Section M1506 Exhaust Ducts and Exhaust Openings

Where exhaust duct construction is not specified in this chapter, construction shall comply with Chapter 16. The length of exhaust and supply ducts used with ventilating equipment shall not exceed the lengths determined in accordance with Table M1506.2. Exception: Duct length shall not be limited where the duct system complies with the manufacturer's design criteria or where the flow rate of the installed ventilating equipment is verified by the installer or approved third party using a flow hood, flow grid or other airflow measuring device. TABLE M1506.2 DUCT LENGTH DUCT TYPE FLEX DUCT SMOOTH-WALL DUCT Fan airflow rating (CFM @ 0.25 inch wc a ) 50 80 100 125 150 200 250 300 50 80 100 125 150 200 250 300 Diameter b (inches) Maximum length c, d, e (feet) 3 X X X X X X X X 5 X X X X X X X 4 56 4 X X X X X X 114 31 10 X X X X X 5 NL 81 42 16 2 X X X NL 152 91 51 28 4 X X 6 NL NL 158 91 55 18 1 X NL NL NL 168 112 53 25 9 7 NL NL NL NL 161 78 40 19 NL NL NL NL NL 148 88 54 8 and above NL NL NL NL NL 189 111 69 NL NL NL NL NL NL 198 133 For SI: 1 foot = 304.8 mm. a. Fan airflow rating shall be in acordance with ANSI/AMCA 210-ANSI/ASHRAE 51. b. For noncircular ducts, calculate the diameter as four times the cross-sectional area divided by the perimeter. c. This table assumes that elbows are not used. Fifteen feet of allowable duct length shall be deducted for each elbow installed in the duct run. d. NL = no limit on duct length of this size. e. X = not allowed. Any length of duct of this size with assumed turns and fittings will exceed the rated pressure drop. Air exhaust openings shall ...

Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer's installation instructions. If the manufacturer's instructions do not specify a termination location, the exhaust duct shall terminate not less than 3 feet (914 mm) in any direction from openings ...

Where ductwork is large enough to allow entry of personnel, not less than one approved or listed opening having dimensions not less than 22 ...

Exhaust ducts shall be constructed of steel and shall be substantially supported. Exhaust ducts without dampers are preferred; however, if dampers are installed, they shall be maintained so that they will be in a full open position ...

Exhaust ducts shall be protected against mechanical damage and have a clearance from unprotected combustible construction or other combustible material of not less than 18 inches (45.72 cm). If combustible construction is provided with the following protection applied to all surfaces within 18 inches (45.72 cm), clearances may be reduced to the distances indicated: (a) 28-gage sheet metal on 1/4-inch asbestos mill board. 12 inches (30.48 cm). (b) 28-gage sheet metal on 1/8-inch asbestos mill board spaced out 1 inch (2.54 cm) on noncombustible spacers. 9 inches (22.86 cm). (c) 22-gage sheet metal on 1-inch rockwool batts reinforced with wire mesh or the equivalent. 3 inches (7.62 cm). (d) Where ducts are protected with an approved automatic sprinkler, system, properly maintained, the clearance required in paragraph (d)(7)(i) of this section may be reduced to 6 inches (15.24 cm). Exhaust ducts shall be constructed of steel and shall be substantially supported. Exhaust ducts without dampers are preferred; however, if dampers are installed, they shall be maintained so that they will be in a full open position at all times the ventilating system is in operation.  ...