2113.14 Multiple flues.

When two or more flues are located in the same chimney, masonry wythes shall be built between adjacent flue linings. The masonry wythes shall be at least 4 inches (102 mm) thick and bonded into the walls of the chimney.

   Exception: When venting only one appliance, two flues are permitted to adjoin each other in the same chimney with only the flue lining separation between them. The joints of the adjacent flue linings shall be staggered not less than 4 inches (102 mm).

2113.15 Flue area (appliance).

Chimney flues shall not be smaller in area than the area of the connector from the appliance. 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.

   Exceptions:

      1.   Chimney flues serving oil-fired appliances sized in accordance with the New York City Mechanical Code and NFPA 31.

      2.   Chimney flues serving gas-fired appliances sized in accordance with the New York City Fuel Gas Code. 

2113.16 Flue area (masonry fireplace).

Flue sizing for chimneys serving fireplaces shall be in accordance with Section 2113.16.1 or 2113.16.2.

Table 2113.16(1)
Net Cross-Sectional Area of Round Flue Sizes a

Flue Size, Inside Diameter (inches)	Cross-Sectional Area (square inches)
6	28
7	38
8	50
10	78
10 3/4	90
12	113
15	176
18	254

 

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm 2

a.   Flue sizes are based on ASTM C 315.

Table 2113.16(2)
Net Cross-Sectional Area of Square and Rectangular Flue Sizes a

Flue Size, Outside Nominal Dimensions (inches)	Cross-Sectional Area (square inches)
4.5 × 8.5	23
4.5 × 13	34
8 × 8	42
8.5 × 8.5	49
8 × 12	67
8.5 × 13	76
12 × 12	102
8.5 × 18	101
13 × 13	127
12 × 16	131
13 × 18	173
16 × 16	181
16 × 20	222
18 × 18	233
20 × 20	298
20 × 24	335
24 × 24	431

 

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm 2

a.   Flue sizes are based on ASTM C 315.

For SI: 1 inch = 25.4 mm, 1 square inch = 645 mm 2 .

Figure 2113.16
Flue Sizes for Masonry Chimneys

2113.16.1 Minimum area.

Round chimney flues shall have a minimum net cross-sectional area of not less than 1/12 of the fireplace opening. Square chimney flues shall have a minimum net cross-sectional area of not less than 1/10 of the fireplace opening. Rectangular chimney flues with an aspect ratio less than 2 to 1 shall have a minimum net cross-sectional area of not less than 1/10 of the fireplace opening. Rectangular chimney flues with an aspect ratio of 2 to 1 or more shall have a minimum net cross-sectional area of not less than 1/8 of the fireplace opening.

2113.16.2 Determination of minimum area.

The minimum net cross-sectional area of the flue shall be determined in accordance with Figure 2113.16. A flue size providing not less than the equivalent net cross-sectional area shall be used. Cross-sectional areas of clay flue linings are as provided in Tables 2113.16(1) and 2113.16(2) or as provided by the manufacturer or as measured in the field. The height of the chimney shall be measured from the firebox floor to the top of the chimney flue.

2113.17 Inlet.

Inlets to masonry chimneys shall enter from the side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of the inlet or from extending beyond the wall of the liner.

2113.18 Masonry chimney cleanout openings.

Cleanout openings shall be provided within 6 inches (152 mm) of the base of each flue within every masonry chimney. The upper edge of the cleanout shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The height of the opening shall be not less than 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.

   Exception: Chimney flues serving masonry fireplaces, where cleaning is possible through the fireplace opening.

2113.19 Chimney clearances.

Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be filled, except to provide fireblocking in accordance with Section 2113.20.

   Exceptions:

      1.   Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777 and ULC-S635, and installed in accordance with the manufacturer's instructions, are permitted to have combustible material in contact with their exterior surfaces.

      2.   Where masonry chimneys are constructed as part of masonry walls, combustible materials shall not be in contact with the masonry wall less than 12 inches (305 mm) from the inside surface of the nearest flue lining.

      3.   Exposed combustible trim and the edges of sheathing materials, such as wood siding, are permitted to abut the masonry chimney sidewalls, in accordance with Figure 2113.19, provided such combustible trim or sheathing is not less than 12 inches (305 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm).

Figure 2113.19
Illustration of Exception to Chimney Clearance Provision

2113.19.1 Additional requirements for clearance.

   1.   Trimmers shall be not less than 5 inches (127 mm) from the inside face of the concrete or masonry chimney wall. Finished flooring shall have at least one-half inch clearance from chimney walls.

   2.   A clearance of at least 2 inches (51 mm) shall be provided between the exterior surfaces of interior masonry chimneys for all wood- burning appliances.

   3.   No combustible lathing, furring, or plaster grounds shall be placed against a chimney at any point more than 1 1/2 inches (38 mm) from the corner of the chimney; but this shall not prevent plastering directly on masonry or on metal lath and metal furring nor shall it prevent placing chimneys for low temperature equipment entirely on the exterior of a building against the sheathing.

2113.20 Chimney fireblocking.

All spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.