AllDuctCalc™ - HVAC Air Duct Calculator v2 Updated 10/26/15 Provide inputs in the blue boxes, other inputs optional.
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Duct Type Friction Loss Rate Airflow
Duct Type
Length
Airflow
Duct Type
Length
Diameter
Duct Type
Length Friction Loss
Non-Round Shape
Units
Adjustable Absolute  Duct Roughness
If selected, Flexible roughness is 0.003 ft when
straight and fully stretched tight at 0% compression
(adjusted at other compressions), otherwise the
original method of constant 0.01 ft roughness is used.
 Use ASH RAE 2013 Flex Compression
Smooth PVC or Aluminum mm ft
Unit Converter
Med.smooth mm ft Compression  = 1−(L ∕ LFE)
Medium mm ft
L = Installed Length
Med.Rough Fibrous Board mm ft
LFE = Fully Extended Length
Fibrous Liner mm ft
Rough Flexible Metalic mm ft

http://www.engineeringtoolbox.com/colebrook-equation-d_1031.html     Recritical  = 2000

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