CODES

ADOPTS WITH AMENDMENTS:

International Mechanical Code 2012 (IMC 2012)

Copyright

Preface

Chapter 1 Administration

Chapter 2 Definitions

Chapter 3 General Regulations

Chapter 4 Ventilation

Chapter 5 Exhaust Systems

Chapter 6 Duct Systems

Chapter 7 Combustion Air

Chapter 8 Chimneys and Vents

Chapter 9 Specific Appliances, Fireplaces and Solid Fuel-Burning Equipment

Chapter 10 Boilers, Water Heaters and Pressure Vessels

Chapter 11 Refrigeration

Chapter 12 Hydronic Piping

Chapter 13 Fuel Oil Piping and Storage

Chapter 14 Solar Systems

Chapter 15 Referenced Standards

Appendix A Chimney Connector Pass-Throughs

Appendix B Recommended Permit Fee Schedule

This chapter shall govern the installation, maintenance, repair and approval of factory-built chimneys, chimney liners, vents and connectors. This chapter shall also govern the utilization of masonry chimneys. Gas-fired appliances shall be vented in accordance with the International Fuel Gas Code.

Every fuel-burning appliance shall discharge the products of combustion to a vent, factory-built chimney or masonry chimney, except for appliances vented in accordance with Section 804. The chimney or vent shall be designed for the type of appliance being vented.

Exception: Commercial cooking appliances vented by a Type I hood installed in accordance with Section 507.

Oil-fired appliances shall be vented in accordance with this code and NFPA 31.
Masonry chimneys shall be constructed in accordance with the International Building Code.
Venting systems shall be designed and constructed so as to develop a positive flow adequate to convey all combustion products to the outside atmosphere.
Venting systems shall be designed in accordance with this chapter or shall be approved engineered systems.
Except as otherwise provided for in this chapter, the size of the chimney or vent, serving a single appliance, except engineered systems, shall have a minimum area equal to the area of the appliance connection.
The cross-sectional area of a flue serving a solid-fuel-burning appliance shall be not greater than three times the cross-sectional area of the appliance flue collar or flue outlet.
Abandoned inlet openings in chimneys and vents shall be closed by an approved method.
Where an appliance equipped with a forced or induced draft system creates a positive pressure in the venting system, the venting system shall be designed and listed for positive pressure applications.
Connection of appliances to chimney flues serving fireplaces shall be in accordance with Sections 801.10.1 through 801.10.3.
A noncombustible seal shall be provided below the point of connection to prevent entry of room air into the flue. Means shall be provided for access to the flue for inspection and cleaning.
An appliance shall not be connected to a flue serving a factory-built fireplace unless the appliance is specifically listed for such installation. The connection shall be made in accordance with the appliance manufacturer’s installation instructions.
A connector shall extend from the appliance to the flue serving a masonry fireplace such that the flue gases are exhausted directly into the flue. The connector shall be provided with access or shall be removable for inspection and cleaning of both the connector and the flue. Listed direct connection devices shall be installed in accordance with their listing.
A solid fuel-burning appliance or fireplace shall not connect to a chimney passageway venting another appliance.
Connectors shall connect to a chimney flue at a point not less than 12 inches (305 mm) above the lowest portion of the interior of the chimney flue.

Masonry chimney flues shall be provided with a cleanout opening having a minimum height of 6 inches (152 mm). The upper edge of the opening shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The cleanout shall be provided with a tight-fitting, noncombustible cover.

Exception: Cleanouts shall not be required for chimney flues serving masonry fireplaces, if such flues are provided with access through the fireplace opening.

All appliance connections to a chimney or vent equipped with a power exhauster shall be made on the inlet side of the exhauster. All joints and piping on the positive pressure side of the exhauster shall be listed for positive pressure applications as specified by the manufacturer’s installation instructions for the exhauster.
Masonry chimneys utilized to vent fuel-fired appliances shall be located, constructed and sized as specified in the manufacture’s installation instructions for the appliances being vented.
Masonry chimneys shall be lined. The lining material shall be compatible with the type of appliance connected, in accordance with the appliance listing and manufacturer’s installation instructions. Listed materials used as flue linings shall be installed in accordance with their listings and the manufacturer’s installation instructions.

