RV generators
Reading an Onan RV generator model number
The model number is on the serial number tag on the generator. The number at the front is the output (2.8 is 2,800 watts), the letters identify the series, and the last letter is the spec letter. To replace a unit, match the output, the fuel and the compartment dimensions.
What Cummins says about the model number
- Where it is. “Each Cummins Generator has a model/spec number description, which is shown on the serial number tag attached to the generator.”
- Every character counts. “Every character of the model number is significant. The last character of the model number is the specification letter which is important for obtaining the correct parts.”
- The leading number. Cummins does not define it in words, but in every Cummins rating table it matches the rated output: 2.8HGJBB is 2,800 watts, 2.5HGLAA is 2,500 watts, 4KYFA is 4,000 watts and 3.6KYFA is 3,600 watts.
Cummins does not publish what each of the series letters or the numeric suffix means, so we do not guess. What it does publish is which product each series code belongs to.
Series code to Cummins product
| Series in the model number | Cummins Onan product |
|---|---|
| HGJBB | QG 2800 / 2800 EVAP (and QG 2500 LP) |
| HGLAA | QG 2800i / 2500i LP |
| HGLBA | QG 4000i |
| KY | QG 4000 / 3600 LP (model codes KYFA and KYFR) |
| KV, KVC, KVD | Earlier QG 2500 LP, QG 2800 / 2800 EVAP, QG 2800 RM / 2500 RM LP |
| HGJAA | QG 5500 EFI / 7000 EFI |
| HGJAB | QG 5500 / 5500 EVAP / 5500 LP / 7000 / 7000 EVAP / 6500 LP |
So an HGJAA is not a small generator. If a listing or a search says “2.5HGJAA”, read the tag again: the 2,500 watt LP units Cummins lists are the 2.5HGJBB and the 2.5HGLAA.
Output and size to match when replacing
All of these are 120 volt, single phase. The size is length x width x height in inches.
| Model | Product | Fuel | Output | Size (in) | Weight | Sound | Cummins source |
|---|---|---|---|---|---|---|---|
| 2.8HGJBB-1120A | QG 2800 (HGJBB) | Gasoline | 2,800 W, 23.3 A | 22 x 16.3 x 12.8 | 125 lb | 70 dB(A) at 10 ft, half load | Spec sheet NAS-5501c-EN; operator manual A031C171 |
| 2.5HGJBB-1121A | QG 2500 LP (HGJBB) | LP vapor | 2,500 W, 20.8 A | 22 x 16.3 x 12.8 | 125 lb | 70 dB(A) at 10 ft, half load | Spec sheet NAS-5501c-EN |
| 2.8HGLAA-8311 | QG 2800i (HGLAA) | Gasoline | 2,800 W, 23.3 A | 22.0 x 16.3 x 13.4 | 113 lb | 66 dB(A) at 10 ft, half load | Spec sheet S-6773 (04/24) |
| 2.5HGLAA-8310 | QG 2500i LP (HGLAA) | LP vapor | 2,500 W, 20.8 A | 22.0 x 16.3 x 13.4 | 113 lb | 66 dB(A) at 10 ft, half load | Spec sheet S-6773 (04/24) |
| 4KYFA26100 | QG 4000 (KY) | Gasoline | 4,000 W, 33.3 A | 30.0 x 19.7 x 14.4 | 178 lb | 68 dB(A) at 10 ft, half load | Spec sheet A-1399p (8/15) |
| 3.6KYFA26120 | QG 3600 LP (KY) | LP vapor | 3,600 W, 30.0 A | 30.0 x 19.7 x 14.4 | 178 lb | 68 dB(A) at 10 ft, half load | Spec sheet A-1399p (8/15) |
| 4.0HGLBA-8305A | QG 4000i (HGLBA) | Gasoline | 4,000 W, 33.3 A | 30.0 x 20.3 x 14.0 | 149 lb | 66.5 dB(A) | Spec sheet S-6759 (04/24) |
Cummins’ own documents differ slightly on the HGLAA: operator manual A075S349 gives 110 lb and a width of 16.9 inches, the spec sheet 113 lb and 16.3 inches. Measure your compartment rather than relying on either.
Which one fits my coach?
- Read the tag. Note the full model number and the spec letter.
