What size generator for an RV air conditioner?
A 13,500 BTU rooftop unit runs about 1,500 watts and starts near 3,000, so a 3,400W inverter covers it alone. Fit a soft starter and the start drops to 2,025W, which slips under a 2,200W suitcase inverter's peak, the trick behind running rooftop AC on the small units. The number that sizes the generator is the start surge, and the table below has it for each common BTU, bare and softened.
Run, surge, and soft-start watts by BTU
| Rooftop unit | Running | Start (bare) | Start (soft) | Inverter, bare | Inverter, soft start |
|---|---|---|---|---|---|
| 9,200 BTU (compact / pop-up rooftop) | 1,100 W | 2,200 W | 1,485 W | 2,200W inverter | 2,200W inverter |
| 13,500 BTU (standard rooftop) | 1,500 W | 3,000 W | 2,025 W | 3,400W inverter | 3,400W inverter |
| 15,000 BTU (high-output rooftop) | 1,800 W | 3,500 W | 2,395 W | 3,500W portable | 3,400W inverter |
The two class columns are the smallest inverter that starts the AC with 20% running headroom, without and with a soft starter. A soft starter is the cheapest way to buy a class of margin, and on a 15,000 BTU unit it drops the answer from a 3,500W portable to a 3,400W inverter.
Why the surge, not the run, decides this
A rooftop AC compressor is a sealed induction motor, and starting one is the whole sizing event. Running, a 13,500 BTU unit is a 1,500W load any inverter shrugs off. Starting, it pulls double that for a fraction of a second, and a generator that can't deliver the spike sags its voltage, the AC's overload trips, and it retries a minute later. A soft starter ramps the compressor up instead of slamming it, cutting the start by about a third, which is why it earns its cost on a rig sized close.
The 30 amp shore cord caps everything at 3,600W regardless of the generator, so a unit bigger than the 3,400 to 3,500W classes carries watts you can't draw through one AC and a 30 amp rig. Match the generator to the AC plus the loads that run beside it, and let the cord settle any urge to go bigger. The full-rig math lives in the RV calculator.
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Questions people ask
What size generator do I need for a 13,500 BTU RV air conditioner?
A 3,400W inverter starts and runs a 13,500 BTU rooftop unit on its own; with a soft starter the softened 2,025W start fits a 2,200W suitcase inverter's peak, which is how owners run one on the small units. Neither figure includes the converter, fridge, or microwave, so plan the whole load, not the AC alone.
Does a soft starter really let a smaller generator run an RV AC?
Yes. A 13,500 BTU unit starts at about 3,000W bare and roughly 2,025W with a soft starter, a drop of about a third. That is the difference between needing a 3,400W inverter and squeaking the start under a 2,200W unit's peak. It cuts the start slam, not the running watts, so continuous headroom still wants the larger class if the AC runs for hours.
Can two RV air conditioners run on one generator?
Only a big one, or paralleled inverters. Two rooftop units together is 50 amp RV territory, roughly 3,300 running watts before the converter and fridge, with two start surges to cover. That is a job for a large inverter or a paralleled pair, and it is covered on the 50 amp RV page.