User note: Code change proposals to this chapter will be considered by the IRC ‒ Plumbing and Mechanical Code Development Committee during the 2015 (Group A) Code Development Cycle.
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 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 12 feet (3658 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 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude more than 1/8 inch (3.2 mm) into the inside of the duct.
Transition ducts used to connect the dryer to the exhaust duct system shall be a single length that is listed and labeled in accordance with UL 2158A. 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.
TABLE M1502.4.5.1 DRYER EXHAUST DUCT FITTING EQUIVALENT LENGTH
TABLE M1502.4.5.1 DRYER EXHAUST DUCT FITTING EQUIVALENT LENGTH
| 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.
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.
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: 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 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.
Where domestic kitchen cooking appliances are 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. A clearance of not less than 24 inches (610 mm) shall be maintained between the cooking surface and the combustible material or cabinet. The hood shall be not less than the width of the broiler unit, extend over the entire unit, and when located inside the building envelope, shall 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, or broiler units permanently installed outside the building envelope and having the cooking surface at least 5'0" below a 1-hour fire resistance rated ceiling, 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.
TABLE M1506.2 DUCT LENGTH
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 wca) | 50 | 80 | 100 | 125 | 150 | 200 | 250 | 300 | 50 | 80 | 100 | 125 | 150 | 200 | 250 | 300 |
| Diameterb (inches) | Maximum lengthc, 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 terminate not less than 3 feet (914 mm) from property lines; 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 R303.5.2 and R303.6.
Where Local exhaust or and whole-house mechanical ventilation is provided, the systems and equipment shall be designed in accordance with this section.
Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside of the building.
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.
Each dwelling unit or guestroom
shall be equipped with a ventilation system complying with
Section M1507.3.4, M1507.3.5, M1507.3.6 or M1507.3.7.
Compliance is also permitted to be demonstrated through
compliance with the International Mechanical Code or
ASHRAE Standard 62.2.
The whole-house mechanical ventilation system shall be provided with controls that enable manual override.
- Location of controls. Controls for all ventilation systems shall be readily accessible by the occupant.
- Instructions. Operating instructions for whole-house ventilation systems shall be provided to the occupant by the installer of the system.
- Local exhaust systems. Local exhaust systems shall be controlled by manual switches, dehumidistats, timers, or other approved means
- Continuous whole-house ventilation systems. Continuous whole-house ventilation systems shall operate continuously and be equipped with an override control. A "fan on" switch shall be permitted as an override control. Controls shall be capable of operating the ventilation system without energizing other energy-consuming appliances. A clearly visible label shall be affixed to the controls that reads "Whole House Ventilation (see operating instructions)."
- Intermittent whole-house ventilation systems.
Intermittent whole-house ventilation systems shall
comply with the following:
- They shall be capable of operating intermittently and continuously.
- They shall have controls capable of operating the exhaust fans, forced-air system fans, or supply fans without energizing other energy-consuming appliances.
- The ventilation rate shall be adjusted according to the exception in Section M1507.3.3.
- The system shall be designed so that it can operate automatically based on the type of control timer installed.
- The intermittent mechanical ventilation system shall operate at least one hour out of every four.
- The system shall have a manual control and automatic control, such as a 24-hour clock timer.
- At the time of final inspection, the automatic control shall be set to operate the whole-house fan according to the schedule used to calculate the whole-house fan sizing.
- A label shall be affixed to the control that reads "Whole House Ventilation (see operating instructions).
Installers shall
provide the manufacturer's installation, operating
instructions, and a whole-house ventilation system
operation description.
The whole-house mechanical ventilation system shall provide outdoor air to each dwelling unit at a continuous rate of not less than that determined in accordance with Table M1507.3.3(1).
TABLE M1507.3.3(1) CONTINUOUS WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM AIRFLOW RATE REQUIREMENTS
TABLE M1507.3.3(2) INTERMITTENT WHOLE-HOUSE MECHANICAL VENTILATION RATE FACTORSa, b
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).
TABLE M1507.3.3(1) CONTINUOUS WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM AIRFLOW RATE REQUIREMENTS
| 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.
