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440 01 2021 01
3. One opening
MUST
be within 12
²
of the floor and the sec-
ond opening within 12
²
of the ceiling.
a.
1 sq. in of free area per 3,000 BTUH (700 mm
2
/kW) for
combined input of all gas appliances in the space (see
Table 1
) and
b.
not less than the sum of the areas of all vent connectors in
the space.
The opening shall commence within 12
²
of the top of the enclo-
sure. Appliances shall have clearances of at least 1
²
from the sides
and back and 6
²
from the front. The opening shall directly commu-
nicate with the outdoors or shall communicate through a vertical or
horizontal duct to the outdoors or spaces (crawl or attic) that freely
communicate with the outdoors.
4. Size openings and ducts per
Table 1.
a. Indoor openings that comply with the
Indoor Combus-
tion Air
Method below and
b. Outdoor openings located as required in the
Outdoor
Combustion Air
Method above and
c.
Outdoor openings sized as follows.
1) Calculate the
Ratio
of all Indoor Space volume
divided by required volume for
Indoor Combustion
Air
Method.
2) Outdoor opening size reduction
Factor
is
1
minus
the
Ratio
in 1) above.
3) Minimum size of Outdoor openings shall be the size
required in
Outdoor Combustion Air
Method
above multiplied by reduction
Factor
.
5. Horizontal duct openings require 1 square inch of free area
per 2,000 BTUH of combined input for all gas appliances in
area
(
see
Table 1)
.
6. Vertical duct openings or openings directly to outside re-
quire 1 square inch of free area per 4,000 BTUH for com-
bined input of all gas appliances in area
(
see
Table 1).
Table 1
Free Area
BTUH
Minimum Free Area Required for Each Opening or Duct to Outdoors
BTUH
Input
Rating
Two Horizontal Ducts
(sq. in./2,000 BTUH)
Single Opening
(sq. in./3,000 BTUH)
Two Vertical Ducts or
Openings
(sq. in./4,000 BTUH)
Rd Duct
(sq. in. /4,000 BTUH)
50,000
25 sq. in.
16.7 sq. in.
12.5 sq. in.
4
²
75,000
37.5 sq. in.
25 sq. in.
18.75 sq. in.
5
²
100,000
50 sq. in.
33.3 sq. in.
25 sq. in.
6
²
125,000
62.50 sq. in.
41.7 sq. in.
31.25 sq. in.
7
²
EXAMPLE:
Determining Free Area
Furnace
100,000
Furnace
100,000
+
+
Water Heater
30,000
Water Heater
30,000
=
=
Total Input
(130,000
¸
4,000)
Total Input
(130,000
¸
2,000)
=
=
32.5 Sq. In. Vertical
65 Sq. In. Horizontal
Unconfined Space Installation
CARBON MONOXIDE POISONING HAZARD
Failure to supply additional air by means of
ventilation grilles or ducts could result in death or
personal injury.
An unconfined space or homes with tight
construction may not have adequate air infiltration
for proper combustion and ventilation of flue gases.
Most homes will require additional air.
!
WARNING
An unconfined space is defined as an area having a minimum vol-
ume of 50 cubic feet per 1,000 Btuh total input rating for all gas ap-
pliances in area. Refer to
Table 2
for minimum area required.
T bl 2
MINIMUM SPACE VOLUME FOR 100% COMBUSTION AND VENTILATION AIR FROM INDOORS (ft
3
)
Table 2
Other Than Fan- Assisted Total
(1,000’s Btuh)
Fan- assisted Total
(1,000’s Btuh)
ACH
30
40
50
50
75
100
125
0.60
1,050
1,400
1,750
1,250
1,875
2,500
3,125
0.50
1,260
1,680
2,100
1,500
2,250
3,000
3,750
0.40
1,575
2,100
2,625
1,875
2,813
3,750
4,688
0.30
2,100
2,800
3,500
2,500
3,750
5,000
6,250
0.20
3,150
4,200
5,250
3,750
5,625
7,500
9,375
0.10
6,300
8,400
10,500
7,500
11,250
15,000
18,750
0.00
NP
NP
NP
NP
NP
NP
NP
NP = Not Permitted
Table 2
Minimum Space Volumes were determined by using the
following equations from the National Fuel Gas Code ANSI
Z223.1/NFPA 54--2002, 8.3.3.2:
1.
For
other than fan--assisted appliances
such as a draft
hood--equipped water heater,
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