Table 1--Minimum Free Area Required for Each Combustion Air Opening or Duct to Outdoors
TWO HORIZONTAL DUCTS SINGLE DUCT OR OPENING TWO OP_=N_NGS OR VI=RTICAL DUCTS
FURNACE
iNPUT
(BTUH)
44,000
66,000
88,000
110,000
132,000
154,000
{1 SQ. IN.I2,000 BTUH)
Free Area of
Opening and Duct
(sq. in.)
22
33
44
55
66
77
{t,100 SO. MMtKW)
Round Duct
(in. Dia)
6
7
8
9
10
10
(1 SQ. IN.t3,000 BTUH)
Free Area of
Opening and Duct
(sq In.)
14.7
22
29.3
36.7
44
51.3
(734 SO. MM/KW)
Round Duct
(in. Dia)
5
6
7
7
8
9
{1 SQ. IN.14,000 BTUH)
Free Area of
Opening and Duct
(Sq In.)
11
16.5
22
27.5
33
38.5
(550 SO. MMiKW)
Round Duct
(In. Dia)
4
5
6
6
7
8
EXANPLES: Determining Free Area
FURNACE WATER HEATER TOTAL INPUT
t10,000 + 30,000 = (140,000 divided by 4,000) 35.0 Sq. In. for each two Vertical Ducts or Openings
66,000 + 40,000 = (t06,000 divided by 3,000) 35.3 Sq. In. for a Single Duct or Opening
88,000 + 30,000 = (t 18,000 divided by 2,000) 59.0 Sq. tn. for each of two Horizontal Ducts
Table 2--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)
ACH 30 I 40 I 50 44 166 I 88 1110 1132 1154
Space Volume (fts)
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.t0 6,390 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
CARBON MONOXIDE POISONING HAZARD
Failure to supply outdoor air via grilles or dncts could result
in death and/or personal i11iury.
Many homes require air to be supplied flora outdoors for
ftlrnace combustion, ventilation, and dilution of flue gases.
The _b.mace combustion air supply must be provided in
accordance with this instruction manual.
The Standard Method:
1. The space has no less volume than 50 cubic f)et per 1,go0
Btuh of the n_axinmm input ratings for all gas appliances
installed in the space and
2. The air infiltration rate is not known to be less than 0.40 air
changes per hour (A(H)
The Known Air Infiltration Rate Method shall be used, if the
infiltration rate is known to be:
1. Less than 0.40 ACH and
2. Equal to or greater than 0.10 ACH
Infiltration rates greater than 0.60 ACH shall not be used. The
minimum required volume of tl_e space varies with the number of
ACH and shall be determined per Table 2 or Equations 1 and 2.
Determine the mininmna required volume for each appliance in the
space and add the volumes together to get the total mininmm
required volume %r the space.
Table 2:Minimum Space Volumes were detem_ined by using the
following equations flora the Yationa/ F_el Gas Co&_ A:\%7
Z223.J-2002/YFP.t 54-2002,&3.2.2:
1. For ether than fan-assisted appliances, such as a draft
hoodoequipped water heater:
'Volume - 21ft3
ether ACH
A04002
2, For fan-assisted appliances such as this _hrnace:
- 15ft3f- If_,
Volume Fan AOH 00(_ B-_u/hr
A04003
Iom_ combined input of all other than fan-assisted appli-
ances in Bmihr
I_.,, combined input of all fan-assisted appliances in Bm&r
ACH air changes per hour (ACH shall not exceed 0.60.)
The following requirements apply to the Standard Method and to
the Known Air Infiltration Rate Method.
16
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