How many 90-degree elbows are acceptable in a main vent system if vertical?

In a main vent system, the acceptable number of 90-degree elbows is limited primarily due to performance and airflow considerations. Allowing one 90-degree elbow provides a balance between maintaining effective airflow and preventing excessive resistance within the vent system.

Elbows create turbulence in the airflow, which can impede the proper functioning of venting systems. Having too many elbows can lead to an increase in back pressure, which may prevent gases from exiting efficiently. The code and best practices are designed to ensure safe and effective venting while minimizing complications related to airflow. Therefore, allowing only one 90-degree elbow in a vertical main vent ensures that the system operates efficiently and within regulatory guidelines.