What must coated copper tubing have installed at the tank when used underground?

When coated copper tubing is used underground in oil fuel systems, it is essential to have an Oil Safety Valve or Pressure Relief Valve (PRV) installed at the tank. This requirement is crucial for safety reasons. The Oil Safety Valve or PRV is designed to prevent excessive pressure buildup in the system, which could lead to leaks or catastrophic failures. This valve acts as a safeguard to ensure that any pressure exceeding safe limits is released, thereby protecting both the tank and the surrounding environment from potential hazards.

In the context of underground installations, where access to the system for maintenance or monitoring is limited, the presence of an Oil Safety Valve or PRV becomes even more critical. It ensures that the oil heating system operates safely and effectively without requiring constant supervision. Therefore, the correct answer reflects a mandatory safety component necessary for the integrity of the installation.