Cooling Method Matters
Air-Cooled or Liquid-Cooled: What Actually Matters
The single biggest technical decision after kW sizing is air-cooled vs liquid-cooled. Both cool the engine but differently, and the difference shows up in real ways during a multi-day outage.
Air-cooled units use fan-driven airflow across the engine block and cylinder heads. Simpler, lighter, less expensive, and perfectly adequate for the vast majority of residential installs. This is the entire Guardian series.
Liquid-cooled units circulate coolant through a radiator like a car engine. Run cooler under sustained load, handle longer outages and higher power draw better, and produce cleaner, more stable output. This is the entire Protector series.
Air-Cooled: Simpler, Volume Choice
Runs at 3,600 RPM. Air filter, spark plugs, and oil are the main service items. Adequate for outages up to a few days at typical residential load. Every Generac Guardian is air-cooled.
Liquid-Cooled: Sustained High Load
Larger engine, radiator, coolant system. Better temperature stability during multi-day outages under heavy load. Quieter at exercise. More components to service. Every Generac Protector is liquid-cooled.
Practical HC Reality
95% of Hunterdon County home installs are air-cooled Guardian units in the 18-26 kW range. That's the sweet spot for typical rural well-and-septic homes. Liquid-cooled Protector makes sense for larger properties or sustained commercial-scale loads.