The Hipower HNI-350 is a 350 kW standby natural gas generator powered by a PSI spark-ignited engine. Part of Hipower's CARB-certified HNI series, the HNI-350 fills the gap between the 300 kW and 450 kW models — covering large commercial buildings, data centers, and industrial facilities where natural gas is the preferred or only practical fuel for standby.
At 350 kW, gas supply infrastructure becomes a critical project consideration. A properly sized gas service — meter capacity, service pressure, pipe diameter — must be confirmed before the installation is finalized. Projects that clear the gas supply hurdle gain the operational advantages of utility-supplied fuel: no diesel storage, no SPCC plan, no fuel delivery logistics.
The HNI-350 uses a PSI turbocharged spark-ignited engine at 1800 RPM. PSI is a leading OEM in the North American stationary gas engine market, supplying multiple generator manufacturers with field-proven platforms. The specific engine model designation for the 350 kW class requires verification against OEM documentation.
Maintenance follows the HNI series pattern: spark plugs and oil changes at 1000-hour intervals, annual gas system inspection, no DPF or DEF servicing.
The HNI-350 is CARB certified as part of the full HNI series (30–1000 kW). California permit-by-rule applies, removing the source test and air district variance process that non-certified engines require. In the 300–450 kW power class, CARB-certified natural gas options outside the Big 4 are limited — the HNI-350 is one of the few.
OnPoint Generators services large natural gas standby generators throughout Northern California. Hospitals, data centers, and large commercial buildings in our service area that operate on natural gas find that gas standby integrates naturally with their existing fuel infrastructure — eliminating the separate diesel storage, inspection, and delivery program that diesel standby requires.
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Adjust load percent and tank size to estimate runtime. Pre-filled with this model's spec where available.
Estimate runtime on this tank
Fuel demand at 75% load
3,675,000 BTU/hr≈ 3675.0 cf/min @ 1,000 BTU/cf
On utility natural gas the runtime is generally unlimited provided the supply line and meter can deliver this BTU/hr at the engine's required inlet pressure (typically 5–14" WC residential, up to 5 psi commercial). Confirm against the OEM's published fuel-pressure spec.
Service intervals
Manufacturer-recommended intervals for the Hipower HNI-350 under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.
Oil & filter
Every 1000 hours or 12 months
Air filter
Every 500 hours
Spark plugs
Every 1000 hours
Major overhaul
≈ 30,000 hours
Common failure modes
What we've seen fail on this platform. Use as a service-planning reference, not a diagnostic — actual failure modes depend heavily on duty cycle and maintenance history.
Component
Symptom
Typical hours
Severity
Spark plugs
Erosion from natural gas combustion — replace on schedule to prevent misfire under load
1,000+
minor
Gas pressure regulator
Pressure drop under full load — verify regulator capacity matches demand
The HNI-350 uses a PSI spark-ignited engine. The specific engine model for this output class has not been confirmed from OEM documentation. <!-- NEEDS VERIFICATION: confirm PSI engine model for HNI-350 -->
Is the HNI-350 CARB certified?
Yes. The full HNI series (30–1000 kW) holds CARB certification. The HNI-350 qualifies for California permit-by-rule without an air district variance.
What applications is the HNI-350 suited for?
Large commercial buildings, data centers, hospitals, and industrial facilities where 350 kW of natural gas standby replaces the need for diesel storage and management. California facilities with sufficient gas service find this unit a compelling alternative to diesel in the same class.
What gas supply infrastructure is needed for 350 kW?
A 350 kW natural gas generator requires a high-capacity gas service. Supply line sizing, meter capacity, and regulator performance must be engineered for the full-load BTU demand. Engage a licensed mechanical engineer for gas system design.
Can the HNI-350 run on LP?
Yes. Available in natural gas, LP, and dual-fuel configurations.
Who services HNI units in the 350 kW class in Northern California?
OnPoint Generators services Hipower HNI units throughout Northern California, including units in the 300–450 kW range.
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