Air duct sizing calculator

"So easy, your dog can do it!".
No fluff, no unnecessary tabs or screens. Perform all your duct sizing using only one screen with your android device

Three entries is all you need to size duct. (imperial or metric units)
(1) Select duct type
(2) Enter the friction rate
(3) Enter CFM
The velocity and round duct size is immediately displayed using the equal friction/recommended velocity methodology. The same methodology as used with ACCA Manual D

A handy "round to rectangular" calculator is also included. The rectangular size is adjusted for the increased friction loss encountered with square and rectangular duct.

How to size duct with the EMS air duct calculator: (Sample below)

Type duct: metal supply trunk with flexible runs and flexible return duct.
System total CFM = 1200
Friction rate = .08 ( A friction rate of .04 -.08"wc will provide a quiet system with adequate air flow for most residences. The lower the friction rate the quieter the system. Unusually lengthy or complex systems should be sized using the lower friction rate). For a full explanation for calculating friction rate go to http://johnrwhite.net/three%20steps%20to%20duct%20sizing.htm

Procedure:
Sizing supply trunk:(see screenshot)
(1) Select type of duct - METAL
(2) Enter friction rate - .08 ( use the same friction rate for the entire duct sytem)
(3) Enter CFM- 1200
Read round duct size is 15.7 inches (16" nominal)- Notice velocity is 907 ft./min. 900 fpm is the limit for metal duct, however, since we are actually using 16" duct the velocity will fall to an acceptable level

Sizing flexible runs; Not shown in screenshot
(1) Select type of duct - FLEX
(2) Enter the first run CFM (If you wish to deliver 150 cfm to a room using one run, enter 150.
(3) Read flex duct size is 7.8 inches (8" nominal), fpm is 452, which is acceptable.
(4) Repeat 1, 2 and three for each run in the system.

Sizing the return trunk: Not shown in screenshot
(1) Select type of duct - FLEX
(2) Enter CFM - 1200
(3) Read flex duct size is 17.2 inches (18" nominal); velocity is 750 fpm which is slightly over recommended, however, since the actual duct size will be 18", the velocity will fall to an acceptable level

Converting round duct sizes to rectangular duct size:
Suppose you wish to make the supply duct rectangular. First determine the height you wish to make it (8") then read the width (28.1"). Therefore, the duct will be 8" x 28.1"

That's all there is to it, Hope you enjoy the EMS air duct calculator