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DUCT SYSTEM QUICK SIZING TABLES Air Flow Flex Metal RD CFM Duct Round 80 6 5 Size SQ. IN. 120 7 6 or 3.5 x 10 5 20 160 8 7 6 28 175 8 8 or 3.5 x 14 7 38 200 9 8 or 6 x 8 8 50 300 10 9 or 8 x 8 9 64 1 400 11 10 or 10 x 8 (14 x 8 Panned Joist) 10 79 500 12 11 or 14 x 8 10 x 10 12 113 1.5 600 13 12 or 16 x 8 12 x 10 14 154 700 14 13 or 16 x 8 14 x 10 12 x 12 16 201 2 800 15 13 or 18 x 8 16 x 10 12 x 12 18 254 2.5 1000 16 14 or 22 x 8 18 x 10 14 x 12 20 314 3 1200 17 15 or 26 x 8 20 x 10 16 x 12 22 380 3.5 1400 18 16 or 30 x 8 22 x 10 18 x 12 24 452 4 1600 20 17 or 32 x 8 24 x 10 20 x 12 26 531 1800 20 18 or 28 x 10 22 x 12 28 616 5 2000 21 18 or 30 x 10 24 x 12 30 707 300 CFM per sq ft Gross Grill area 200 CFM per sq ft Gross Grill area Ton CFM Gross Sq Ft Gross Sq inches Ton CFM Gross Sq Ft Gross Sq inches 1.5 600 2.0 288 1.5 600 3 432 2 800 2.7 384 2 800 4 576 2.5 1000 3.3 480 2.5 1000 5 720 3 1200 4.0 576 3 1200 6 864 3.5 1400 4.7 672 3.5 1400 7 1008 4 1600 5.3 768 4 1600 8 1152 (Doug Garrett Building Performance & Comfort) Common Grille Sizes (GROSS SQUARE INCHES) 16 x 20 16 x 25 20 x 20 20 x 24 20 x 25 20 x 30 24 x 24 24 x 30 30 x 14 320 400 400 480 500 600 576 720 420 (DELTA-T INC, Gas Furn & AC CHARTS) AIR CONDITIONER (6 SQ. IN. PER 1,000 BTU's) GAS FURNACE (2 SQ. IN. PER 1,000 BTU's) 48,000 288 140,000 280 36,000 216 42,000 252 18,000 108 24,000 144 30,000 180 Supply and Return SQ IN Ducts Needed INPUT BTUS INPUT BTUS SQ IN Ducts Needed Supply and Return 100,000 120,000 80 120 160 200 240 40,000 60,000 80,000 NON - FILTER GRILLE FILTER GRILLE Round Duct Square Inch Equialency (Stud Cavity) Metal Duct Sizes Equivalent Rectangular *Duct Size Calculated at 0.1 inches of available static pressure for each 100 Equivalent Feet of Duct System. 242546819.xls.ms_office 8/29/2014
