hot water heater vs vessel

hot water heater

noun
  • An apparatus, usually fuel-burning, electric or solar-powered, in which water is heated to be used directly as domestic hot water or process hot water (but not for supplying space heating, calorifiers etc, for which a boiler or furnace is used). 

vessel

noun
  • A container of liquid or other substance, such as a glass, goblet, cup, bottle, bowl, or pitcher. 

  • A craft designed for transportation through air or space. 

  • Any craft designed for transportation on water, such as a ship or boat. 

  • A tube or canal that carries fluid in an animal or plant. 

  • A person as a container of qualities or feelings. 

verb
  • To put into a vessel. 

How often have the words hot water heater and vessel occurred in a corpus of books? (source: Google Ngram Viewer )