Duplex with one thermostat

[Kamron Lewis]

Hello, I recently purchased an up/down duplex in the Pittsburgh PA area. The unit was a SF legally converted into a duplex and currently is heated via Water Boiler with radiators through out both units. The problem is that there is only one thermostat located in the upper unit. One option is to put a lock box cover over it and designate a set temp for the winter but personally I would rather not do that as I know I would rather have control over my temp as a renter. Any advice on the best was to deal with this issue would be appreciated!

Thanks