The origin of system effect is different at fan outlet and at fan in let. At the fan outlet, for example in the case of an improperly connected outlet fitting such as an elbow, damper or duct branch, the system effect is linked to less-than-optimum non-uniform flow profiles induced by the fan at the entrance to the fitting (Figure 1). This degraded flow will create more pressure loss across the fitt ing than would be the case when measuring the fitting loss assuming uniform homogeneous flow profiles or when estimating it from standard handbooks such as the ASH RAE Handbook of Fundamentals.