Cummins Onan RV generators, explained
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Quick answer
Cummins Onan makes the built-in generators found in many motorhomes and towables. Pick by RV type and air conditioners. Cummins' 2025 catalog lists the QG 2800i at 2.8 kW for Class B RVs and truck campers, running one 13,500 BTU AC. The QG 4000i is listed at 4.0 kW for one 15,000 BTU AC. The QG 5500 and 7000 run two ACs. The QG 5500's spec sheet lists about 0.6 gallons of gasoline an hour at half load. It says the unit meets the National Park Service limit of 60 dB(A) at 50 feet.
Which Onan fits which rig
Cummins' 2025 RV generator catalog groups its gasoline models like this:
| Model | Continuous power | Intended RV | Air conditioners |
|---|---|---|---|
| QG 2800i / 2500i LP | 2.8 / 2.5 kW | Class B, truck campers | One 13,500 BTU |
| QG 4000i | 4.0 kW | Class C and towables | One 15,000 BTU |
| QG 5500 / 7000 EFI | 5.5 / 7 kW | Travel trailers, fifth wheels, Class A or C | Two 13,500 BTU (5.5 kW) or two 15,000 BTU (7 kW) |
The catalog lists the QG 2800i and 4000i as inverter-based with variable speed and 63 dB at no load. If you are replacing a unit, start with the model and spec number on its nameplate, since mounting, fuel lines and controls differ.
QG 5500 by the numbers
Cummins' QG 5500 specification sheet lists:
- Output: 5,500 W at 120 V, 45.8 A, on gasoline or LP vapor.
- Size and weight: 288 lb. 33.6 by 22.2 by 16.7 inches.
- Sound: 69 dB(A) at 10 feet, half load. Cummins says it meets the National Park Service requirement of 60 dB(A) at 50 feet.
- Warranty: 3-year limited.
- Operating range: -20 to 120 degrees F on gasoline, 0 to 120 degrees F on LP.
Fuel use:
| Load | Gasoline | LPG |
|---|---|---|
| No load | 0.3 gal/h | 0.4 gal/h |
| Half load | 0.6 gal/h | 0.8 gal/h |
| Full load | 0.9 gal/h | 1.1 gal/h |
Heat and altitude cut power
The QG 5500 sheet rates output at 77 degrees F and 500 feet of altitude. It says output falls about 1% for every 10 degrees F hotter, and about 3.5% for every 1,000 feet higher. At 5,500 feet, that is roughly 17.5% less, or about 4,540 watts from a 5,500 watt unit. Mountain travelers running two air conditioners should keep that in mind.
Fuel and emissions rules for towables
Gasoline Onan units are plumbed to the RV's fuel system, and LP models to its propane tank. Two details from Cummins' paperwork matter when you buy or replace one:
- Evaporative emissions. The QG 5500 sheet says that since January 1, 2011, gasoline generator sets on trailers, diesel chassis or other non-motorized mobile apparatus must use an EVAP generator set, approved tank, EVAP canister, hoses and fittings meeting CARB Tier 3 and EPA phase 3 standards. It says this applies in all 50 states. So a towable needs the EVAP-capable spec, not just any 5500.
- Cold-weather LP. The sheet rates LP operation from 0 degrees F, and says LP performance depends on tank capacity, surface area and the butane content of the gas.
The 2025 catalog lists the QG 2800i and QG 4000i as CARB 2024 certified with fuel injection, and the QG 2800i with a single fuel line.
Keep it running between trips
A generator that sits all season can fail when you need it, at camp or during a power outage at home. Follow the exercise and service schedule in your owner's manual: oil, air filter and spark plug on time. Buy parts by your exact model and spec number, because Cummins builds several variants of each size with different breakers and fuel setups. The QG 5500 sheet, for example, lists six spec numbers, split by fuel and breaker layout. If your RV lacks a built-in unit, a portable inverter with a TT-30R outlet can serve a 30 amp rig instead. See our RV generator guide.
What to look for when you buy
Onan maintenance kit matched to your model
Best for: Owners servicing a QG 2800i, 4000, 5500 or 7000
Built-in Onan units are model-specific. Kits matched to your spec number keep oil, air filter and spark plug service on schedule.
Watch out: Confirm the spec number on the generator's nameplate before ordering.
See options on Amazon (opens Amazon in a new tab)Portable inverter with TT-30R for RVs without a built-in unit
Best for: 30 amp towables and older rigs
A portable inverter avoids an installed system while still running one roof AC if it is sized right.
Watch out: Keep it away from windows, vents and neighbors, and mind park sound rules.
See options on Amazon (opens Amazon in a new tab)RV carbon monoxide alarm
Best for: Any RV with a generator
Built-in generators exhaust right beside the coach, so an RV-rated CO alarm inside is basic protection.
Watch out: Test before every trip, and replace it on the maker's schedule.
See options on Amazon (opens Amazon in a new tab)Questions people ask
- What size Onan generator do I need?
- Match it to your air conditioners. Cummins lists the QG 2800i for one 13,500 BTU AC, the QG 4000i for one 15,000 BTU AC, and the QG 5500 or 7000 for two ACs.
- How much gas does an Onan 5500 use?
- Cummins' spec sheet lists about 0.3 gallons an hour at no load, 0.6 at half load and 0.9 at full load on gasoline.
- Is an Onan generator quiet enough for national parks?
- Cummins says the QG 5500 meets the National Park Service sound limit of 60 dB(A) at 50 feet. Parks may still set generator hours.
- Why does my Onan generator lose power in the mountains?
- Thinner air. The QG 5500 sheet says output drops about 3.5% per 1,000 feet of altitude and about 1% per 10 degrees F of heat.
- Does a travel trailer need a special Onan generator?
- For gasoline units, yes. Cummins says gasoline generator sets on trailers and other non-motorized mobile apparatus must be EVAP-compliant under CARB Tier 3 and EPA phase 3 rules, in all 50 states.
Sources
- Cummins Onan RV & Commercial Mobile Generator Accessory Catalog (2025), Cummins
- RV QG 5500 Specification Sheet, Cummins
- 36 CFR 2.12 Audio disturbances, Code of Federal Regulations (via Cornell LII)