TABLE M1507.3.3(2) INTERMITTENT WHOLE-HOUSE MECHANICAL VENTILATION RATE FACTORSa, b
| RUN-TIME PERCENTAGE IN EACH 4-HOUR SEGMENT | 25% | 33% | 50% | 66% | 75% | 100% |
| Factora | 4 | 3 | 2 | 1.5 | 1.3 | 1.0 |
| a. For ventilation system run time values between those given, the factors are permitted to be determined by interpolation. |
| b. Extrapolation beyond the table is prohibited. |
Whole-house fans located 4 feet
or less from the interior grille shall have a sone rating of
1.0 or less measured at 0.1 inches water gauge.
Manufacturer's noise ratings shall be determined as per HVI 915 (March 2009). Remotely mounted fans shall be acoustically isolated from the structural elements of the building and from attached duct work using insulated flexible duct or other approved material.
Manufacturer's noise ratings shall be determined as per HVI 915 (March 2009). Remotely mounted fans shall be acoustically isolated from the structural elements of the building and from attached duct work using insulated flexible duct or other approved material.
Each habitable space
shall be provided with outdoor air inlets or operable
windows with an openable area not less than 4 square
inches of net free area of opening for each 10 cfm of
outdoor air required by Table M1507.3.3(1). Where
outdoor air supplies are separated from exhaust points by
doors, provisions shall be made to ensure air flow by
installation of distribution ducts, undercutting doors,
installation of grilles, transoms, or similar means. Doors
shall be undercut to a minimum of 1/2 inch above the
surface of the finish floor covering.
Individual room outdoor air inlets shall:
Individual room outdoor air inlets shall:
- Have controllable and secure openings;
- Be sleeved or otherwise designed so as not to compromise the thermal properties of the wall or window in which they are placed;
- Any inlet or combination of inlets which provide 10 cfm at 10 Pascals are deemed equivalent to 4 square inches net free area.
- Closer than 10 feet from an appliance vent outlet, unless such vent outlet is 3 feet above the outdoor air inlet.
- Where it will pick up objectionable odors, fumes or flammable vapors.
- A hazardous or unsanitary location.
- A room or space having any fuel-burning appliances therein.
- Closer than 10 feet from a vent opening of a plumbing drainage system unless the vent opening is at least 3 feet above the air inlet.
- Attic, crawl spaces, or garages.
- Asphalt roofs unless it is shown that no other location is permissible. In such cases the inlet opening shall be located a minimum of 2 feet from the nearest surface of the asphalt roofing, measured from the intake opening.
Integrated whole-house ventilation systems
shall provide outdoor air at the rate calculated using
Section M1507.3.3. Integrated forced-air ventilation
systems shall distribute outdoor air to each habitable
space through the forced-air system ducts. Integrated
forced-air ventilation systems shall have an outdoor air
inlet duct connecting a terminal element on the outside of
the building to the return air plenum of the forced-air
system, at a point within 4 feet upstream of the air
handler. The outdoor air inlet duct connection to the
return air stream shall be located upstream of the forced-air
system blower and shall not be connected directly into
a furnace cabinet to prevent thermal shock to the heat
exchanger. The system will be equipped with a motorized
damper connected to the automatic ventilation control as
specified in Section M1507.3.2. The required flow rate
shall be verified by field testing with a flow hood or a
flow measuring station
Inlets shall be screened
or otherwise protected from entry by leaves or other
material. Outdoor air inlets shall be located so as not to
take air from the following areas:
- Closer than 10 feet from an appliance vent outlet, unless such vent outlet is 3 feet above the outdoor air inlet.
- Where it will pick up objectionable odors, fumes or flammable vapors.
- A hazardous or unsanitary location.
- A room or space having any fuel-burning appliances therein.
- Closer than 10 feet from a vent opening of a plumbing drainage system unless the vent opening is at least 3 feet above the air inlet.
- Attic, crawl spaces, or garages.
Supply fan ventilation
systems shall distribute outdoor air to each habitable
space through the forced-air system ducts or through
dedicated ducts to each habitable space. Supply fans shall
have the capacity to provide the amount of outdoor air
specified in Table M1507.3.3(1) at 0.40 inches water
gauge as per HVI 916. The outdoor air must be filtered
before it is delivered to habitable spaces. The filter may
be located at the intake device, in line with the fan, or, in
the case of a connection to the return plenum of the air
handler, using the furnace filter. An outdoor air inlet shall
be connected to either the supply or return air stream.07.3.3-2" href="#table_M1507.3.3-2" class="autolink_target">
An outdoor air inlet duct connection
to the supply air stream shall be located downstream of
the forced-air system blower. An outdoor air inlet duct
connection to the return air stream shall be located at
least 4 feet upstream of the forced-air system blower and
its filter. Neither type of duct shall be connected directly
into a furnace cabinet to prevent thermal shock to the heat
exchanger. The outdoor air inlet duct shall be
prescriptively sized in accordance with Table
M1507.3.6.2. The terminal element on the outside of the
building shall be sized 2 inches in diameter larger than
the outdoor air inlet duct.
