Dryer exhaust systems shall be independent of all other systems and shall convey the moisture to the outdoors.
Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.
The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. Where fittings are used, the maximum length of the exhaust duct shall be reduced in accordance with Table M1502.4.5.1. The maximum length of the exhaust duct does not include the transition duct.
|DRYER EXHAUST DUCT FITTING TYPE||EQUIVALENT LENGTH|
|4-inch radius mitered 45-degree elbow||2 feet 6 inches|
|4-inch radius mitered 90-degree elbow||5 feet|
|6-inch radius smooth 45-degree elbow||1 foot|
|6-inch radius smooth 90-degree elbow||1 foot 9 inches|
|8-inch radius smooth 45-degree elbow||1 foot|
|8-inch radius smooth 90-degree elbow||1 foot 7 inches|
|10-inch radius smooth 45-degree elbow||9 inches|
|10-inch radius smooth 90-degree elbow||1 foot 6 inches|
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.0175 rad.
Where space for a clothes dryer is provided, an exhaust duct system shall be installed. Where the clothes dryer is not installed at the time of occupancy the exhaust duct shall be capped or plugged in the space in which it originates and identified and marked "future use."
Exception: Where a listed condensing clothes dryer is installed prior to occupancy of the structure.
Where domestic cooking exhaust equipment is provided, it shall comply with one of the following:
- The fan for overhead range hoods and downdraft exhaust equipment not integral with the cooking appliance shall be listed and labeled in accordance with UL 507.
- Overhead range hoods and downdraft exhaust equipment with integral fans shall comply with UL 507.
- Domestic cooking appliances with integral downdraft exhaust equipment shall be listed and labeled in accordance with ANSI Z21.1 or UL 858.
- Microwave ovens with integral exhaust for installation over the cooking surface shall be listed and labeled in accordance with UL 923.
Domestic open-top broiler units shall be provided with a metal exhaust hood having a thickness of not less than 0.0157 inch (0.3950 mm) (No. 28 gage). Such hoods shall be installed with a clearance of not less than 1/4 inch (6.4 mm) between the hood and the underside of combustible material and cabinets. A clearance of not less than 24 inches (610 mm) shall be maintained between the cooking surface and combustible material and cabinets. The hood width shall be not less than the width of the broiler unit and shall extend over the entire unit.
Exception: Broiler units that incorporate an integral exhaust system, and that are listed and labeled for use without an exhaust hood, shall not be required to have an exhaust hood.
Domestic cooking exhaust equipment shall discharge to the outdoors through a duct. The duct shall have a smooth interior surface, shall be air tight, shall be equipped with a backdraft damper and shall be independent of all other exhaust systems. Ducts serving domestic cooking exhaust equipment shall not terminate in an attic or crawl space or areas inside the building.
Exception: Where installed in accordance with the manufacturer's instructions, and where mechanical or natural ventilation is otherwise provided, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.
Exception: Ducts for domestic kitchen cooking appliances equipped with down-draft exhaust systems shall be permitted to be constructed of schedule 40 PVC pipe and fittings provided that the installation complies with all of the following:
- The duct is installed under a concrete slab poured on grade.
- The underfloor trench in which the duct is installed is completely backfilled with sand or gravel.
- The PVC duct extends not more than 1 inch (25 mm) above the indoor concrete floor surface.
- The PVC duct extends not more than 1 inch (25 mm) above grade outside of the building.
- The PVC ducts are solvent cemented.
Where one or more gas, liquid or solid fuel-burning appliance that is neither direct-vent nor uses a mechanical draft venting system is located within a dwelling unit's air barrier, each exhaust system capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be mechanically or passively provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with not fewer than one damper complying with Section M1503.6.2.
Exception: Makeup air is not required for exhaust systems installed for the exclusive purpose of space cooling and intended to be operated only when windows or other air inlets are open.
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.
|DUCT TYPE||FLEX DUCT||SMOOTH-WALL DUCT|
|Fan airflow rating|
(CFM @ 0.25 inch wca)
|Maximum lengthc, d, e|
|8 and above||NL||NL||NL||NL||NL||189||111||69||NL||NL||NL||NL||NL||NL||198||133|
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
- Fan airflow rating shall be in accordance with ANSI/AMCA 210-ANSI/ASHRAE 51.
- For noncircular ducts, calculate the diameter as four times the cross-sectional area divided by the perimeter.
- 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.
- NL = no limit on duct length of this size.
- 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 terminate as follows:
- Not less than 3 feet (914 mm) from property lines.
- Not less than 3 feet (914 mm) from gravity air intake openings, operable windows and doors.
- Not less than 10 feet (3048 mm) from mechanical air intake openings except where the exhaust opening is located not less than 3 feet (914 mm) above the air intake opening. Openings shall comply with Sections R303.5.2 and R303.6.
Exception: The whole-house mechanical ventilation system is permitted to operate intermittently where the system has controls that enable operation for not less than 25 percent of each 4-hour segment and the ventilation rate prescribed in Table M1505.4.3(1) is multiplied by the factor determined in accordance with Table M1505.4.3(2).
CONTINUOUS WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM AIRFLOW RATE REQUIREMENTS
|NUMBER OF BEDROOMS|
|0 — 1||2 — 3||4 — 5||6 — 7||> 7|
|Airflow in CFM|
|1,501 — 3,000||45||60||75||90||105|
|3,001 — 4,500||60||75||90||105||120|
|4,501 — 6,000||75||90||105||120||135|
|6,001 — 7,500||90||105||120||135||150|
For SI: 1 square foot = 0.0929 m2, 1 cubic foot per minute = 0.0004719 m3/s.
INTERMITTENT WHOLE-HOUSE MECHANICAL VENTILATION RATE FACTORSa, b
|RUN-TIME PERCENTAGE IN EACH 4-HOUR|
- For ventilation system run time values between those given, the factors are permitted to be determined by interpolation.
- Extrapolation beyond the table is prohibited.
|AREA TO BE |
|Kitchens||100 cfm intermittent or 25 cfm continuous|
|Mechanical exhaust capacity of 50 cfm|
intermittent or 20 cfm continuous
For SI: 1 cubic foot per minute = 0.0004719 m3/s.