Flue lining systems for use with residential-type and low-heat appliances shall be limited to the following:

  1. Clay flue lining complying with the requirements of ASTM C 315 or equivalent. Clay flue lining shall be installed in accordance with the International Building Code.
  2. Listed and labeled chimney lining systems complying with UL 1777.
  3. Other approved materials that will resist, without cracking, softening or corrosion, flue gases and condensate at temperatures up to 1,800°F (982°C).
The space surrounding a flue lining system or other vent installed within a masonry chimney shall not be used to vent any other appliance. This shall not prevent the installation of a separate flue lining in accordance with the manufacturer’s installation instructions and this code.
Where an appliance is permanently disconnected from an existing chimney or vent, or where an appliance is connected to an existing chimney or vent during the process of a new installation, the chimney or vent shall comply with Sections 801.18.1 through 801.18.4.
The chimney or vent shall be resized as necessary to control flue gas condensation in the interior of the chimney or vent and to provide the appliance or appliances served with the required draft. For the venting of oil-fired appliances to masonry chimneys, the resizing shall be in accordance with NFPA 31.
The flue gas passageway shall be free of obstructions and combustible deposits and shall be cleaned if previously used for venting a solid or liquid fuel-burning appliance or fireplace. The flue liner, chimney inner wall or vent inner wall shall be continuous and shall be free of cracks, gaps, perforations or other damage or deterioration which would allow the escape of combustion products, including gases, moisture and creosote. Where an oil-fired appliance is connected to an existing masonry chimney, such chimney flue shall be repaired or relined in accordance with NFPA 31.
Masonry chimneys shall be provided with a cleanout opening complying with Section 801.13.

Chimneys and vents shall have airspace clearance to combustibles in accordance with the International Building Code and the chimney or vent manufacturer’s installation instructions.

Exception: Masonry chimneys without the required airspace clearances shall be permitted to be used if lined or relined with a chimney lining system listed for use in chimneys with reduced clearances in accordance with UL 1777. The chimney clearance shall be not less than permitted by the terms of the chimney liner listing and the manufacturer’s instructions.

Noncombustible fireblocking shall be provided in accordance with the International Building Code.
Common venting systems for appliances located on more than one floor level shall be prohibited, except where all of the appliances served by the common vent are located in rooms or spaces that are accessed only from the outdoors. The appliance enclosures shall not communicate with the occupiable areas of the building.

Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions.

All vent systems shall be listed and labeled. Type L vents and pellet vents shall be tested in accordance with UL 641.

The application of vents shall be in accordance with Table 802.2.

TABLE 802.2

VENT APPLICATION

VENT TYPESAPPLIANCE TYPES
Type L oil ventsOil-burning appliances listed and labeled for
venting with Type L vents; gas appliances listed
and labeled for venting with Type B vents.
Pellet ventsPellet fuel-burning appliances listed and labeled
for venting with pellet vents.
Vent systems shall be sized, installed and terminated in accordance with the vent and appliance manufacturer’s installation instructions.
Type L vents shall terminate with a listed and labeled cap in accordance with the vent manufacturer’s installation instructions.
Type L vents shall terminate not less than 2 feet (610 mm) above the highest point of the roof penetration and not less than 2 feet (610 mm) higher than any portion of a building within 10 feet (3048 mm).

Vents shall terminate not less than 5 feet (1524 mm) in vertical height above the highest connected appliance flue collar.

Exceptions:

