$75 · Cast Iron Heat Exchanger - General Fitting 102-F

This cast iron beast comes from a time before tankless water heaters were trendy. Don't know much about it. Probably at least 60 years old, built in Rhode Island, USA when things were meant to last, it was most recently used as a part of a cooling system and may still contain a little antifreeze. Light a fire under it and have a heater for an off-the-grid hot tub? I don't know.