I have a steam boiler with a hot water return for heating my basement. There's a circulator and I would like to install a thermostat to regulate the basements heat. When the upstairs dwelling is 70 degrees the basement is around 95.

Hi Ekralc

It is not nearly as simple as just installing a thermostat... a lot of controls/valves and safeties are required to balance a system as you are suggesting.

Does the "wet return" have any radiators/baseboard on it?