2113.11.3.4 Clearance.

Masonry chimneys for high-heat appliances shall have approved clearance from buildings and structures to prevent overheating combustible materials, permit inspection and maintenance operations on the chimney and prevent danger of burns to persons.

2113.12 Clay flue lining (installation).

Flue liners shall be installed in accordance with ASTM C 1283 and extend from a point not less than 8 inches (203 mm) below the lowest inlet or, in the case of fireplaces, from the top of the smoke chamber to a point above the enclosing walls. The lining shall be carried up vertically, with a maximum slope no greater than 30 degrees (0.52 rad) from the vertical.

Clay flue liners shall be laid in medium-duty nonwater-soluble refractory mortar conforming to ASTM C 199 with tight mortar joints left smooth on the inside and installed to maintain an airspace or insulation not to exceed the thickness of the flue liner separating the flue liners from the interior face of the chimney masonry walls. Flue lining shall be supported on all sides. Only enough mortar shall be placed to make the joint and hold the liners in position.

2113.13 Additional requirements.

Masonry chimneys shall also comply with the additional requirements of Sections 2113.13.1 and 2113.13.2.

2113.13.1 Listed materials.

Listed materials used as flue linings shall be installed in accordance with the terms of their listings and the manufacturer's instructions.

2113.13.2 Space around lining.

The space surrounding a chimney lining system or vent installed within a masonry chimney shall not be used to vent any other appliance.

   Exception: This shall not prevent the installation of a separate flue lining in accordance with the manufacturer's instructions.

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.