Secondary Author(s)

Withers Jr., Charles

Report Number




Air Flow; Buildings


A recent study of small commercial buildings in central Florida found that uncontrolled air flow -- including duct leakage, return air imbalance, and exhaust air/make-up air imbalance -- is widespread. Of 70 buildings studied, only 1 was identified as having no significant uncontrolled air flow. The causes of uncontrolled air flow include failure of design, poor workmanship, O&M problems, HVAC commissioning failures, materials degradation, and building retrofits. This study also found that the consequences of uncontrolled air flow are often quite severe and varied -- including high utility bills, occupant thermal discomfort, high humidity, mold and mildew growth, moisture damage to building materials, transport of pollutants to the occupied space, and backdrafting of combustion equipment. The characteristics and causes of uncontrolled air flow have been largely unknown or misunderstood until recently, and diagnostic tools and methodologies for uncovering uncontrolled air flow have been largely unavailable. Standard methods of ensuring balanced air flows often fail because of measurement errors and flawed assumptions of test methodology. This paper introduces the reader to the nature and magnitude of UAF problems in commercial buildings, presents air flow management standards, and presents diagnostic tools and methods.

Date Published



Reference Publication: Cummings, J. B. and C.R. Withers, "Identifying Air Flow Failure Modes in Small Commercial Buildings: Tools and Methodologies for Building Commissioning Diagnostics." Fifth National Conference on Building Commissioning Proceedings, Huntington Beach, CA. April 1997.

Local Subjects

Buildings - Air Flow


FSEC Energy Research Center® Collection



Rights Statement

In Copyright