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1
Determine water heater location
Figure 1-5 Combustion Air through Ducts
2. If combustion and ventilation air is taken from the
outdoors using a duct to deliver the air to the mechanical
room, each of the two openings should be sized based on
a minimum free area of one square inch per 2000 Btu/hr
(11cm
2
per kW).
Figure 1-6 Air from an Interior Space
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 (22cm
input, but not less than 100 square inches (645 cm
6
Figure 1-7 Air from Outside - Single Opening
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 (7cm
opening must be located within 12" (30 cm) of the top of
the enclosure.
5. See venting section for combustion air requirements on
E+Venting and direct vent applications.
MINIMUM RECOMMENDED COMBUSTION
AIR SUPPLY TO MECHANICAL ROOM
Input/
BTU
150,000
199,000
250,000
300,000
*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 opening must have
twice (2 times) the free area required for each Outside Air
Openings. The above requirements are for the appliance
2
per kW) of
only, additional gas fired appliances in the mechanical room
2
).
will require an increase in the net free area to supply
adequate combustion air for all appliances. Combustion air
requirements are based on the latest edition of the National
Fuel Gas Code, ANSI Z223.1, in Canada refer to CSA
International CAN/CGA B149.1 or B149.2 Installation Code.
Check all local code requirements for combustion air.
Installation & Service Manual
TABLE 1A
Outside Air*
Outside Air*
2 Openings
1 Opening
38 in
2
50 in
2
50 in
2
67 in
2
63 in
2
83 in
2
2
2
75 in
100 in
per kW). This
2
Inside Air*
2 Openings
150 in
2
200 in
2
250 in
2
2
300 in
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