14
Figure 7. The water heater shall have clearances of at least 1 inch
(25 mm) from the sides and back and 6 inches (150 mm) from the
front of the appliance. The opening shall directly communicate with
the outdoors or shall communicate through a vertical or horizontal duct
to the outdoors or spaces that freely communicate with the outdoors
and shall have a minimum free area of the following:
1. 1 square inch per 3000 Btu/hr (700 mm
2
per kW) of the total input
rating of all appliances located in the enclosure, and
2. Not less than the sum of the areas of all vent connectors in space.
outdoor aIr throuGh two horIZontal ducts
fIGure 8.
Confined space shall be provided with two permanent horizontal
ducts, one commencing within 12 inches (300 mm) of top and one
commencing within 12 inches (300 mm) of bottom of enclosure. Horizontal
ducts shall communicate directly with outdoors. See Figure 8.
Each duct opening shall have a minimum free area of 1 square inch
per 2,000 Btu/hr (1100 mm
2
per kW) of the aggregate input rating of all
appliances installed in the enclosure.
When ducts are used, they shall be of the same cross sectional area
as the free area of the openings to which they connect. The minimum
dimension of rectangular air ducts shall be not less than 3 inches.
outdoor aIr throuGh two vertIcal ducts
The illustrations shown in this section of the manual are a reference for
the openings that provide fresh air into confined spaces only.
Do not refer to these illustrations for the purpose of vent installation.
See Installation of Vent System on pages 19-26 for complete venting
installation instructions.
fIGure 9.
The confined space shall be provided with two permanent vertical
ducts, one commencing within 12 inches (300 mm) of the top and
one commencing within 12 inches (300 mm) of the bottom of the
enclosure. The vertical ducts shall communicate directly with the
outdoors. See Figure 9.
Each duct opening shall have a minimum free area of 1 square inch
per 4,000 Btu/hr (550 mm
2
per kW) of the aggregate input rating of
all appliances installed in the enclosure.
When ducts are used, they shall be of the same cross sectional
area as the free area of the openings to which they connect. The
minimum dimension of rectangular air ducts shall be not less than
3 inches.
aIr froM other Indoor spaces
fIGure 9a.
The confined space shall be provided with two permanent openings,
one commencing within 12 inches (300 mm) of the top and one
commencing within 12 inches (300 mm) of the bottom of the
enclosure. See Figure 9A.
Each opening shall communicate directly with an additional room(s)
of sufficient volume so that the combined volume of all spaces meets
the criteria for an Unconfined Space.
Each opening shall have a minimum free area of 1 square inch per
1,000 Btu/hr (1100 mm
2
per kW) of the aggregate input rating of all
appliances installed in the enclosure. Each opening shall not be less
than 100 square inches (645 cm
2
).