TABLE M1507.3.6.2
PRESCRIPTIVE SUPPLY FAN DUCT SIZING
TABLE M1507.3.6.2
PRESCRIPTIVE SUPPLY FAN DUCT SIZING
| Supply Fan Tested CFM at 0.40” w.g. | ||
|---|---|---|
| Specified Volume from Table M1507.3.3(1) |
Minimum Smooth Duct Diameter |
Minimum Flexible Duct Diameter |
| 50-90 cfm | 4 inch | 5 inch |
| 90-150 cfm | 5 inch | 6 inch |
| 150-120 cfm | 6 inch | 7 inch |
| 250-400 cfm | 7 inch | 8 inch |
The system shall be equipped with
a back-draft damper and one of the following:
- A calibrated manual volume damper installed and set to meet the measured flow rates specified in Table M1507.3.3(1) by field testing with a pressure gauge and/or following manufacturer's installation instructions; or
- A manual volume damper installed and set to meet the measured flow rates specified in Table M1507.3.3(1) by field testing with a flow hood or a flow measuring station; or
- An automatic flow-regulating device sized to the specified flow rates in Table M1507.3.3(1) which provides constant flow over a pressure range of 0.20 to 0.60 inches water gauge.
Inlets shall be screened
or otherwise protected from entry by leaves or other
material. Outdoor air inlets shall be located so as not to
take air from the following areas:
- Closer than 10 feet from an appliance vent outlet, unless such vent outlet is 3 feet above the outdoor air inlet.
- Where it will pick up objectionable odors, fumes or flammable vapors.
- A hazardous or unsanitary location.
- A room or space having any fuel-burning appliances therein.
- Closer than 10 feet from a vent opening of a plumbing drainage system unless the vent opening is at least 3 feet above the air inlet.
- Attic, crawl spaces, or garages.
All
duct work in heat recovery systems shall be sized and
installed per the manufacturer's instructions. System
minimum flow rating shall be not less than that specified
in Table M1507.3.3(1). Heat recovery ventilation systems
shall have a filter on the upstream side of the heat
exchanger in both the intake and exhaust airstreams with
a minimum efficiency rating value (MERV) of 6.
Inlets shall be screened
or otherwise protected from entry by leaves or other
material. Outdoor air inlets shall be located so as not to
take air from the following areas:
- Closer than 10 feet from an appliance vent outlet, unless such vent outlet is 3 feet above the outdoor air inlet.
- Where it will pick up objectionable odors, fumes or flammable vapors.
- A hazardous or unsanitary location.
- A room or space having any fuel-burning appliances therein.
- Closer than 10 feet from a vent opening of a plumbing drainage system unless the vent opening is at least 3 feet above the air inlet.
- Attic, crawl spaces, or garages.
Local exhaust shall be provided in each kitchen, bathroom, water closet, laundry room, indoor swimming pool, spa, and other rooms where water vapor or cooking odor is produced. Local exhaust systems shall be designed to have the capacity to exhaust the minimum air flow rate determined in accordance with Table M1507.4.
TABLE M1507.4
MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
TABLE M1507.4
MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
| AREA TO BE EXHAUSTED | EXHAUST RATES |
| Kitchens | 100 cfm intermittent or 25 cfm continuous |
| Bathrooms-Toilet Rooms Laundry rooms Indoor swimming pools & spas | Mechanical exhaust capacity of 50 cfm intermittent or 20 cfm continuous |
For SI: 1 cubic foot per minute = 0.0004719 m3/s.
Exhaust fans providing
local exhaust shall have a minimum fan flow rating not less
than 50 cfm at 0.25 inches water gauge for bathrooms,
laundries, or similar rooms and 100 cfm at 0.25 inches water
gauge for kitchens. Manufacturers' fan flow ratings shall be
determined as per HVI 916 (April 1995) or AMCA 210.
Exception: Where a range hood or down draft exhaust fan
is used to satisfy the local exhaust requirements for
kitchens, the range hood or down draft exhaust shall not
be less than 100 cfm at 0.10 inches water gauge.