"Mikepier" wrote
The T-stat is on the second floor of a 3 story bldg. It is about 8 1/2
feet high on the wall, you need a ladder to get to it.
There is one big radiator on the first floor hallway.

That 8 1/2' mark may be a 2 degree difference, even more depending on the
path of convection. With one radiator on the bottom floor, hot air is
rising and it may be following the path right past the T-stat. Cooler air
is at the stair tread level going in the opposite direction. Take a
candle and watch the flame. When I have the wood burning stove going in the
downstairs family room, there is quite a difference in air flow in the
stairwell in the hallway.

If you leave the T-stat at that height, forget the temperature, use the
numbers as a guide to what you want to have inside the apartments. #78 on
the indicator may equal 70 degrees in the rooms.

In any case, I doubt you'll ever had every tenant happy with the temperature
at all times. I can't even do that at home iwht just the two of us.