13
Figure 7. The water heater should 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 should directly communicate with the
outdoors or should communicate through a vertical or horizontal duct
to the outdoors or spaces that freely communicate with the outdoors
and should have a minimum free area of the following:
1. 1 square inch per 3000 Btu/hr (700 mm2 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.
Connedspaceshould 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 should communicate directly with outdoors. See Figure 8.
Each duct opening should have a minimum free area of 1 square inch
per 2,000 Btu/hr (1100 mm2 per kW) of the aggregate input rating of all
appliances installed in the enclosure.
When ducts are used, they should 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 should 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connedspacesonly.
Do not refer to these illustrations for the purpose of vent installation.
See Installation of Vent System on pages 19-20 for complete venting
installation instructions.
fIGure 9.
Theconnedspaceshouldbeprovidedwithtwopermanentvertical
ducts, one commencing within 12 inches (300 mm) of the top a nd
one commencing within 12 inches (300 mm) of the bottom of t he
enclosure. The vertical ducts should c ommunicate directly with the
outdoors. See Figure 9.
Each duct opening should have a minimum free area of 1 sq uare inch
per 4,000 Btu/hr (550 mm2 per kW) of the ag gregate input rating of
all appliances installed in the enclosure.
When ducts are used, they should be of the same cros s sectional
area as the free area of the openings to which they co nnect. The
minimum dimension of rectangular air ducts sh ould be not less than
3 inches.
aIr froM other Indoor spaces

fIGure 9a.

The confined space should be provided w ith two permanent
openings, one commencing within 12 inches (30 0 mm) of the top
and one commencing within 12 inches (300 mm) of the botto m of
the enclosure. See Figure 9A.
Each opening should communicate direct ly with an additional room(s)
ofsufcientvolumesothatthecombinedvolumeofallspacesmeets
thecriteriaforanUnconnedSpace.
Each opening should have a minimum free area of 1 square inc h per
1,000 Btu/hr (1100 mm2 per kW) of the aggregate input rating of all
appliances installed in the enclosure. Eac h opening should not be
less than 100 square inches (645 cm2).