The crossword solution for the term 'Heater or Cooler' is 'RADIATOR'. A RADIATOR is a device used to transfer heat from one medium to another, either to heat or cool a space. It is typically found in heating, ventilation, and air conditioning systems. Radiators are usually made of metal and contain a liquid or gas that is heated or cooled by a heat source, such as a furnace or air conditioner. The heat is then transferred to the surrounding air or water, depending on the type of RADIATOR.