By Gary Mann
Generally, Cymap does not add allowances by default, reference the following document:
BSRIA Design Checks for HVAC - A quality control. 8. Avoid unnecessary use of margins.
In Ducting, Cymap defaults to the Industry Accepted Leakage allowance factors so that testing of low-Pressure Duct systems is not required, because the calculation has included a factor based on the total surface area of the duct installation.
See below. 100% means that you want to allow for the worst duct fitters and site conditions available.
Setting this to zero percent implies that you can guarantee that no leakage will occur e.g. use of a factory fitted double seal made of EPDM rubber which requires no further sealing e.g. (Lindab Safe). Below is an extract from the Cymap context sensitive Help Feature (F1) detailing the calculation indices used. Setting this to zero will also allow comparison with manual calculations.