Which type of furnace uses combustion to generate heat?

The gas or oil-fired furnace is the correct choice because it relies on the combustion of either natural gas or oil to produce heat. In this type of furnace, fuel is burned in a combustion chamber, and the heat generated is then transferred to the air or water used for heating the living space. This process involves two key components: an ignition source to initiate combustion and a heat exchanger to facilitate the transfer of heat while ensuring that combustion gases are safely vented outside.

Electric furnaces, in contrast, do not use combustion but instead rely on electric heating elements to generate warmth. Heat pumps function differently as they transfer heat rather than generate it through combustion, often utilizing refrigerants and the principles of thermodynamics to move heat from one place to another. Geothermal furnaces draw on the stable temperatures found in the earth's crust and are categorized as heat pumps, relying on the earth's natural heat rather than combustion. Thus, gas or oil-fired furnaces stand out as the types that explicitly utilize combustion to create heat.