Final answer:
When converting a furnace from natural gas to LP, the orifice size must be changed to account for the difference in gas type, ensuring safe and efficient operation. Option B is correct.
Step-by-step explanation:
When changing a furnace from natural gas to LP (liquefied petroleum gas), one important component that needs to be changed is the orifice size. Natural gas and LP gas operate at different pressures and have different calorific values, which means the orifices need to match the type of gas being used for the furnace to operate safely and efficiently.
The inducer fan does not usually need to be changed, as its function is to ensure the removal of flue gases rather than mixing fuel with air. The flame sensor and thermocouple are safety devices that detect whether the burner has lit or if the pilot light is on, and are not typically associated with the type of gas being used.
However, some adjustments may be required when switching from natural gas to LP, and an HVAC professional should be consulted to perform the conversion to ensure all components are properly adjusted or replaced.