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A campsite at dusk with a dead phone and an air conditioner that will not start is the wrong place to learn that a generator is too small. To size generator for RV use, add the running watts of the loads you plan to run at the same time, check the starting watts of the largest motor load, and match the RV outlet on the panel. The steps below work through each figure with watts and run times from current listings.
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How to size generator for RV: the quick answer
The short version runs like this. Add the running watts of every load you plan to run at the same time. Compare that total with the running watts on the listing, and compare the largest starting load with the peak watts. Then check that the panel has the RV outlet your cord needs. The Oxseryn 4400 lists 3400 running watts and 4400 peak watts with a 30A RV port, the PowerSmart 3800 (on Amazon) lists 3200 running watts and 3800 starting watts with a 120V 30A outlet, and the Westinghouse lists 9500 running watts and 12500 peak watts on gas with a 50A RV-ready outlet.
Step 1: Add the running watts
Running watts are what a load draws while it runs. Peak watts, also called starting watts, are the short spike a motor draws when it starts. A generator must cover the running watts of all the loads at the same time, plus the starting spike of the largest motor. The table below shows the running and peak watts from the listings used here, so you can see the size classes side by side.
| Unit | Running watts | Peak watts |
|---|---|---|
| Oxseryn 4400 | 3400 | 4400 |
| PowerSmart 3800 | 3200 | 3800 |
| Westinghouse 12500 | 9500 on gas, 8500 on propane | 12500 on gas, 11200 on propane |
List the loads you plan to run at the same time: air conditioner, microwave, fridge, lights and phone chargers are the usual RV loads. Add their running watts from their own labels, then leave headroom above the total. If the total sits near the running watts of a unit, move up a size class rather than running a generator at its limit all day.
Step 2: Check starting watts for motors
Motors pull more at startup than they use while running, and the air conditioner is the load that decides the size. The peak watts on the listing must cover that startup spike plus the running watts of the loads already on. The Oxseryn 4400 lists 3400 running watts and 4400 peak watts, the PowerSmart 3800 lists 3200 running watts and 3800 starting watts, and the Westinghouse lists 9500 running watts and 12500 peak watts on gas. That gap between running watts and peak watts is the room for a motor to start. If the air conditioner still will not start, turn off the loads you do not need and try again with the heavy loads off.
Step 3: Match the RV outlet
The outlet on the panel must match the cord on the RV. The Oxseryn 4400 lists a 30A RV port, and the second Oxseryn 4400 listing repeats the same 30A RV port with 2 120V AC ports and 1 12V DC port. The PowerSmart 3800 lists a 120V 30A L5-30R twist-lock outlet. The Westinghouse lists a 120V L14-30R 30A outlet and a 120/240V 14-50R 50A RV-ready outlet. If your RV cord is a 30A cord, a 30A RV outlet is the fit; if it is a 50A cord, look for the 50A outlet. See the best L5-30 generator adapters for RV if the plug shapes do not match.
Step 4: Check run time, fuel and noise
A generator that fits on watts still has to run long enough. The Oxseryn 4400 runs up to 14 hours at 25% load with ECO mode on a 2 gallon tank, and the Westinghouse runs up to 12 hours. ECO mode lets the engine slow down at light load, which stretches a tank. Noise matters at a campsite: the PowerSmart states 59 dBA from 23 feet away and the Oxseryn 4400 states under 72 dBA from 23 feet away. Weight matters too when you load the unit in and out of a bay: the PowerSmart weighs 47 lb and the Oxseryn 4400 weighs 56 lb. Fuel generators run outdoors only, far from doors and windows, because of carbon monoxide.
Tips for RV use
- Read the watt label on the air conditioner and the microwave before you buy, since those are the loads that decide the size.
- Start the largest motor load with the other loads off, then add the rest one at a time.
- Keep the fuel gauge in view: the Oxseryn 4400 lists a fuel gauge on its 2 gallon tank.
- The Oxseryn 4400 listing names overload protection and low oil shutdown, which shut the unit down before damage.
- The Westinghouse lists remote start with a key fob, electric start and recoil start.
FAQ: power away from the grid
What size generator do I need for an RV?
Add the running watts of the loads you plan to run at the same time and compare the total with the running watts on the listing. The Oxseryn 4400 lists 3400 running watts, the PowerSmart 3800 lists 3200 running watts and the Westinghouse lists 9500 running watts on gas.
What size generator runs an RV air conditioner?
Check the starting watts on the air conditioner label and compare them with the peak watts on the listing. The Oxseryn 4400 lists 4400 peak watts, the PowerSmart 3800 lists 3800 starting watts and the Westinghouse lists 12500 peak watts on gas. Start the air conditioner with the other loads off.
Is a 30A outlet enough for an RV generator?
It depends on the RV cord. The Oxseryn 4400 lists a 30A RV port and the PowerSmart 3800 lists a 120V 30A outlet, while the Westinghouse lists a 120/240V 14-50R 50A RV-ready outlet for a 50A cord.
How long will a generator run an RV?
It depends on the tank and the load. The Oxseryn 4400 runs up to 14 hours at 25% load with ECO mode on a 2 gallon tank, and the Westinghouse runs up to 12 hours.
Related solar guides
See every Power Stations and Generators guide and all Inverter and Dual Fuel Generators guides. For picks, see the best generator for fifth wheel roundup and the best RV generator for travel trailers roundup.
