Installation & Operation Manual
1
Determine unit location
(continued)
11
2. If combustion and ventilation air is taken from the
outdoors using a duct to deliver the air to the
equipment room, each of the two openings should be
sized based on a minimum free area of one square inch
per 2000 Btu/hr (11 cm
2
per kW) of input (see FIG. 1-3).
IMG00623
Figure 1-5_Combustion Air from Outside - Single
Opening
3. If air is taken from another interior space, each of the
two
openings specified above should have a net free
area of one square inch for each 1000 Btu/hr (22 cm
2
per kW) of input, but not less than 100 square inches
(645
cm
2
) (see FIG. 1-4).
4. If a single combustion air opening is provided to bring
combustion air in directly from the outdoors, the opening
must be sized based on a minimum free area of one square
inch per 3000 Btu/hr (7 cm
2
per kW). This opening must
be located within 12" (30 cm) of the top of the enclosure
(see FIG. 1-5).
IMG00622
Figure 1-4_Combustion Air from Interior Space
TABLE - 1B
MINIMUM RECOMMENDED COMBUSTION
AIR SUPPLY TO EQUIPMENT ROOM
Model
Number
*Outside Air from
2 Openings Directly from
Outdoors
*Outside Air from
1 Opening Directly
from Outdoors, in
2
Inside Air from
2 Ducts Delivered from
Outdoors
Inside Air from
2 Ducts Delivered from Interior
Space
Top
Opening, in
2
Bottom
Opening, in
2
Top
Opening, in
2
Bottom
Opening, in
2
Top
Opening, in
2
Bottom
Opening, in
2
500
125
(807 cm
2
)
125
(807 cm
2
)
167
(1077 cm
2
)
250
(1613 cm
2
)
250
(1613 cm
2
)
500
(3226 cm
2
)
500
(3226 cm
2
)
750
188
(1213 cm
2
)
188
(1213 cm
2
)
250
(1613 cm
2
)
375
(2420 cm
2
)
375
(2420 cm
2
)
750
(4839 cm
2
)
750
(4839 cm
2
)
1000
250
(1613 cm
2
)
250
(1613 cm
2
)
333
(2149 cm
2
)
500
(3226 cm
2
)
500
(3226 cm
2
)
1000
(6452 cm
2
)
1000
(6452 cm
2
)
1500
375
(2420 cm
2
)
375
(2420 cm
2
)
500
(3226 cm
2
)
750
(4839 cm
2
)
750
(4839 cm
2
)
1500
(9678 cm
2
)
1500
(9678 cm
2
)
2000
500
(3226 cm
2
)
500
(3226 cm
2
)
667
(4303 cm
2
)
1000
(6452 cm
2
)
1000
(6452 cm
2
)
2000
(12904 cm
2
)
2000
(12904 cm
2
)
*Outside air openings shall directly communicate with the outdoors. When combustion air is drawn from the outside through a
duct, the net free area of each of the two openings must have twice (2 times) the free area required for Outside Air/2 Openings. The
above requirements are for the water heater only; additional gas fired appliances in the equipment room will require an increase in
the net free area to supply adequate combustion air for all appliances.
