Cummins Onan P2500i vs Generac #8251 GP2500i

Comparison Overview

Key takeaways

• Both deliver 2200 running watts and 2500 starting watts in compact inverter designs.
• Cummins Onan P2500i runs 10 hours at 25% load and 8 hours at 50%.
• Generac #8251 GP2500i runs 8 hours at 25% load and 4.5 hours at 50%.
• Both weigh 48 lb, making them similarly portable for camping and outages.
• Cummins Onan P2500i lists 52 dB noise, Generac noise rating is not provided.

Best use cases

Choose the Cummins Onan P2500i if you want fewer fuel stops and longer stretches of hands off power. Its 10 hour runtime at 25% load and 8 hours at 50% is a practical advantage for camping weekends, tailgates, and overnight home backup where you would rather not refuel in the dark. It is also a good fit for RV style needs like battery charging, running a TV, router, fans, or a small microwave in short bursts, as long as you stay within 2200 running watts. With a published 52 dB rating, it is also easier to shop for if quiet operation is a priority, even though real world noise still depends on load and distance.

Choose the Generac #8251 GP2500i if you want the same compact power level and weight, but you are typically using it in shorter windows or lighter duty situations. At 8 hours at 25% load, it can still cover an evening at camp or a few hours of outage support, and the identical 2200 running watts and 2500 starting watts means it should handle the same categories of appliances. The tradeoff is that the 4.5 hour runtime at 50% load suggests more frequent refueling if you run a steadier load, like a fridge plus fans and device charging, for long stretches.

For job site use, both are better suited to smaller tools and intermittent loads than high draw equipment. For home backup, either can keep essentials going, but neither is a whole house solution, plan your loads and consider extension cord management and safe outdoor placement.

Verdict & recommendation

If your priority is longer runtime per tank for camping, RV support, or overnight outage coverage, the Cummins Onan P2500i is the more compelling pick on paper, especially at 50% load where it is rated for 8 hours versus 4.5 hours. If your priority is simply getting a compact 2200 running watt inverter generator at 48 lb and your typical sessions are shorter or lighter load, the Generac #8251 GP2500i can make sense since the core power output is essentially the same.

Because the Generac noise spec is not listed here, noise sensitive buyers should verify real world sound levels before deciding. In the end, choose based on how long you need to run between refuels, and how much certainty you want around published noise performance.