"NL" = No limit on duct length for the specified system.
"X" = Specified system is not likely to achieve the design flow. Please vary the inputs to identify a compliant system.
This tool may be used to comply with the requirements of 2015 IRC Section M1506.2 and 2018 IRC Section M1504.2.
Duct length is calculated with the same formulas used to develop 2015 IRC Table M1506.2 and 2018 IRC Table M1504.2 (i.e., the Darcy-Weisbach-Colebrook equations). Assumptions are consistent with these tables (i.e., 15' for elbows, 30' for a termination fitting, standard temperature and pressure, and roughness factors of 0.0055' for flex ducts and 0.00038' for smooth ducts).
Actual results may vary based on differences in equipment, materials, and installation. Compression of flex ducts by as little as 5% can significantly reduce flow.
Fan curves are based on test data determined in accordance with ANSI/AMCA 210-ANSI/ASHRAE 51 and HVI 916.