Duct leakage can be estimated by taking a blower door CFM50 reading with all duct registers well sealed (CFM50Closed) in addition to one with them open (CFM50Open). The difference between these measurements indicated duct leakage at 50 Pa. This can be converted to a leakage at 25 Pa as follows
LeakageCFM25 = (CFM50Open – CFM50Closed) / 1.62
This can be entered into OptiMiser by selecting “Measured (cfm25)” in the Duct Leakage control and using the cfm25 control that appears to the right.