said by PhoenixDown:
Sorry for the confusion -- its one thermastat. The original system was built at the time of the house and my parents added baseboard heating maybe 15 years ago. We looked at separating out the apartments but it was cost prohibitive.
I always thought the first and second floors were served by steam as there are little release values that let out the steam and control the system pressure but I could be mistaken
It was originally a coal-powered system that was later converted to natural gas and finally replaced by a new (relatively speaking) natural gas boiler.
Thank You that cleared my confusion. It indeed does sound like steam now that you described it. There's not much you can do there to separate the tenant off that system . Any heat controls / learning T-Stats would affect the tenant as well as you. If you did go with something like the nest you could HOWEVER the tenant would have to be figured in to the settings.