About this chapter: Chapter 15 is specific to exhaust systems related to clothes dryers, domestic cooking, toilet rooms, bathrooms and whole-house ventilation systems. Included are requirements for exhaust discharge locations, protection of exhaust ducts from damage, exhaust duct construction, duct length limits, and exhaust termination clearances. This chapter contains prohibitions for exhaust recirculation and discharge locations and addresses the design of whole-house ventilation systems required by Chapter 3.
Dryer exhaust systems shall be independent of all other systems and shall convey the moisture to the outdoors.
|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:
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.
Domestic cooking exhaust equipment shall discharge to the outdoors through a duct. The duct shall have a smooth interior surface, shall be airtight, 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.
Ducts serving domestic cooking exhaust equipment shall be constructed of galvanized steel, stainless steel or copper.
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.
The length of exhaust and supply ducts used with ventilating equipment shall not exceed the lengths determined in accordance with Table M1504.2.
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.
|DUCT TYPE||FLEX DUCT||SMOOTH-WALL DUCT|
|Fan airflow rating (CFM @ 0.25 inch wca)||50||80||100||125||150||200||250||300||50||80||100||125||150||200||250||300|
|Diameterb (inches)||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.
Air exhaust openings shall terminate as follows:
The whole-house mechanical ventilation system shall provide outdoor air at a continuous rate not less than that determined in accordance with Table M1505.4.3(1) or not less than that determined by Equation 15-1.
|DWELLING UNIT FLOOR AREA (square feet)||NUMBER OF BEDROOMS|
|Airflow in CFM|
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 SEGMENT||25%||33%||50%||66%||75%||100%|
ONE- AND TWO-FAMILY DWELLINGS
|AREA TO BE EXHAUSTED||EXHAUST RATESa|
|Kitchens||100 cfm intermittent or 25 cfm continuous|
|Bathrooms-Toilet Rooms||Mechanical exhaust capacity of 50 cfm intermittent or 20 cfm continuous|
For SI: 1 cubic foot per minute = 0.0004719 m3/s, 1 inch water column = 0.2488 kPa.
- The listed exhaust rate for bathrooms-toilet rooms shall equal or exceed the exhaust rate at a minimum static pressure of 0.25 inch water column in accordance with Section M1505.3.