Which material is not acceptable for gas piping in water heater installations?

Plastic is not an acceptable material for gas piping in water heater installations due to safety and regulatory concerns. Gas piping must be constructed from materials that can withstand the pressures and temperatures associated with natural gas or propane, and plastic does not meet the necessary durability and compatibility requirements for these applications.

Gas lines must also be able to prevent leaks, and while some types of plastic can be used in certain applications for gas, it is generally not approved for use in high-pressure situations or where the gas line may be subjected to extreme conditions, such as in water heater installations.

In contrast, materials such as galvanized steel, black iron, and copper can effectively handle the demands of gas supply due to their strength, durability, and compliance with industry standards. These materials are commonly used and accepted in both residential and commercial gas installations.