What is the maximum angle from vertical allowed for a vertical vent before it is considered horizontal?

The maximum angle from vertical allowed for a vertical vent before it is considered horizontal is 45 degrees. When a vent pipe departs from the vertical position, maintaining its effectiveness requires adherence to certain guidelines. At an angle greater than 45 degrees, the vent function can be compromised, leading to potential issues such as reduced airflow, accumulation of moisture, or even blockage. By defining the cutoff at 45 degrees, plumbing codes ensure that vents retain their ability to function properly while allowing for some flexibility in installation. This balance prevents complications that would arise from positioning the vent at steeper angles that might hinder drainage performance and overall venting efficiency.