- Match the fuel. A gasoline coach takes a gasoline unit; an LP-fed one takes the LP model, which is rated lower (2,500 W against 2,800 W, 3,600 W against 4,000 W).
- Match the output. Going from a 2,800 W unit to a 4,000 W one changes the size class: the QG 4000 is 30 inches long against 22 for the QG 2800 family.
- Measure the compartment. Cummins publishes no drop-in statement between generations. Its mounting kit A043F935 is listed as a “retro adapter from KV”, the earlier series, and the HGLAA is 0.6 inch taller than the HGJBB on the spec sheets.
- Check the installation manual for the new model’s mounting, fuel and exhaust requirements before ordering.
The models we sell in these series
| Model | Fuel | Output | Cummins part | Price |
|---|---|---|---|---|
| 2.5HGLAA-8310 | LP Vapor | 2,500 W, 120 V | A074X612 | $4,730.72 |
| 2.8HGLAA-8311 | Gasoline | 2,800 W, 120 V | A074X611 | $4,436.53 |
| 3.6KYFA-26120 | LP Vapor | 3,600 W, 120 V | A055E865 | $5,026.73 |
| 4.0HGLBA-8306 | Gasoline | 4,000 W, 120 V | A073X541 | $4,604.64 |
| 4KYFA-6747 | Gasoline | 4,000 W, 120 V | A055E867 | $4,202.65 |
Prices are the Cummins suggested retail price, and RV generators ship nationwide. The full range, including the dual-fuel and QD diesel models, is on Cummins Onan RV generators.
Questions
Where is the model number on an Onan RV generator?
On the serial number tag attached to the generator, which Cummins also calls the nameplate or dataplate. It carries the model number and spec, the serial number, and the electrical ratings. Write the full model number down, including the letter at the end.
What does the last letter of the model number mean?
It is the specification letter. Cummins says every character of the model number is significant and that the last one is the spec letter, which is what decides the correct parts and the correct manual for your unit.
What is an Onan 2.5HGJAA?
Cummins does not list one. On the Cummins RV generator manuals page, HGJAA is the QG 5500 EFI and QG 7000 EFI series, and HGJAB is the QG 5500, 6500 LP and 7000 family. A 2,500 watt LP unit of the earlier QG 2800 generation is listed as the 2.5HGJBB-1121A, and the current one as the 2.5HGLAA. Check the tag: the letters after the number are what identify the series.
Will a 2.8HGLAA fit where my old 2.8HGJBB was?
Compare the numbers before you buy. Cummins gives the HGJBB as 22 x 16.3 x 12.8 inches and the HGLAA as 22.0 x 16.3 x 13.4 inches, so the HGLAA is 0.6 inch taller on those sheets. Cummins does not publish a drop-in statement, and its mounting kit A043F935 is described as a retro adapter from the older KV series. Measure the compartment and check the fuel, the mounting and the exhaust routing against the installation manual.
What is a 4KYFA?
The Cummins Onan QG 4000, a 4,000 watt, 120 volt gasoline generator rated at 33.3 amps. The LP version is the 3.6KYFA at 3,600 watts. The 4KYFA-6747 we sell is $4,202.65.
Sources, read 9 October 2026: the Cummins RV generator manuals page (series and product names, and the serial number tag quote); Cummins operator manuals A031C171 (HGJBB), A041D131 (KY), A035D009 (HGJAA/HGJAB) and A075S349 (HGLAA), each section 2.3 or 5, for the model identification quote; Cummins spec sheets NAS-5501c-EN (QG 2800, HGJBB), S-6773 (QG 2800i, HGLAA), A-1399p (QG 4000, KY) and S-6759 (QG 4000i, HGLBA) for ratings, sizes, weights and sound; Cummins RV accessory catalog, bulletin 6646901 (mart.cummins.com), for mounting kit A043F935. Prices and part numbers from the 2026 Cummins RV price sheet.
Not sure what is on your tag?
Send us the model number and spec letter and we will tell you which current Cummins unit matches it, before you order.
Rather just talk to someone?
Leave a number and we will call you. No sales script, no obligation.
Got it. We will call you. If you would rather not wait, ring (214) 957-4307 and ask for whoever is on generators.