What is the nominal size of a standard 90-degree elbow?

The nominal size of a standard 90-degree elbow is defined by the diameter of the pipe with which it is intended to connect. In the HVAC industry, 4-inch elbows are a common size used in many ductwork applications. This size allows for good airflow and adaptability in various installations, making it a standard choice for most residential and commercial systems.

Using a 4-inch elbow ensures compatibility with other duct fittings and components typically used in a system, promoting efficient airflow and minimizing pressure loss caused by bends in the ductwork. Additionally, the 4-inch measurement aligns with industry standards for ventilation, heating, and cooling systems.

The other options may represent nominal sizes of elbows found in HVAC applications, but they do not correspond to the standard, commonly used size like the 4-inch elbow does. This standardization helps technicians, engineers, and installers to work more efficiently, ensuring that all components fit together seamlessly within the system.