(unconfined) spaces or smaller (confined) spaces,
such as closets or small rooms.
Requirements for Unconfined Spaces
An unconfined space is an area with at least 50 cubic
feet for each 1,000 BTUH (4.8 m
3
/kW) of the total
input rating for all gas appliances installed in that
space. Water heaters installed in unconfined spaces
do not usually require outdoor air to function properly.
However, in buildings with tight construction (heavy
insulation, vapour barriers, weather stripping, etc.) and
particularly in modern buildings, additional fresh air
may need to be provided. For instructions on obtaining
additional air supply, see the requirements below for
confined spaces.
Requirements for Confined Spaces
A confined space is an area where the volume is less
than 50 cubic feet for each 1,000 BTUH (4.8 m
3
/kW)
of
the total input rating for all gas appliances installed in
that space. Water heaters installed in confined spaces
require additional air. This can be provided in two
ways:
In Canada (refer to CAN/CSA B149.1)
1) All Air From Inside the Building (see Figure 2):
The confined space shall be provided with
one opening of one (1) square inch per 1,000 BTUH
(22.0 cm
2
/kW) communicating directly with one or
more rooms of sufficient volume, so that the com-
bined volume of all spaces meets the criteria for an
unconfined space for all the appliances installed in
that confined space.
2) All Air From Outdoors: (see Figure 3):
An air-supply shall be provided with one open-
ing that communicates directly with the outdoors
by means of a duct. This duct shall be sized
according to CAN/CSA B149.1 and terminate within
1 foot above and within 2 feet horizontally from
the burner level of the appliance having the
largest input.
In U.S.A. (refer to ANSI Z223.1/NFPA 54)
1) All Air From Inside the Building (see Figure 4):
The confined space shall be provided with two
permanent openings communicating directly with
one or more rooms of sufficient volume, so that
the combined volume of all spaces meets the
criteria for an unconfined space. The total input
rating of all gas appliances installed in the
combined space shall be considered in making this
determination.
Each opening shall have a minimum free area of
one (1) square inch per 1,000 BTUH (22.0 cm
2
/
kW) of the total input rating of all gas appliances in
the confined space, but not less than 100 square
inches (645.16 cm
2
). One opening shall commence
within 6 inches (15.2 cm) of the top and one within 6
inches (15.2 cm) of the bottom of the enclosure.
2) All Air From Outdoors:
The confined space shall be provided with two
permanent openings, one commencing within six
5
Figure 4
INSTALLATION INSTRUCTIONS
Confined Space
Inlet air duct
18''
24''
Confined Space
Permanent
Opening
--------------
1 square inches /
1000 BTUH
Figure 3Figure 2
Figure 3
Confined Space
Inlet air duct
18''
24''
Confined Space
Permanent
Opening
--------------
1 square inches /
1000 BTUH
Figure 2
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