Payne PG8J - Page 9

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TABLE 2—MINIMUM FREE AREA REQUIRED FOR EACH COMBUSTION AIR OPENING OR DUCT TO OUTDOORS
FURNACE
INPUT
(BTUH)
TWO HORIZONTAL DUCTS
(1 SQ. IN./2,000 BTUH) (1,100 SQ. MM/KW)
SINGLE DUCT OR OPENING
(1 SQ. IN./3,000 BTUH) (734 SQ. MM/KW)
TWO OPENINGS OR VERTICAL DUCTS
(1 SQ. IN./4,000 BTUH) (550 SQ. MM/KW)
Free Area of Open-
ing and Du ct
(Sq. In.)
Round Duct
(In. Dia)
Free Area of
Opening and Duct
(Sq. In.)
Round Duct
(In. Dia)
Free Area of Open-
ing and Du ct
(Sq. In.)
Round Duct
(In. Dia)
44,000 22 6 14.7 5 11 4
66,000 33 7 22 6 16.5 5
88,000 44 8 29.3 7 22 6
110,000 55 9 36.7 7 27.5 6
132,000 66 10 44 8 33 7
154,000 77 10 51.3 9 38.5 8
EXAMPLES: Determining Free Area
FURNACE WATER HEATER TOTAL INPUT
110,000 + 30,000 = (140,000 divided by 4,000) = 35.0 Sq. In. for each two Vertical Ducts or Openings
66,000 + 40,000 = (106,000 divided by 3,000) = 35.3 Sq. In. for a Single Duct or Opening
88,000
+ 30,000 = (118,000 divided by 2,000) = 59.0 Sq. In. for each of two Horizontal Ducts
TABLE 3—MINIMUM SPACE VOLUMES FOR 100% COMBUSTION, VENTILATION, AND DILUTION FROM INDOORS
ACH
OTHER THAN FAN---ASSISTED TO-
TAL
(1,000’S BTUH GAS INPUT RATE)
FAN---ASSISTED TOTAL
(1000’S BTUH GAS INPUT RATE)
30 40 50 44 66 88 110 132 154
SpaceVolume(ft.
3
)
0.60 1,050 1,400 1,750 1,100 1,650 2,200 2,750 3,300 3,850
0.50 1,260 1,680 2,100 1,320 1,980 2,640 3,300 3,960 4,620
0.40 1,575 2,100 2,625 1,650 2,475 3,300 4,125 4,950 5,775
0.30 2,100 2,800 3,500 2,200 3,300 4,400 5,500 6,600 7,700
0.20 3,150 4,200 5,250 3,300 4,950 6,600 8,250 9,900 11,550
0.10 6,300 8,400 10,500 6,600 9,900 13,200 16,500 19,800 23,100
0.00 NP NP NP NP NP NP NP NP NP
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