User notes:
About this chapter: Chapter 18 addresses chimneys and vents that serve oil- and solid fuel-fired appliances, including wood pellet appliances. Gas-fired appliances are vented in accordance with Chapter 24. Chapter 10 addresses chimneys for fireplaces and masonry and factory-built chimneys in general. Note that chimneys and vents are distinct.
Code development reminder: Code change proposals to this chapter will be considered by the IRC—Plumbing/Mechanical Code Development Committee during the 2021 (Group A) Code Development Cycle.
Fuel-burning appliances shall be vented to the outdoors in accordance with their listing and label and manufacturer's installation instructions except appliances listed and labeled for unvented use. Venting systems shall consist of approved chimneys or vents, or venting assemblies that are integral parts of labeled appliances. Gas-fired appliances shall be vented in accordance with Chapter 24.
A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer's installation instructions, and shall be constructed and installed to develop a positive flow to convey combustion products to the outside atmosphere.
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 done 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 free of cracks, gaps, perforations, or other damage or deterioration that would allow the escape of combustion products, including gases, moisture and creosote.
Chimneys and vents shall have airspace clearance to combustibles in accordance with this code and the chimney or vent manufacturer's installation instructions.
Exception: Masonry chimneys equipped with a chimney lining system tested and listed for installation in chimneys in contact with combustibles in accordance with UL 1777, and installed in accordance with the manufacturer's instructions, shall not be required to have a clearance between combustible materials and exterior surfaces of the masonry chimney. Noncombustible firestopping shall be provided in accordance with this code.
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.
A mechanical draft system shall be used only with appliances listed and labeled for such use. Provisions shall be made to prevent the flow of fuel to the equipment when the draft system is not operating. Forced draft systems and portions of induced draft systems under positive pressure during operation shall be designed and installed to prevent leakage of flue gases into a building.
Direct-vent appliances shall be installed in accordance with the manufacturer's instructions.
Venting systems shall be adequately supported for the weight of the material used.
Chimneys, vents and vent connectors shall not extend into or through supply and return air ducts or plenums.
Unused openings in any venting system shall be closed or capped.
Two or more listed and labeled appliances connected to a common natural draft venting system shall comply with the following requirements:
- Appliances that are connected to common venting systems shall be located on the same floor of the dwelling.Exception: Engineered systems as provided for in Section G2427.
- Inlets to common venting systems shall be offset such that no portion of an inlet is opposite another inlet.
- Connectors serving appliances operating under a natural draft shall not be connected to any portion of a mechanical draft system operating under positive pressure.
Draft hoods shall be located in the same room or space as the combustion air openings for the appliances.
Manually operated dampers shall not be installed except in connectors or chimneys serving solid fuel-burning appliances.
Automatically operated dampers shall conform to UL 17 and be installed in accordance with the terms of their listing and label. The installation shall prevent firing of the burner when the damper is not opened to a safe position.
Draft regulators shall be provided for oil-fired appliances that must be connected to a chimney. Draft regulators provided for solid fuel-burning appliances to reduce draft intensity shall be installed and set in accordance with the manufacturer's installation instructions.
Where required, draft regulators shall be installed in the same room or enclosure as the appliance so that a difference in pressure will not exist between the air at the regulator and the combustion air supply.
Oil-fired appliances shall be equipped with a device that will stop burner operation in the event that the venting system is obstructed. Such device shall have a manual reset and shall be installed in accordance with the manufacturer's instructions.
Connectors for oil and solid fuel-burning appliances shall be constructed of factory-built chimney material, Type L vent material or single-wall metal pipe having resistance to corrosion and heat and thickness not less than that of galvanized steel as specified in Table M1803.2.
TABLE M1803.2
THICKNESS FOR SINGLE-WALL METAL PIPE CONNECTORS| DIAMETER OF CONNECTOR (inches) |
GALVANIZED SHEET METAL GAGE NUMBER | MINIMUM THICKNESS (inch) |
| Less than 6 | 26 | 0.019 |
| 6 to 10 | 24 | 0.024 |
| Over 10 through 16 | 22 | 0.029 |
For SI: 1 inch = 25.4 mm.
Vent and chimney connectors shall be installed in accordance with the manufacturer's instructions and within the space where the appliance is located. Appliances shall be located as close as practical to the vent or chimney. Connectors shall be as short and straight as possible and installed with a slope of not less than 1/4 inch (6 mm) rise per foot of run. Connectors shall be securely supported and joints shall be fastened with sheet metal screws or rivets. Devices that obstruct the flow of flue gases shall not be installed in a connector unless listed and labeled or approved for such installation.
A chimney connector or vent connector shall not pass through any floor or ceiling. A chimney connector or vent connector shall not pass through a wall or partition unless the connector is listed and labeled for wall pass-through, or is routed through a device listed and labeled for wall pass-through and is installed in accordance with the conditions of its listing and label. Connectors for oil-fired appliances listed and labeled for Type L vents, passing through walls or partitions shall be in accordance with the following:
- Type L vent material for oil appliances shall be installed with not less than listed and labeled clearances to combustible material.
