Wet Stacking
What it means.
Wet stacking is the buildup of unburned fuel and carbon in a diesel generator’s exhaust system, caused by running the engine below roughly 30% of its rated load for extended periods. The engine never reaches the combustion temperature needed to burn fuel completely. Left alone it fouls injectors, contaminates oil, restricts the exhaust, and damages pistons and rings, which is why NFPA 110 sets the monthly exercise load at 30% of nameplate.
Governing standard
The 30% minimum load in NFPA 110 Section 8.4.2 exists largely to prevent wet stacking. Where a site cannot reach 30% with building load, the standard calls for a supplemental load bank test to burn the exhaust clean.
Related service
Hedgehog Power Systems handles this under Engine Maintenance & Rebuild.
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Power that stays on.
Preventive maintenance, testing, and repair for standby generators across Illinois and the Midwest. One call reaches a technician, not a call center.