Requirements for Unconfined Spaces
Water heaters installed in unconfined spaces do not
usually require outdoor air to function properly.
However, if the water heater is located in an uncon-
fined space in a building having insufficient
infiltration, air for combustion and additional ventilation
should be obtained from the outdoors or from spaces
freely communicating with the outdoors (
see Figure
2
). Under these conditions, a permanent opening to
the outdoors should be provided so that the total air
received through this opening will be at least as much
as would be admitted by openings having a total free-
flow area of one (1) square inch per 5,000 BTU/h (4.4
cm
2
/kWh) of the total input rating of all oil-fired appli-
ances.
Requirements for Confined Spaces (Indoor
Combustion and Ventilation Air)
A water heater that is located in a confined space and
obtains all of its air for combustion and ventilation from
within the conditioned space of the building should be
provided with two permanent openings, one near the
top of the enclosure and another one near the bottom
(
see Figure 3
). Each opening should have a free-flow
area of not less than one (1) square inch per 1,000
BTU/h (22 cm
2
/kWh) of the total input rating of all
oil-fired appliances in the enclosure, freely communi-
cating with interior areas that have in turn adequate
infiltration from the outdoors.
Requirements for Confined Spaces (Outdoor
Combustion and Indoor Ventilation Air)
A water heater that is located in a confined space and
that obtains its combustion air from outdoors and
ventilation air from within the conditioned space of
the building should be provided with two permanent
openings, one near the top of the enclosure and
another one near the bottom (
see Figures 4 and 5
).
Each opening should have a free-flow area of not less
than one (1) square inch per 1,000 BTU/h (22
cm
2
/kWh) of the total input rating of all oil-fired appli-
ances in the enclosure, freely communicating with
interior areas that have in turn adequate infiltration
from the outdoors. A combustion air supply opening
to the outdoors should be provided so that the total air
received through the opening will be at least as much
as would be admitted by openings having a total free-
flow area of one (1) square inch per 5,000 BTU/h (4.4
cm
2
/kWh) of the total input rating of all oil-fired appli-
ances in the enclosure.
Requirements for Confined Spaces (Outdoor
Combustion and Ventilation Air)
A water heater that is located in a confined space and
that obtains all of its air for combustion and ventilation
from outside the building shall be provided with two
permanent openings, one near the top of the
4
INSTALLATION INSTRUCTIONS
Figure 2
Figure 3
2'' Min.
2'' Min.
2'' Min.
18'' Min.
24'' Min.
2'' Min.
Figure 1
