The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section M1506.3. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.
Exception: Whole-house ventilation-type attic fans that discharge into the attic space of dwelling units having private attics shall be permitted.
Exception: Whole-house ventilation-type attic fans that discharge into the attic space of dwelling units having private attics shall be permitted.
Clothes dryers shall be exhausted in accordance with the manufacturer's instructions.
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.
Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.
Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be
made with a full opening exhaust outlet or
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 into buildings. Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination.
Exhaust ducts shall have a smooth interior finish and be constructed of metal having a minimum thickness of 0.0157 inches (0.3950 mm) (No. 28 gage). The duct shall be 4 inches (102 mm) nominal in diameter.
Exhaust ducts shall be supported at intervals not to exceed 4 feet (1219 mm) and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1. Ducts shall not be joined with screws or similar fasteners that protrude into the inside of the duct.
Transition ducts used to connect the dryer to the exhaust duct system shall be a single
length.
Transition ducts shall be not greater than 8 feet (2438 mm) in length. Transition ducts shall not be concealed within construction.
Domestic dryer exhaust duct power ventilators shall conform to UL 705 for use in dryer exhaust duct systems. The dryer exhaust duct power ventilator shall be installed in accordance with the manufacturer's instructions.
The maximum allowable exhaust duct length shall be determined by one of the methods specified in Sections M1502.4.5.1 through M1502.4.5.3.
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.
The size and maximum length of the exhaust duct shall be determined by the dryer manufacturer's installation instructions. The code official shall be provided with a copy of the installation instructions for the make and model of the dryer at the concealment inspection. In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table M1502.4.5.1 shall be used.
The maximum length of the exhaust duct shall be determined in accordance with the manufacturer's instructions for the dryer exhaust duct power ventilator.
Where the exhaust duct equivalent length exceeds 35 feet (10 668 mm), the equivalent length of the exhaust duct shall be identified on a permanent label or tag. The label or tag shall be located within 6 feet (1829 mm) of the exhaust duct connection.
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.
Exception: Where a listed condensing clothes dryer is installed prior to occupancy of the structure.
Protective shield plates shall be placed where nails or screws from finish or other work are likely to penetrate the clothes dryer exhaust duct. Shield plates shall be placed on the finished face of framing members where there is less than 11/4 inches (32 mm) between the duct and the finished face of the framing member. Protective shield plates shall be constructed of steel, shall have a minimum thickness of 0.062-inch (1.6 mm) and shall extend not less than 2 inches (51 mm) above sole plates and below top plates.
Ducts that exhaust clothes
dryers shall not penetrate or be located within any fire-blocking,
draft-stopping or any wall, floor/ceiling or other assembly
required by this code to be fire-resistance rated, unless
such duct is constructed of galvanized steel or aluminum of
the thickness specified in Table M1601.1.1 and the fire-resistance
rating is maintained in accordance with Section R302.
Fire dampers, combination fire/smoke dampers and any similar
devices that will obstruct the exhaust flow, shall be prohibited
in clothes dryer exhaust ducts.
Installations exhausting more than
200 cfm (0.09 m3/s) shall be provided with makeup air.
Where a closet is designed for the installation of a clothes
dryer, an opening having an area of not less than 100 square
inches (0.0645 m2) shall be provided in the closet enclosure.
Range hoods shall discharge to the outdoors through a duct. The duct serving the hood shall have a smooth interior surface, shall be air tight, shall be equipped with a back-draft damper and shall be independent of all other exhaust systems. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building.
Ducts serving range hoods shall be constructed of galvanized steel, stainless steel or copper.
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.
Overhead exhaust hoods shall be constructed
of metal, not less than 0.016 inch (0.4 mm) (No. 28
gage).
Exception:
- Combination microwave oven/ventilating hoods installed in accordance with Section M1504.1.
- Down-draft exhaust systems.
Domestic kitchen cooking appliances
shall be
equipped with ducted range hoods or down-draft exhaust systems, the fans shall be sized in accordance with Section M1507.4.
Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be mechanically or naturally provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with not less than one damper. Each damper shall be a gravity damper or an electrically operated damper that automatically opens when the exhaust system operates. Dampers shall be accessible for inspection, service, repair and replacement without removing permanent construction or any other ducts not connected to the damper being inspected, serviced, repaired or replaced.
Kitchen exhaust makeup air shall be discharged into the same room in which the exhaust system is located or into rooms or duct systems that communicate through one or more permanent openings with the room in which such exhaust system is located. Such permanent openings shall have a net cross-sectional area not less than the required area of the makeup air supply openings.
Domestic open-top broiler units shall have a metal exhaust hood, having a minimum thickness of 0.0157-inch (0.3950 mm) (No. 28 gage) with 1/4 inch (6.4 mm) clearance between the hood and the underside of combustible material or cabinets.
The hood shall be not less than the width of the broiler unit, extend over the entire unit, discharge to the outdoors and be equipped with a backdraft damper or other means to control infiltration/exfiltration when not in operation. Broiler units incorporating an integral exhaust system, and listed and labeled for use without an exhaust hood, need not have an exhaust hood.
