Which aspect is critical in the installation of fuel gas distribution systems?

Correct sizing is critical in the installation of fuel gas distribution systems because it directly impacts the system's efficiency, safety, and functionality. Properly sized gas pipes ensure that the right amount of gas flows to appliances at the correct pressure, which is essential for their efficient operation. Undersized pipes can lead to insufficient gas flow, resulting in poor performance or appliance malfunction. Conversely, oversized pipes may not provide adequate pressure drop, potentially leading to safety hazards due to gas accumulation.

Additionally, correct sizing takes into account the type of fuel gas, the distance from the gas source to the appliances, the total load of the appliances, and other factors that can affect gas flow and pressure. While the other options like cost-efficiency, color-coding, and automatic shut-off features are important considerations in the broader context of gas distribution systems, they do not have the same immediate impact on the functionality and safety of the system as proper sizing does.