  1. Venting systems of direct vent appliances shall be installed in accordance with the appliance and the vent manufacturer’s instructions.
  2. Appliances listed for outdoor installations incorporating integral venting means shall be installed in accordance with their listings and the manufacturer’s installation instructions.
  3. Pellet vents shall be installed in accordance with the appliance and the vent manufacturer’s installation instructions.
All portions of vents shall be adequately supported for the design and weight of the materials employed.
Where vents pass through insulated assemblies, an insulation shield constructed of not less than No. 26 gage sheet metal shall be installed to provide clearance between the vent and the insulation material. The clearance shall be not less than the clearance to combustibles specified by the vent manufacturer’s installation instructions. Where vents pass through attic space, the shield shall terminate not less than 2 inches (51 mm) above the insulation materials and shall be secured in place to prevent displacement. Insulation shields provided as part of a listed vent system shall be installed in accordance with the manufacturer’s installation instructions.
Connectors shall be used to connect appliances to the vertical chimney or vent, except where the chimney or vent is attached directly to the appliance.
Connectors shall be located entirely within the room in which the connecting appliance is located, except as provided for in Section 803.10.4. Where passing through an unheated space, a connector shall not be constructed of single-wall pipe.
The connector shall not be smaller than the size of the flue collar supplied by the manufacturer of the appliance. Where the appliance has more than one flue outlet, and in the absence of the manufacturer’s specific instructions, the connector area shall be not less than the combined area of the flue outlets for which it acts as a common connector.
All branch connections to the vent connector shall be made in accordance with the vent manufacturer’s instructions.
Manual dampers shall not be installed in connectors except in chimney connectors serving solid fuel-burning appliances.
Automatic dampers shall be listed and labeled in accordance with UL 17 for oil-fired heating appliances. The dampers shall be installed in accordance with the manufacturer’s installation instructions. An automatic vent damper device shall not be installed on an existing appliance unless the appliance is listed and labeled and the device is installed in accordance with the terms of its listing. The name of the installer and date of installation shall be marked on a label affixed to the damper device.
Where two or more connectors enter a common vent or chimney, the smaller connector shall enter at the highest level consistent with available headroom or clearance to combustible material.
Vent connectors shall be constructed of metal. The minimum thickness of the connector shall be 0.0136 inch (0.345 mm) (No. 28 gage) for galvanized steel, 0.022 inch (0.6 mm) (No. 26 B & S gage) for copper, and 0.020 inch (0.5 mm) (No. 24 B & S gage) for aluminum.

Chimney connectors for low-heat appliances shall be of sheet steel pipe having resistance to corrosion and heat not less than that of galvanized steel specified in Table 803.9(1). Connectors for medium-heat appliances and high-heat appliances shall be of sheet steel not less than the thickness specified in Table 803.9(2).

TABLE 803.9(1)

MINIMUM CHIMNEY CONNECTOR THICKNESS FOR LOW-HEAT APPLIANCES

DIAMETER OF CONNECTOR
(inches)
MINIMUM NOMINAL THICKNESS
(galvanized) (inches)
5 and smaller0.022 (No. 26 gage)
Larger than 5 and up to 100.028 (No. 24 gage)
Larger than 10 and up to 160.034 (No. 22 gage)
Larger than 160.064 (No. 16 gage)

For SI: 1 inch = 25.4 mm.

TABLE 803.9(2)

MINIMUM CHIMNEY CONNECTOR THICKNESS FOR MEDIUM- AND HIGH-HEAT APPLIANCE

AREA
(square inches)
EQUIVALENT ROUND
DIAMETER
(inches)
MINIMUM THICKNESS
(inches)
0-1540-140.0575
(No. 16 gage)
155-20115-160.075
(No. 14 gage)
202-25417-180.0994
(No. 12 gage)
Greater than 254Greater than 180.1292
(No. 10 gage)

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2.

Connectors shall be installed in accordance with Sections 803.10.1 through 803.10.6.
Connectors shall be supported in an approved manner, and joints shall be fastened with sheet metal screws, rivets or other approved means.
The maximum horizontal length of a single-wall connector shall be 75 percent of the height of the chimney or vent.
The connector shall extend to the inner face of the chimney or vent liner, but not beyond. A connector entering a masonry chimney shall be cemented to masonry in an approved manner. Where thimbles are installed to facilitate removal of the connector from the masonry chimney, the thimble shall be permanently cemented in place with high-temperature cement.

Chimney connectors shall not pass through any floor or ceiling, nor through a fire-resistance-rated wall assembly. Chimney connectors for domestic-type appliances shall not pass through walls or partitions constructed of combustible material to reach a masonry chimney unless:

  1. The connector is labeled for wall pass-through and is installed in accordance with the manufacturer’s instructions;
  2. The connector is put through a device labeled for wall pass-through; or
  3. The connector has a diameter not larger than 10 inches (254 mm) and is installed in accordance with one of the methods in Table 803.10.4. Concealed metal parts of the pass-through system in contact with flue gases shall be of stainless steel or equivalent material that resists corrosion, softening or cracking up to 1,800°F (980°C).

