State Water Heaters SUF60 Service Handbook page 7

GAS SUPPLY SYSTEMS
Low pressure building gas supply systems are defined as those systems that cannot under any circumstances
exceed 14" W.C. (1/2 PSI Gauge). These systems do not require pressure regulation. Measurements should
be taken to insure that gas pressures are stable and fall within the requirements stated on the water heater
rating plate. Readings should be taken with all gas burning equipment off (static pressure) and with all gas
burning equipment running at maximum rate (dynamic pressure). The gas supply pressure must be stable
within 1.5" W.C. (0.05 PSI Gauge) from static to dynamic pressure to provide good performance. Pressure
drops that exceed 1.5" W.C. (0.05 PSI Gauge) may cause rough starting, noisy combustion or nuisance
outages. Increases or spikes in static pressure during off cycles may cause failure to ignite or in severe
cases damage to appliance gas valves. If your low pressure system does NOT meet these requirements, the
installer is responsible for the corrections.
High Pressure building supply systems use pressures that exceed 14" W.C. (1/2 PSI Gauge). These
systems must use field supplied regulators to lower the gas pressure to less than 14" W.C. (1/2 PSI Gauge).
Appliances require gas regulators that are properly sized for the water heater input and deliver the rating plate
specified pressures. Gas supply systems where pressure exceeds 5 PSI often require multiple regulators to
achieve desired pressures. Systems in excess of 5 PSI building pressure should be designed by gas delivery
professionals for best performance. Water heaters connected to gas supply systems that exceed 14" W.C.
(1/2 PSI Gauge) at any time must be equipped with a gas supply regulator.
The minimum supply pressure is measured while gas is flowing (dynamic pressure). The supply pressure
should be measured with all gas fired appliances connected to the common main firing at full capacity. If
the supply pressure drops more than 1.5" W.C. (0.05 PSI Gauge) as gas begins to flow to the water heater
then the supply gas system including the gas line and/or the gas regulator may be restricted or undersized.
See Supply Gas Regulator section of this manual. The gas valve on all models has a maximum gas supply
pressure limit of 14" W.C. (1/2 PSI Gauge). The maximum supply pressure is measured while gas is not
flowing (static pressure).
SUPPLY GAS REGULATOR
Install a positive lock-up gas pressure regulator in the gas supply line if inlet gas pressure exceeds the
maximum supply gas pressure at any time. See "Gas Pressure Specifications" table on Page 4. Regulators
must be sized/used according to manufacturer's specifications.
If a positive lock-up regulator is required follow these instructions:
1. Positive lock-up gas pressure regulators must be rated at or above the input Btu/hr rating of the water
heater they supply.
2. Positive lock-up gas pressure regulator(s) should be installed no closer than 3 equivalent feet (1
meter) and no farther than 8 equivalent feet (2.4 meters) from the water heater's inlet gas connection.
3. After installing the positive lock-up gas pressure regulator(s) an initial nominal supply pressure setting
of 7.0" w.c. (1.74 kPa) for Natural Gas and 11.0" w.c. (2.74 kPa) for Propane (LP) while the water
heater is operating is recommended and will generally provide good water heater operation. Some
additional adjustment maybe required later to maintain a steady gas supply pressure.
4. When installing multiple water heaters in the same gas supply system it is required that individual
positive lock-up gas pressure regulators be installed at each unit.
Servicing should only be performed by a Qualified Service Technician 5