I am renting a duplex built in the 1960's. The property manager told me the heat source is "radiant heat". I cannot figure what exactly this means. The duplex has a small heat control box is each room, which very much look to have originated in the 60's. There are no vents (there is wall a/c) and no radiators so I cannot figure out where the heat comes from. Did radiant heating exist in the 1960's? What else could it be?

Jamie in Nashville, TN