This document provides guidelines for maximum friction losses and velocities for different types of air ducts based on CFM flow rates. It outlines standards for transfer air ducts, gravity relief air shifts, low pressure ducts, toilets exhaust ducts, high pressure ducts, medium pressure ducts, dish washer exhaust ducts, kitchen hood exhaust ducts, acid and solvent stacks, and outside air shifts. Ranges are given for maximum friction in inches of water gauge per 100 feet and maximum velocities in feet per minute.

1. 1. TRANSFER AIR DUCT
2. GRAVITY RELIEF AIR SHIFTS
 MAX FRICTION = 0.03-0.05
in.w.g/100ft
WHEN CFM < 3200
CFM
 MAX VELOCITY = 1000
fpm
WHEN
CFM > 3200
CFM
1. LOW PRESSSURE DUCT
2. GENERAL EXHAUST DUCT
3. TOILETS EXHAUST DUCT
 MAX FRICTION = 0.1-0.15
in.w.g/100ft
WHEN CFM <6000
CFM
 MAX VELOCITY = 1500-1800
fpm
WHEN CFM >6000
CFM
 APPLICABLE FOR SUPPLY,RETURN,EXHAUST AND OUT SIDE AIR
HIGH PRESSSURE DUCT
 MAX FRICTION= 0.4-0.45
in.w.g/100ft
WHEN CFM < 5000
CFM
 MAX VELOCITY = 2500-3500
fpm
WHEN CFM > 5000
CFM
 APPLICABLEFOR SUPPLY SYSTEM ONLY
0033 CFM
0033 CFM
6000 CFM
ACID AMMONIA AND SOLVENTS MAINS
 MAX FRICTION=0.5-0.6
in.w.g/100ft
 MAX VELOCITY =3000
fpm
 MIN VELOCITY =1000
fpm
 MAIN & RISER = 1500-3000 fpm
 BRANCHES & LATERALS = 1000-2000 fpm
MEDIUM PRESSSURE DUCT
 MAX FRICTION = 0.2-0.25
in.w.g/100ft
WHEN CFM < 6000
CFM
 MAX VELOCITY = 2000-2500
fpm
WHEN CFM > 6000
CFM
 APPLICABLEFOR SUPPLY SYSTEM
ONLY
DISH WASHER
EXHAUST DUCT
 MAX FRICTION=0.1-
0.15
in.w.g/100ft
 MAX VELOCITY
=2200
FPM
 MIN VELOCITY 1500
FPM
KITCHEN HOOD EXHAUST DUCT
 MAX VELOCITY =2200
FPM
 MIN VELOCITY 1500
FPM
ACID , AMMONIA AND SOLVENT STACKS
 MAX VELOCITY =4000
CFM
 MIN VELOCITY =3000
CFM
 700FPM ( EXHAUST OR RELIEF )
 MAXIMUM VELOCITY THROUGH FREE AREA
:ASSUMING 50% FREE AREA-MAX.VELOCITY
350 FPM THROUGH GROSS AREA
 500FPM ( INTAKE )
 MAXIMUM VELOCITY THROUGH FREE AREA
:ASSUMING 50% FREE AREA-MAX.VELOCITY
250 FPM THROUGH GROSS AREA
 MIN 250FPM ( SILANE DUCT )
 VELOCITY ACROSS THE NECK OF CYLINDER OR
CABINET WINDOW OR ACCESS PORT
MUSTAFA A. ABDULJABBAR
Mustafahmed94@yahoo.com
Mobile 00971 50 499 50 43
OUTSIDE AIR SHIFT
 MAX FRICTION = 0.05-
0.1
in.w.g/100ft
WHEN CFM <
1200
CFM
 MAX VELOCITY = 1000
fpm
WHEN CFM > 1200
CFM