- Single-wall metal pipe shall be guarded by a ventilated metal thimble not less than 4 inches (102 mm) larger in diameter than the vent connector. Not less than 6 inches (152 mm) of clearance shall be maintained between the thimble and combustibles.
The horizontal run of an uninsulated connector to a natural draft chimney shall not exceed 75 percent of the height of the vertical portion of the chimney above the connector. The horizontal run of a listed connector to a natural draft chimney shall not exceed 100 percent of the height of the vertical portion of the chimney above the connector.
A connector shall not be smaller than the flue collar of the appliance.
Exception: Where installed in accordance with the appliance manufacturer's instructions.
Connectors shall be installed with clearance to combustibles as set forth in Table M1803.3.4. Reduced clearances to combustible materials shall be in accordance with Table M1306.2 and Figure M1306.1.
| TYPE OF CONNECTOR | MINIMUM CLEARANCE (inches) |
| Single-wall metal pipe connectors: | |
|
Oil and solid-fuel appliances
|
18 |
| 9 | |
| Type L vent piping connectors: | |
|
Oil and solid-fuel appliances
|
9 |
| 3b | |
For SI: 1 inch = 25.4 mm.
- These minimum clearances apply to unlisted single-wall chimney and vent connectors. Reduction of required clearances is permitted as in Table M1306.2.
- Where listed Type L vent piping is used, the clearance shall be in accordance with the vent listing.
The entire length of a connector shall allow access for inspection, cleaning and replacement.
Connection of appliances to chimney flues serving fireplaces shall comply with Sections M1803.4.1 through M1803.4.4.
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.
A different appliance shall not be connected to a flue serving a factory-built fireplace unless the appliance is specifically listed for such an installation. The connection shall be made in compliance with the appliance manufacturer's instructions.
A connector shall extend from the appliance to the flue serving a masonry fireplace to convey the flue gases 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.
The size of the fireplace flue shall be in accordance with Section M1805.3.1.
Appliances shall be provided with a listed and labeled venting system as set forth in Table M1804.1.
TABLE M1804.1
VENT SELECTION CHART| VENT TYPES | APPLIANCE TYPES |
| Type L oil vents | Oil-burning appliances listed and labeled for venting with Type L vents |
| Pellet vents | Pellet fuel-burning appliances listed and labeled for use with pellet vents |
Vents passing through a roof shall extend through flashing and terminate in accordance with the manufacturer's installation requirements.
Decorative shrouds shall not be installed at the termination of vents except where the shrouds are listed and labeled for use with the specific venting system and are installed in accordance with the manufacturer's instructions.
Vents for natural draft appliances shall terminate not less than 5 feet (1524 mm) above the highest connected appliance outlet, and natural draft gas vents serving wall furnaces shall terminate at an elevation not less than 12 feet (3658 mm) above the bottom of the furnace.
Type L venting systems shall conform to UL 641 and shall terminate with a listed and labeled cap in accordance with the vent manufacturer's installation instructions not less than 2 feet (610 mm) above the roof and not less than 2 feet (610 mm) above any portion of the building within 10 feet (3048 mm).
Vent terminals for direct-vent appliances shall be installed in accordance with the manufacturer's instructions.
Mechanical draft systems shall comply with UL 378 and shall be installed in accordance with their listing, the manufacturer's instructions and, except for direct-vent appliances, the following requirements:
- The vent terminal shall be located not less than 3 feet (914 mm) above a forced air inlet located within 10 feet (3048 mm).
- The vent terminal shall be located not less than 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 a dwelling.
- The vent termination point shall be located not closer than 3 feet (914 mm) to an interior corner formed by two walls perpendicular to each other.
- The bottom of the vent terminal shall be located not less than 12 inches (305 mm) above finished ground level.
- The vent termination shall not be mounted directly above or within 3 feet (914 mm) horizontally of an oil tank vent or gas meter.
- Power exhauster terminations shall be located not less than 10 feet (3048 mm) from lot lines and adjacent buildings.
- The discharge shall be directed away from the building.
Upcodes Diagrams
Type L and pellet vents shall be installed in accordance with the terms of their listing and label and the manufacturer's instructions.
Masonry and factory-built chimneys shall be built and installed in accordance with Sections R1003 and R1005, respectively. Flue lining for masonry chimneys shall comply with Section R1003.11.
A chimney connector shall enter a masonry chimney not less than 6 inches (152 mm) above the bottom of the chimney. Where it is not possible to locate the connector entry not less than 6 inches (152 mm) above the bottom of the chimney flue, a cleanout shall be provided by installing a capped tee in the connector next to the chimney. A connector entering a masonry chimney shall extend through, but not beyond, the wall and shall be flush with the inner face of the liner. Connectors, or thimbles where used, shall be firmly cemented into the masonry.
The effective area of a natural draft chimney flue for one appliance shall be not less than the area of the connector to the appliance. The area of chimney flues connected to more than one appliance shall be not less than the area of the largest connector plus 50 percent of the areas of additional chimney connectors.
Except where otherwise specified in the manufacturer's installation instructions, the cross-sectional area of a flue connected to a solid fuel-burning appliance shall be not less than the area of the flue collar or connector, and not larger than three times the area of the flue collar.