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.
| FAN TESTED CFM @ 0.10 IN. W.G. |
MINIMUM METAL FLEX (DIAMETER) (inches) |
MAXIMUM LENGTH (feet) |
MINIMUM SMOOTH (DIAMETER) (inches) |
MAXIMUM LENGTH (feet) |
MAXIMUM ELBOWSa |
| 50 | 4 | 25 | 4 | 70 | 3 |
| 5 | 90 | 5 | 100 | 3 | |
| 6 | No limit | 6 | No limit | 3 | |
| 80 | 4b | N/A | 4 | 20 | 3 |
| 5 | 15 | 5 | 100 | 3 | |
| 6 | 90 | 6 | No limit | 3 | |
| 100 | 5b | N/A | 5 | 50 | 3 |
| 6 | 45 | 6 | No limit | 3 | |
| 125 | 6 | 15 | 6 | No limit | 3 |
| 7 | 70 | 7 | No limit | 3 | |
| 160 | 6 | 4 | 6 | 40 | 3 |
| 7 | 50 | 7 | 100 | 3 |
- For each additional elbow subtract 10 feet from length.
- Metal flex ducts of this diameter are not permitted with fans of this size.
Air exhaust openings shall terminate not less than 3 feet (914 mm) from
operable and nonoperable openings into the building and 10 feet (3048 mm) from mechanical air intakes except where the opening is located 3 feet (914 mm) above the air intake. Openings shall comply with Sections
R303.4.2 and R303.5.
Where Section R303.3 requires toilet
rooms, bathrooms and rooms with bathing or spa facilities to
be mechanically ventilated, the ventilation equipment shall be
installed per this section.
Where local exhaust or whole-house mechanical ventilation is provided, the equipment shall be designed in accordance with this section.
Exhaust air from
range
hoods,
bathrooms,
toilet rooms,
and rooms with bathing or
spa facilities
shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from
range hoods,
bathrooms,
toilet rooms,
and rooms with bathing or spa facilities
shall not discharge into an attic, crawl space or other areas inside the building.
When installed,
whole-house mechanical ventilation systems shall be designed in accordance with Sections M1507.3.1 through M1507.3.3.
The whole-house ventilation system shall consist of one or more supply or exhaust fans, or a combination of such, and associated ducts and controls. Local exhaust or supply fans are permitted to serve as such a system. Outdoor air ducts connected to the return side of an air handler shall be considered as providing supply ventilation.
The whole-house mechanical ventilation system shall be provided with controls that enable manual override.
The whole-house mechanical ventilation system shall provide outdoor air at a continuous rate of not less than that determined in accordance with Table M1507.3.3(1).
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 M1507.3.3(1) is multiplied by the factor determined in accordance with Table M1507.3.3(2).
| DWELLING UNIT FLOOR AREA (square feet) |
NUMBER OF BEDROOMS | ||||
| 0 — 1 | 2 — 3 | 4 — 5 | 6 — 7 | > 7 | |
| Airflow in CFM | |||||
| < 1,500 | 30 | 45 | 60 | 75 | 90 |
| 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 |
| > 7,500 | 105 | 120 | 135 | 150 | 165 |
For SI: 1 square foot = 0.0929 m2, 1 cubic foot per minute = 0.0004719 m3/s.
| RUN-TIME PERCENTAGE IN EACH 4-HOUR SEGMENT |
25% | 33% | 50% | 66% | 75% | 100% |
| Factora | 4 | 3 | 2 | 1.5 | 1.3 | 1.0 |
- For ventilation system run time values between those given, the factors are permitted to be determined by interpolation.
- Extrapolation beyond the table is prohibited.
Ventilation systems shall be designed to have the capacity to exhaust the minimum air flow rate determined in accordance with Table M1507.4. Exhaust flow ratings shall be source specific ventilation systems in accordance with the Home Ventilating Institute (HVI) or Air Movement and Control Association (AMCA) residential ventilation standards.
For SI: 1 cubic foot per minute = 0.0004719 m3/s.
| DOMESTIC KITCHENS | |
| Range hoods/downdraft exhaust. | Min. 150 cfm intermittent |
| BATHROOMS—TOILET ROOMS | |
| Rooms containing bathing and spa facilities. (Static pressure shall be rated @ 0.10-inch water gauge for intermittent fans.) |
Min. 80 cfm intermittent or 20 cfm continuous |
| Toilet rooms without bathing or spa facilities, when not provided with natural ventilation in accordance with Section R303.3.2. |
Min. 50 cfm |
Continuous
ventilation fans shall be rated for sound at a maximum
of 1.0 sone.
Intermittent fans shall
be rated for sound at a maximum of 3 sones, unless the
maximum rated airflow exceeds 400 cfm (200 L/s).
Remotely installed fans that are at least 4 feet (1220 mm) away from the inlet grill are exempt from the sone rating requirements of M1507.4.1.1.
All rooms
containing bathing or spa facilities shall be provided with a
mechanical ventilation system controlled by a dehumidistat,
timer or similar means of automatic control.