combustion vs storage heater

combustion

noun
  • A process wherein a fuel is combined with oxygen, usually at high temperature, releasing heat. 

  • A process whereby two chemicals are combined to produce heat. 

  • The act or process of burning. 

  • Violent agitation, tumult. 

storage heater

noun
  • An electrical heater which stores thermal energy during the evening or at night when electricity is available at lower cost, and releases the heat during the day as required. 

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