This is a simplified breakdown of cfm for standard ductwork. ***This is only a guideline. A manual D is needed to be official.****

 

 

Online Duct Calculator

 

WHAT IS MY CFM?

5” ROUND = 65 CFM

8X8 DUCT = 275 CFM

6” ROUND = 100 CFM

10X8 DUCT = 375 CFM

7” ROUND = 150 CFM

12X8 DUCT = 475 CFM

8” ROUND = 225 CFM

14X8 DUCT = 575 CFM

9” ROUND = 275 CFM

16X8 DUCT = 700 CFM

10” ROUND = 380 CFM

18X8 DUCT = 800 CFM

20X8 DUCT = 900 CFM

22X8 DUCT = 1000 CFM

24X8 DUCT = 1125 CFM

 

*BASED ON .08 FRICTION LOSS

*BASED ON A FACE VELOCITY OF 400FPM

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SUPPLY AIR REGISTERS RETURN GRILLES

4X10 (421) = 120 CFM

14X6 (650) = 160 CFM

4X12 (421) = 140 CFM

30X6 (650) = 340 CFM

2X10 (420) = 60 CFM

2X12 (420) = 70 CFM

10X6 (661) = 170 CFM

 

*BASED ON A FACE VELOCITY OF 700FPM *THIS TABLE IS DESIGNED TO BE A GUIDELINE ONLY, SO CONTRACTORS CAN QUICKLY EVALUATE A DUCT SYSTEM TO SECURE A FURNACE OR AIR CONDITIONING SALE. *THIS TABLE IS NOT TO BE USED TO REPLACE A PROPER MANUAL D DESIGN.