ResDuct - Residential Air Duct Calculator v1.53 Enter and adjust the parameters in the blue boxes. Click the "Calculate" button for the results.
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      Friction Rate   "wc/100ft ACCA Manual D recommended
Residential Velocities (feet per minute)
  Supply     Return    
Duct Type        Supply Return  
Run Type        Rigid Flex Rigid or Flex  
Airflow - CFM        Trunk  700 600 600  
  Enter airflows, and click the "Calculate" button for results. Branch  600 600 400  
900fpm limit 700fpm limit Maximum  900 700 700  
  Exceeding maximum increases restriction, noise
and renders fittings' equivalent length inaccurate.
  Allow to exceed maximum by:     fpm  
    Velocity Calculator  
Compression   Side(a)   N/A     Diameter CFM      
Select 4" to 10" x x     @ = 1019 fpm
11" to 17" x x Side(a) Side(b) CFM      
18" to 24" x x x @ = 1200 fpm

This Ductulator uses the Colebrook equation to calculate the smallest duct size acceptable for the selected friction rate and duct type that stays within the selected ACCA Manual D recommended velocities. Unless within 2%, the diameter is rounded up to the nearest inch. Rectangular duct is rounded up to the nearest 1/4 inch. Calculations are for 60°F dry air at sea level, from 5 to 3000 cfm (approximately standard air which is 0.075lbda/ft³). If "ASHRAE 2013" is 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.

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