Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 21 - Masonry
Section 2113 - MASONRY CHIMNEYS
Subsection 2113.16 - Flue area (masonry fireplace)

Universal Citation: 780 CMR MA Code of Regs 2113.16

Current through Register 1531, September 27, 2024

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 SIZESa

FLUE SIZE, INSIDE DIAMETER
(inches) 		CROSS-SECTIONAL AREA
(square inches)
6 28
7 38
8 50
10 78
103/4 90
12 113
15 176
18 254

For SI: 1 inch = 25.4 mm, 1 square inch = 645 mm2.
a. Flue sizes are based on ASTM C 315.

TABLE 2113.16(2) NET CROSS-SECTIONAL AREA OF SQUARE AND RECTANGULAR FLUE SIZES

FLUE SIZE, OUTSIDE NOMINAL DIMENSIONS
(inches) 		CROSS-SECTIONAL AREA
(square inches)
4.5 x 8.5 23
4.5 x 13 34
8 x 8 42
8.5 x 8.5 49
8 x 12 67
8.5 x 13 76
12 x 12 102
8.5 x 18 101
13 x 13 127
12 x 16 131
13 x 18 173
16 x 16 181
16 x 20 222
18 x 18 233
20 x 20 298
20 x 24 335
24 x 24 431

For SI: 1 inch = 25.4 mm, 1 square inch = 645 mm2.

For SI: 1 foot = 304.8 mm, 1 square inch = 645 mm2.

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 at least 1/12 of the fireplace opening. Square chimney flues shall have a minimum net cross-sectional area of at least 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 at least 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 at least 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 at least 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.

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