For the supplied reference setups, plan for 1,222 W running and 977 W starting with no rooftop AC, 3,409 W running and 3,952 W starting with a 13,500 BTU AC, or 3,642 W running and 4,627 W starting with a 15,000 BTU AC. In the two AC setups, starting capability is the decisive requirement. These presets are not a universal size for every 30 amp RV; your generator must meet both ratings for the loads you actually plan to run together.
How running watts, starting watts, and 30 amp service fit together
A generator has two relevant power limits:
- Running capacity supports equipment after it is operating normally.
- Starting capability, sometimes called surge capacity, supports the brief extra demand when a motor such as an air-conditioner compressor starts.
For this comparison, 30 amp RV service means one 120 V leg and 3,600 W nominal. That describes the RV's nominal shore-power service; it is not, by itself, a generator-size recommendation. The supplied service assessment compares modeled running watts with 3,600 W only. It does not check current, power factor, breaker behavior, voltage drop, connector compatibility, wiring condition, or installation safety.
All three modeled running loads are below the nominal service figure. However, an AC compressor can require more power while starting. That is why the 13,500 BTU preset needs 3,952 W of generator starting capability even though its modeled running load is 2,727 W, and the 15,000 BTU preset needs 4,627 W starting even though its modeled running load is 2,913 W. In both AC presets, the starting requirement is higher than the recommended generator running capacity and therefore becomes the decisive generator constraint.
The recommended running figures include the preset's planning headroom. For example, the 15,000 BTU setup has a modeled running load of 2,913 W but recommends 3,642 W of generator running capacity. That recommended capacity being slightly above 3,600 W does not mean the RV is modeled as drawing that much. It is the generator capacity planned under this preset's assumptions.
Worked example: three 30 amp RV setups
| Reference setup | Modeled running load | Recommended generator running capacity | Generator starting capability | Decisive rating |
|---|---|---|---|---|
| No rooftop AC | 977 W | 1,222 W | 977 W | Running capacity |
| 13,500 BTU rooftop AC | 2,727 W | 3,409 W | 3,952 W | Starting capability |
| 15,000 BTU rooftop AC | 2,913 W | 3,642 W | 4,627 W | Starting capability |
The no-AC setup has the lowest generator requirements when rooftop cooling is not needed. Adding either AC raises the steady load, but the larger sizing effect is the short starting demand. If a generator meets the recommended running figure but not the starting figure, the AC setup does not pass this planning check.
These presets assume one motor starts at a time and use a 0.80 running-load planning policy. Those are assumptions for these calculations, not universal electrical rules. If two motor-driven appliances may start together, or if your RV has loads not represented by the preset, enter your actual loads and operating schedule in the calculator.
Common sizing mistakes
Treating “30 amp” as the generator size
The 30 amp label describes the RV's nominal electrical service, not the watt ratings your generator should have. Compare the generator's continuous rating with the recommended running requirement and its applicable surge rating with the starting requirement.
Checking running watts but ignoring the AC start
The modeled running loads for both AC presets are below the nominal 3,600 W service figure, but their generator starting requirements are higher than 3,600 W. Running and starting are separate checks, and both matter when selecting a generator.
Confusing power with trip energy
Watts describe the rate at which an appliance uses power. Trip energy depends on both power and operating time and is expressed in watt-hours (Wh) or kilowatt-hours (kWh). This page does not calculate trip energy, fuel use, or runtime.
Entering zero for an unknown appliance
Unknown is not zero. If you do not know an appliance's power requirement, check its nameplate or manual. Record both running and starting watts when the manufacturer provides them.
Assuming a soft starter guarantees a smaller generator
A soft starter may change an AC's starting behavior, but the supplied data does not quantify a reduced starting requirement. Do not reduce the planned generator size unless applicable AC and soft-starter manufacturer information supports the change for your equipment. Then rerun the calculation with the supported starting value and your actual load plan.
Check your own RV in the calculator
- List the essential loads. Include the rooftop AC, converter or charger, refrigerator mode, lights, and other equipment you need during the same period.
- Separate optional loads. Decide whether higher-power items used for cooking or heating can take turns with the AC instead of operating at the same time.
- Read the ratings. Check each appliance nameplate or manual for running watts and, for motor loads, starting or surge watts. Do not replace an unknown rating with zero.
- Enter the loads in the RV Generator Size Calculator. Use that result rather than treating one of these presets as your RV's specification.
- Check the generator details. Compare continuous and surge ratings separately. Also verify voltage, output connection, and manufacturer conditions for your RV setup; this page does not perform those compatibility checks.
For a closer look at the planning ranges behind the two rooftop AC sizes, see How Many Watts Does an RV Air Conditioner Use?.
Limits of the preset comparison
The three setups are calculator presets, not measurements of your RV or specifications for a particular generator. The air-conditioner values are planning typicals with ranges, so the actual model nameplate or manufacturer documentation should supply the load entered for your RV.
This comparison does not select a generator model or evaluate its receptacle, adapter, fuel consumption, noise, price, or runtime. It also does not guarantee breaker, connector, or wiring suitability. Use the figures as a planning screen, then confirm the generator and RV requirements in their manufacturer documentation.