TABLE 803.10.4

CHIMNEY CONNECTOR SYSTEMS AND CLEARANCES TO COMBUSTIBLE WALL MATERIALS FOR DOMESTIC HEATING APPLIANCESa, b, c, d

System A
(12-inch
clearance)
A 3.5-inch-thick brick wall shall be framed into the
combustible wall. An 0.625-inch-thick fire-clay liner
(ASTM C 315 or equivalent)e shall be firmly cemented
in the center of the brick wall maintaining a 12-inch
clearance to combustibles. The clay liner shall run
from the outer surface of the bricks to the inner surface
of the chimney liner.
System B
(9-inch
clearance)
A labeled solid-insulated factory-built chimney section
(1-inch insulation) the same inside diameter as the
connector shall be utilized. Sheet steel supports cut to
maintain a 9-inch clearance to combustibles shall be
fastened to the wall surface and to the chimney section.
Fasteners shall not penetrate the chimney flue
liner. The chimney length shall be flush with the
masonry chimney liner and sealed to the masonry with
water-insoluble refractory cement. Chimney manufacturers’
parts shall be utilized to securely fasten the
chimney connector to the chimney section.
System C
(6-inch
clearance)
A steel ventilated thimble having a minimum thickness
of 0.0236 inch (No. 24 gage) having two 1-inch
air channels shall be installed with a steel chimney
connector. Steel supports shall be cut to maintain a
6-inch clearance between the thimble and combustibles.
The chimney connector and steel supports shall have a
minimum thickness of 0.0236 inch (No. 24 gage). One
side of the support shall be fastened to the wall on all sides.
Glass-fiber insulation shall fill the 6-inch space
between the thimble and the supports.
System D
(2-inch
clearance)
A labeled solid-insulated factory-built chimney section
(1-inch insulation) with a diameter 2 inches larger than
the chimney connector shall be installed with a steel
chimney connector having a minimum thickness of
0.0236 inch (24 gage). Sheet steel supports shall be
positioned to maintain a 2-inch clearance to combustibles
and to hold the chimney connector to ensure that a
1-inch airspace surrounds the chimney connector
through the chimney section. The steel support shall be
fastened to the wall on all sides and the chimney section
shall be fastened to the supports. Fasteners shall
not penetrate the liner of the chimney section.

For SI: 1 inch = 25.4 mm, 1.0 Btu × in/ft2 • h • °F = 0.144 W/m2 • K.

  1. Insulation material that is part of the wall pass-through system shall be noncombustible and shall have a thermal conductivity of 1.0 Btu × in/ft2 • h • °F or less.
  2. All clearances and thicknesses are minimums.
  3. Materials utilized to seal penetrations for the connector shall be noncombustible.
  4. Connectors for all systems except System B shall extend through the wall pass-through system to the inner face of the flue liner.
  5. ASTM C 315.
Connectors shall rise vertically to the chimney or vent with a minimum pitch equal to one-fourth unit vertical in 12 units horizontal (2-percent slope).

Connectors shall have a minimum clearance to combustibles in accordance with Table 803.10.6. The clearances specified in Table 803.10.6 apply, except where the listing and labeling of an appliance specifies a different clearance, in which case the labeled clearance shall apply. The clearance to combustibles for connectors shall be reduced only in accordance with Section 308.

TABLE 803.10.6

CONNECTOR CLEARANCES TO COMBUSTIBLES

TYPE OF APPLIANCEMINIMUM CLEARANCE
(inches)
Domestic-type appliances
Chimney and vent connectors
Electric and oil incinerators18
Oil and solid-fuel appliances18
Oil appliances labeled for venting
with Type L vents
9
Commercial, industrial-type appliances
Low-heat appliances
Chimney connectors
Oil and solid-fuel boilers, furnace
and water heaters
18
Oil unit heaters18
Other low-heat industrial appliances18
Medium-heat appliances
Chimney connectors
All oil and solid-fuel appliances36
High-heat appliances
Masonry or metal connectors
All oil and solid-fuel appliances
(As determined by the
code official)

For SI: 1 inch = 25.4 mm.

Vent terminals for direct-vent appliances shall be installed in accordance with the manufacturer’s installation instructions.
Appliances incorporating integral venting means shall be installed in accordance with their listings and the manufacturer’s installation instructions.
Appliances designed for natural draft venting and incorporating integral venting means shall be located so that a minimum clearance of 9 inches (229 mm) is maintained between vent terminals and from any openings through which combustion products enter the building. Appliances using forced draft venting shall be located so that a minimum clearance of 12 inches (305 mm) is maintained between vent terminals and from any openings through which combustion products enter the building.
Mechanical draft systems of either forced or induced draft design shall be listed and labeled in accordance with UL 378 and shall comply with Sections 804.3.1 through 804.3.7.
Forced draft systems and all portions of induced draft systems under positive pressure during operation shall be designed and installed so as to be gas tight to prevent leakage of combustion products into a building.
Power exhausters serving automatically fired appliances shall be electrically connected to each appliance to prevent operation of the appliance when the power exhauster is not in operation.
The termination of chimneys or vents equipped with power exhausters shall be located a minimum of 10 feet (3048 mm) from the lot line or from adjacent buildings. The exhaust shall be directed away from the building.

