat is set at 70 degrees.
As to apportioning the utilities, we have tenants agreeing to the procedure in the lease, and actual bills are provided. My dad did that for years and years with no problems.
For most of my buildings, I include the heat though, since this is the normal custom others charge in the area, and tenants prefer a fixed rent a month, and would not rent a place where the heat is separate. So we charge enough to cover the heat.