Air Requirements; Air Supply - A.O. Smith SERIES 120 Service Handbook

Table 1
‡
Maximum Supply Gas Pressure
†
Minimum Supply Gas Pressure
*
Manifold Gas Pressure
‡ Maximum supply pressure; readings are taken while gas is not fl owing (static pressure) AND while gas is fl owing (dynamic pressure).
Supply pressure must never exceed this maximum value.
† Minimum supply gas pressure; readings are taken while gas is not fl owing (static pressure) AND while gas is fl owing (dynamic
pressure). Supply pressure must never fall below the minimum values. Supply gas pressures should be measured with all gas fi red
appliances conencted to a common main fi ring at full capacity. If supply pressure drops more than 1.5" W.C. as gas begins to fl ow,
the supply gas system (gas line/regulator) may be restricted or undersized. See the instruction manual for more information.
* Manifold gas pressure; reading can only be taken while gas is fl owing. Reading taken should be ± 0.3" W.C. of the listed value.
These water heaters are certifi ed for use without modifi cation for altitudes up to 10,000 feet. For elevations above 10,000 feet
(3,048 meters), see High Altitude Installations section of instruction manual.

AIR REQUIREMENTS

Carefully review the requirements for combustion and ventilation air in the instruction
manual that came with the water heater. Failure to meet these requirements when the
water heater is installed or overlooking their importance when servicing the water heater
often results in operational problems (some are listed below), needless down time,
unnecessary parts replacement, and customer dissatisfaction.
Ensure additional air for combustion and ventilation is provided when additional gas fired
appliances are installed to increase hot water supply in an existing location.

Air Supply

Stoichiometric or theoretical complete combustion requires 10 cubic feet of air per 1,000
BTUH of gas supplied. The National Fuel Gas Code also recommends an additional 2.5
cubic feet of "excess" air. For information on minimum make-up air opening sizes for
various building installations, refer to the National Fuel Gas Code NFPA 54, ANSI Z223.1.
Servicing should only be performed by a Qualifi ed Service Agent
INSTALLATION CONSIDERATIONS
NATURAL GAS
10" W.C. (2.49 kPa)
5.2" W.C. (1.29 kPa)
3.5" W.C. (0.87 kPa)
Figure 1
6
PROPANE (LP) GAS
12" W.C. (2.99 kPa)
11" W.C. (2.74 kPa)
10" W.C. (2.49 kPa)