Horizontal terminations shall comply with the following requirements:

  1. Where located adjacent to walkways, the termination of mechanical draft systems shall be not less than 7 feet (2134 mm) above the level of the walk-way.
  2. Vents shall terminate at least 3 feet (914 mm) above any forced air inlet located within 10 feet (3048 mm).
  3. The vent system shall terminate at least 4 feet (1219 mm) below, 4 feet (1219 mm) horizontally from or 1 foot (305 mm) above any door, window or gravity air inlet into the building.
  4. The vent termination point shall not be located closer than 3 feet (914 mm) to an interior corner formed by two walls perpendicular to each other.
  5. The vent termination shall not be mounted directly above or within 3 feet (914 mm) horizontally from an oil tank vent or gas meter.
  6. The bottom of the vent termination shall be located at least 12 inches (305 mm) above finished grade.

Vertical terminations shall comply with the following requirements:

  1. Where located adjacent to walkways, the termination of mechanical draft systems shall be not less than 7 feet (2134 mm) above the level of the walk-way.
  2. Vents shall terminate at least 3 feet (914 mm) above any forced air inlet located within 10 feet (3048 mm) horizontally.
  3. Where the vent termination is located below an adjacent roof structure, the termination point shall be located at least 3 feet (914 mm) from such structure.
  4. The vent shall terminate at least 4 feet (1219 mm) below, 4 feet (1219 mm) horizontally from or 1 foot (305 mm) above any door, window or gravity air inlet for the building.
  5. A vent cap shall be installed to prevent rain from entering the vent system.
  6. The vent termination shall be located at least 3 feet (914 mm) horizontally from any portion of the roof structure.
An appliance vented by natural draft shall not be connected into a vent, chimney or vent connector on the discharge side of a mechanical flue exhauster.
Mechanical flue exhausters and the vent system served shall be sized and installed in accordance with the manufacturer’s installation instructions.

A mechanical draft system shall be permitted to be used with manually fired appliances and fireplaces where such system complies with all of the following requirements:

  1. The mechanical draft device shall be listed and labeled in accordance with UL 378, and shall be installed in accordance with the manufacturer’s instructions.
  2. A device shall be installed that produces visible and audible warning upon failure of the mechanical draft device or loss of electrical power, at any time that the mechanical draft device is turned on. This device shall be equipped with a battery backup if it receives power from the building wiring.
  3. A smoke detector shall be installed in the room with the appliance or fireplace. This device shall be equipped with a battery backup if it receives power from the building wiring.
Factory-built chimneys shall be listed and labeled and shall be installed and terminated in accordance with the manufacturer’s installation instructions.

Factory-built chimneys installed in dwelling units with solid fuel-burning appliances shall comply with the Type HT requirements of UL 103 and shall be marked “Type HT” and “Residential Type and Building Heating Appliance Chimney.”

Exception: Chimneys for use with open combustion chamber fireplaces shall comply with the requirements of UL 103 and shall be marked “Residential Type and Building Heating Appliance Chimney.”

Chimneys for use with open combustion chamber appliances installed in buildings other than dwelling units shall comply with the requirements of UL 103 and shall be marked “Building Heating Appliance Chimney” or “Residential Type and Building Heating Appliance Chimney.”

Where a factory-built chimney assembly incorporates offsets, no part of the chimney shall be at an angle of more than 30 degrees (0.52 rad) from vertical at any point in the assembly and the chimney assembly shall not include more than four elbows.
Chimneys for factory-built fireplaces shall comply with the requirements of UL 127.
Where factory-built chimneys are supported by structural members, such as joists and rafters, such members shall be designed to support the additional load.
Factory-built chimneys for medium-heat appliances producing flue gases having a temperature above 1,000°F (538°C), measured at the entrance to the chimney, shall comply with UL 959.
Decorative shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are listed and labeled for use with the specific factory-built chimney system and are installed in accordance with Section 304.1.
Metal chimneys shall be constructed and installed in accordance with NFPA 211.
Resources