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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 (ft s)
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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