What is the maximum size of threaded fittings that can be used without special approval?

The correct answer indicates that the maximum size of threaded fittings that can be used without special approval is 4 inches. In HVAC systems, adherence to codes and regulations is crucial for safety and efficiency. The limitation on fitting sizes helps ensure that the installations can be managed within standard practices.

Larger fittings often require special approval due to the increased complexity in their design, the potential for higher pressures, and the need for specialized materials or installation techniques that may not be covered under standard practices. Thus, installation of fittings larger than 4 inches would typically necessitate additional scrutiny to ensure adherence to safety standards and performance requirements. Understanding these regulations is key for professionals in the HVAC field to ensure compliance and avoid costly mistakes during installations.