Chimney Damper Opening Area
NYC Fuel Gas Code § FGC 634
in effectSection FGC 634: Chimney Damper Opening Area
634.1 Free opening area of chimney dampers.
Where an unlisted decorative appliance for installation in a vented fireplace is installed, the fireplace damper shall have a permanent free opening equal to or greater than specified in Table 634.1.
Table 634.1
Free Opening Area of Chimney Damper for Venting Flue Gasses from Unlisted Decorative Appliances for Installation in Vented Fireplaces
Chimney Height (Feet) Minimum Permanent Free Opening (Square Inches) a
8 13 20 29 39 51 64
Appliance Input Rating (BTU Per Hour)
6 7,800 14,000 23,200 34,000 46,400 62,400 8,000
8 8,400 15,200 25,200 37,000 50,400 68,000 86,000
10 9,000 16,800 27,600 40,400 55,800 74,400 96,400
15 9,800 18,200 30,200 44,600 62,400 84,000 108,800
20 10,600 20,200 32,600 50,400 68,400 94,000 122,200
30 11,200 21,600 36,600 55,200 76,800 105,800 138,600
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 square inch = 645.16 m2, 1 British thermal unit per hour = 0.2931 W.
a. The first six minimum permanent free openings (8 to 51 square inches) correspond approximately to the cross-sectional areas of chimneys having diameters of 3 through 8 inches, respectively. The 64-square-inch opening corresponds to the cross-sectional area of standard 8-inch by 8-inch chimney tile.
Source: City of New York, Charter, Administrative Code and Rules (American Legal Publishing XML export, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/newyorkcity/latest/NYCadmin/0-0-0-199445Fetched: 10/24/2026