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. See explanation on page iv.


    M1801.1 Venting required.

    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.

    M1801.2 Draft requirements.

    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.

    M1801.3 Existing chimneys and vents.

    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 M1801.3.1 through M1801.3.4.

    M1801.3.1 Size.

    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.

    M1801.3.2 Flue passageways.

    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.

    M1801.3.3 Cleanout.

    Masonry chimneys shall be provided with a cleanout opening complying with Section R1003.17.

    M1801.3.4 Clearances.

    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.

    M1801.4 Space around lining.

    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.

    M1801.5 Mechanical draft systems.

    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.

    M1801.6 Direct-vent appliances.

    Direct-vent appliances shall be installed in accordance with the manufacturer’s instructions.

    M1801.7 Support.

    Venting systems shall be adequately supported for the weight of the material used.

    M1801.8 Duct penetrations.

    Chimneys, vents and vent connectors shall not extend into or through supply and return air ducts or plenums.

    M1801.9 Fireblocking.

    Vent and chimney installations shall be fireblocked in accordance with Section R602.8.

    M1801.10 Unused openings.

    Unused openings in any venting system shall be closed or capped.

    M1801.11 Multiple-appliance venting systems.

    Two or more listed and labeled appliances connected to a common natural draft venting system shall comply with the following requirements:

    1. 1.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.

    2. 2.Inlets to common venting systems shall be offset such that no portion of an inlet is opposite another inlet.

    3. 3.Connectors serving appliances operating under a natural draft shall not be connected to any portion of a mechanical draft system operating under positive pressure.

    M1801.12 Multiple solid fuel prohibited.

    A solid fuel-burning appliance or fireplace shall not connect to a chimney passageway venting another appliance.