Table 3 - Minimum Free Area Required for Each Combustion Air Opening or Duct to Outdoors
TWO HORIZONTAL DUCTS SINGLE DUCT OR OPENING TWO OPENINGS OR
(1 SQ. IN./2,000 BTUH) (1 SQ. IN./3,000 BTUH) VERTICAL DUCTS
FURNACE (1,100 SQ. MM/KW) (734 SQ. MM/KW) (1 SQ. IN./4,000 BTUH)
INPUT (550 SQ. MM/KW)
(BTUH) Free Area of Round Duct Free Area of Round Duct Free Area of Open- Round Duct
Opening and Duct Opening and Duct ing and Duct
Sq, In (Sq, mm) In. (mm) Dia Sq, In (Sq, mm) In. (mm) Dia Sq, In (mm) In. (mm) Dia.
40,000* 20 (12904) 5 (127) 14 (8696) 5 (127) 10 (6452) 4 (102)
60,000 30 (19355) 6 (152) 20 (13043) 5 (127) 15 (9678) 5 (127)
80,000 40 (25807) 7 (178) 27 (17391) 6 (152) 20 (12904) 5 (127)
100,000 50 (32258) 8 (203) 34 (21739) 7 (178) 25 (16130) 6 (152)
120,000 60 (38709) 9 (229) 40 (26087) 7 (178) 30 (19355) 6 (152)
140,000" 70 (45161) 10 (254) 47 (30435) 8 (203) 35 (22581) 7 (178)
*Not all families have these models.
EXAMPLES: Determining Free Area
FURNACE WATER HEATER TOTAL INPUT
100,000 + 30,000 = (130,000 divided by 4,000) = 32.5 Sq. In. for each two Vertical Ducts or Openings
60,000 + 40,000 = (100,000 divided by 3,000) = 33.3 Sq. In. for each Single Duct or Opening
80,000 + 30,000 = (110,000 divided by 2,000) = 55.0 Sq, In. for each two Horizontal Ducts
Table 4 - Minimum Space Volumes for 100 % Combustion, Ventilation and Dilution Air from Outdoors
OTHER THAN FAN-ASSISTED TOTAL FAN-ASSISTED TOTAL
(1,000'S BTUH GAS INPUT RATE) (1,000'S BTUH GAS INPUT RATE)
30 40 50 40 60 80 100 120 140
ACH Space Volume Ft3 (M3)
1,050 1,400 1,750 1,400 1,500 2,000 2,500 3,000 3,500
0,60 (29.7) (39.6) (49.5) (39.6) (42.5) (56.6) (70.8) (84.9) (99.1)
1,260 1,680 2,100 1,680 1,800 2,400 3,000 3,600 4,200
0,50 (35.6) (47.5) (59.4) (47.5) (51.0) (67.9) (84.9) (101.9) (118.9)
1,575 2,100 2,625 2,100 2,250 3,000 3,750 4,500 5,250
0,40 (44.5) (59.4) (74.3) (59.4) (63.7) (84.9) (106.1 ) (127.3) (148.6)
2,100 2,800 3,500 2,800 3,000 4,000 5,000 6,000 7,000
0,30 (59.4) (79.2) (99.1) (79.2) (84.9) (113.2) (141.5) (169.8) (198.1 )
3,150 4,200 5,250 4,200 4,500 6,000 7,500 9,000 10,500
0.20 (89.1) (118.9) (148.6) (118.9) (127.3) (169.8) (212.2) (254.6) (297.1)
6,300 8,400 10,500 8,400 9,000 12,000 15,000 18,000 21,000
0.10 (178.0) (237.8) (297.3) (237.8) (254.6) (339.5) (424.4) (509.2) (594.1)
0,00 NP NP NP NP NP NP NP NP NP
NP = Not Permitted
-- 1 SQIN.
PER 4000
Duss-h / °TU.
OUTDOORSI "._,_._
_ I I ! JJ }i
(305mm) 12"MAX] ]1 I D II 1-_
1sa,a &/ I _o IVENT k-l_
PER2000 "/ ;IBI _ _ I THROUGH FI:_
BTUFF !i I <;5 I ROOF F_ql S._
,' //I II I1£'"
, _:
DUOTS// II 8
.uT;°ORS// II
o
// II,so
..........NN N ',
/ / I II 40(
! J I i i BTL
1SQN /J I _ _ = _M ,
i .......... _ L L_P=-I
PER 2000 ,_ /'IAI _ _ 7- _:_--
BTUFF T :0
12
A l i i 12"MAX/
r(305mm)"
OROULAT,.GA,RDUCTS J\
:_8TX_ 1so,..
I TO PER 4000
OUTDOORS BTUH*
(305mm)
(305mm)
*Minimum dimensions of 3-in. (76 mm).
NOTE: Use any of the following combinations of openings:
A&BC&DD&EF&G
A03174
Fig. 6 - Air for Combustion, Ventilation, and Dilution for
Outdoors
CIRCULATING AiR
DUCTS
I I
1 1
I I
INTERIOR
HEATED
SPACE
I I
I I
VENT THROUGH ROOF
_: 12" AX(S05mm)
o
-_- 1 SQ IN.
PER 1000
BTUH* IN DOOR
OR WALL
UNCONFINED
SPACE
6" MIN (152mm)
(FRONT)0
1 SQ IN.
PER 1000
BTUH* IN DOOR
-- OR WALL
12" MAX (305mm)
l'
CIRCULATING AIR DUCTS
* Minimum opening size is 100 sq. in. (64516 sq. mm) with minimum dimensions
of 3 in. (76 mm)
1-Minimum of 3 in. (76 mm) when type-B1 vent is used.
A03175
Fig. 7 - Air for Combustion, Ventilation, and Dilution from
Indoors
11
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