Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 of an inch (0.7722 mm) thick or of other approved, noncombustible, corrosion-resistant material. [NFPA 54:12.8.1]
Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99 percent winter design temperature is below 32°F (0°C). [NFPA 54:12.8.2]
The termination of single-wall metal pipe shall comply with the following requirements:
- Single-wall metal pipe shall terminate not less than 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood outlet or flue collar.
- Single-wall metal pipe shall extend not less than 2 feet (610 mm) above the highest point where it passes through a roof of a building and not less than 2 feet (610 mm) exceeding a portion of a building within a horizontal distance of 10 feet (3048 mm). (See Figure 802.5.4)
- An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe. [NFPA 54:12.8.3]
Single-wall metal pipe shall not be used as a vent in dwellings and residential occupancies. [NFPA 54:22.214.171.124]
Single-wall metal pipe shall be used for runs directly from the space in which the appliance is located through the roof or exterior wall to the outer air. A pipe passing through a roof shall extend without interruption through the roof flashing, roof jacket, or roof thimble. [NFPA 54:126.96.36.199]
Single-wall metal pipe shall not originate in an unoccupied attic or concealed space and shall not pass through an attic, inside wall, concealed space, or floor. [NFPA 54:188.8.131.52]
Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have required clearances maintained.
Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 802.7.3.4. Reduced clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors in Table 303.10.1. [NFPA 54:184.108.40.206]
For SI units: 1 inch = 25.4 mm
|MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches)|
|APPLIANCE||LISTED TYPE B
GAS VENT MATERIAL
|LISTED TYPE L
|Listed appliance with draft hoods and appliance listed for use with Type B gas vents||As listed||As listed||6||As listed|
|Residential boilers and furnaces with listed gas
conversion burner and with draft hood
|Residential appliances listed for use with Type L vents||Not permitted||As listed||9||As listed|
|Listed gas-fired toilets||Not permitted||As listed||As listed||As listed|
|Unlisted residential appliances with draft hood||Not permitted||6||9||As listed|
|Residential and low-heat appliance other than those
|Not permitted||9||18||As listed|
|Medium-heat appliance||Not permitted||Not permitted||36||As listed|
* These clearances shall apply unless the installation instructions of a listed appliance or connector specify different clearances, in which case the listed clearances shall apply.
A single-wall metal pipe shall not pass through a combustible exterior wall unless guarded at the point of passage by a ventilated metal thimble not smaller than the following:
- For listed appliances with draft hoods and appliances listed for use with Type B gas vents, the thimble shall be not less than 4 inches (102 mm) larger in diameter than the metal pipe. Where there is a run of not less than 6 feet (1829 mm) of metal pipe in the opening between the draft hood outlet and the thimble, the thimble shall be not less than 2 inches (51 mm) larger in diameter than the metal pipe.
- For unlisted appliances having draft hoods, the thimble shall be not less than 6 inches (152 mm) larger in diameter than the metal pipe.
- For residential and low-heat appliances, the thimble shall be not less than 12 inches (305 mm) larger in diameter than the metal pipe.
Where a single-wall metal pipe passes through a roof constructed of combustible material, a noncombustible, nonventilating thimble shall be used at the point of passage. The thimble shall extend not less than 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed at the top. The thimble shall be sized in accordance with Section 802.7.3.5. [NFPA 54:220.127.116.11]
A venting system of a single-wall metal pipe shall be sized in accordance with one of the following methods and the appliance manufacturer's instructions:
- For a draft hood-equipped appliance, in accordance with Section 803.0.
- For a venting system for a single appliance with a draft hood, the areas of the connector and the pipe each shall not be less than the area of the appliance flue collar or draft hood outlet, whichever is smaller. The vent area shall not exceed seven times the draft hood outlet area.
- Other approved engineering methods. [NFPA 54:12.8.5(1)]
Where a single-wall metal pipe is used and has a shape other than round, it shall have an effective area equal to the effective area of the round pipe for which it is substituted, and the internal dimension of the pipe shall be not less than 2 inches (51 mm). [NFPA 54:12.8.5(2)]
The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached. [NFPA 54:12.8.5(3)]
Portions of single-wall metal pipe shall be supported for the design and weight of the material employed. [NFPA 54:12.8.6]