The term heater comes from the Latin word calefactus, which derives from heater (translatable as “to warm”). When it appears as adjective, heater refers to that which heats: that is, it transfers heat to a body causing an increase in its temperature.
As a noun, heater refers to device used to heat the air. A heater, therefore, is a heating appliance.
What heaters do (also called stoves in some regions) is to generate a hot air flow from a source of hot. There are multiple types of heaters according to how they produce heat: they can work with firewood, gasoline, Coal, gas or electricity, to mention a few possibilities.
Take the case of electric heaters. These devices use the electric power to produce heat energy, being able to appeal to joule effect or to peltier effect.
The gas heaters, for their part, they have a main valve and other valves linked to each of their burners. In this way, the amount of gas that is sent to the burner by means of a knob: the greater the amount of gas, the greater the flame and the more heat released. What the knob allows is to control the level of gas that reaches the burners, thereby controlling the flame and the heat that is released.
A wood heater, meanwhile, it works from the incineration of wood. The combustion process causes the wood to reach very high temperatures, releasing heat. The smoke that is generated, in turn, is discarded so that it does not remain in the environment.