400 kW standby / 360 kW prime · Natural Gas / LPG / Dual Fuel (NG/LPG) · Liquid-cooled
400 kW gaseous-fueled commercial standby generator. Kohler/Rehlko 400REZXB — the flagship of Kohler's industrial gaseous lineup for large facilities and paralleling arrays. Note: the 400 kW Kohler gas genset is sold as the 400REZXB, not as 'KG400'.
The 400 kW Kohler/Rehlko gaseous standby generator is sold as the 400REZXB — there is no Kohler model called "KG400." We've kept this URL because customers commonly search "Kohler KG400" when comparing 400 kW gas gensets, and we want them landing on accurate information.
The 400REZXB is the upper end of Kohler's industrial gaseous lineup: a Doosan/PSI 21.9L V12, turbocharged and aftercooled, producing 605 HP at 1800 RPM on natural gas or propane without a drop of diesel.
Above 400 kW gaseous, the answer is paralleling. Two 400REZXB units provide 800 kW with full N+1 redundancy; three provide 1.2 MW. This makes the 400REZXB a building block for large gaseous paralleling arrays at campuses, hospitals, and government facilities where air quality districts restrict diesel emissions.
The 400REZXB is our largest gaseous service platform. Every unit we maintain is on a walk-in or container enclosure — there's no practical way to service a 21.9L V12 in a standard weather-protective cabinet. The aftercooler adds a service item (condensation drain, core inspection) that doesn't exist on the smaller naturally-aspirated or basic turbo units.
Engineering specifications
Physical
Length
288 in
Width
103 in
Height
120 in
Wet weight
16,000 lb
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Estimate runtime for the Kohler 400REZXB (400 kW Gas)
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
4,200,000 BTU/hr≈ 4200.0 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 Kohler 400REZXB (400 kW Gas) under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.
Oil & filter
Every 500 hours or 12 months
Coolant change
Every 4000 hours
Air filter
Every 1000 hours
Spark plugs
Every 2000 hours
Major overhaul
≈ 24,000 hours
Load bank test
Every 12 months
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.
No. The KG industrial gaseous lineup tops out at the KG200. The 400 kW Kohler/Rehlko gaseous standby unit is sold as the 400REZXB. Its spec sheet is published as G4-192.
What is the standby rating of the Kohler 400 kW gas generator?
The 400REZXB is rated 400 kW standby (360 kW prime) at 60 Hz, powered by a Doosan/PSI D219TIC 21.9L turbocharged-aftercooled V12 at 1800 RPM (605 HP at the engine shaft).
Is the 400REZXB the largest gas generator Kohler/Rehlko makes?
Among the REZXB stationary spark-ignition lineup, the 400REZXB and 450REZXB share the same 21.9L V12 platform; 450REZXB is the higher-rated variant. For requirements above that, Kohler recommends paralleling multiple REZXB units.
What ATS for 400 kW?
At 480V three-phase: 600-800A ATS. ASCO 7000 Series with bypass-isolation is standard. For paralleled arrays, master ATS with load management is typical.
