As an expert in the field of HVAC systems, I am often asked about acceptable duct leakage rates. This is an important topic to understand, as duct leakage can have a significant impact on the overall performance and efficiency of a system. In this article, I will explain what an acceptable duct leakage rate is and how it is determined. The recommended maximum air leak rates from the system are found in the ASHRAE2 Manual, with a range between 1% and 5% of the system's total designed airflow at operating pressure. This means that for every 100 cubic feet of air flowing through the system, only 1-5 cubic feet should be leaking out.
This may seem like a small amount, but even a small percentage of leakage can result in significant energy loss and decreased performance. Both SMACNA and NEBB recommend using the leak class to specify allowed leaks. The leak class is determined by the surface area of the system, the required test pressure, and the specified leak class. This information is used to calculate the allowable leaks for a specific system. It is important to note that while “low pressure” ducts can represent a large part of the system and tend to leak, few construction guidelines or specifications require testing these ducts. This means that even though these ducts may be responsible for a significant portion of the air leakage, they often go unchecked. This is in contrast to industrial methods for evaluating pipeline leaks, which are based on pipeline pressurization tests and focus on “high pressure” pipelines.
These methods are more commonly used because high pressure pipelines are typically responsible for transporting hazardous materials and any leaks can have serious consequences.
