Describe the combustion process for natural gas, propane and heating oil.

• A. The heat exchanger extracts heat from combustion products and transfers it to the heating medium; exhaust is vented through a chimney or exhaust
• B. The heat exchanger creates the fuel
• C. Combustion products are vented into the living space
• D. The fuel is never burned

Answer: (A)

The process starts when the fuel (natural gas, propane or heating oil) mixes with the right amount of air and is ignited in the burner. The chemical reaction releases heat, warming the hot combustion gases. These gases flow through a heat exchanger, where most of their heat is transferred to the heating medium (air in a furnace or water/steam in a boiler) that will be circulated through the building. The combustion byproducts are then vented outside through a chimney or dedicated exhaust so the living space stays safe and free of fumes. This sequence—fuel-air ignition, heat release, heat transfer via the heat exchanger, and outdoor venting—applies to these fuels in typical heating systems.