What Size Generator Does an RV Need? Watts for the AC, 30 vs 50 Amp

What size generator runs an RV air conditioner?

Champion's method in its own manual is three steps: list what runs at the same time, total their running watts, then add the single highest starting wattage among them. Champion's operator's manual also tells you to start loads one at a time, largest first, so only one thing is starting at any moment.

Two generator makers put numbers on the air conditioner question. Cummins Onan specifies the built-in QG 4000 on gasoline to start one 13,500 BTU air conditioner with a 2,000 W base load at 500 ft and 100°F (38°C), and the QG 5500 to start two 15,000 BTU units with a 1,000 W base load at the same conditions. Honda says the 3,200 W EU3200i can power 13,500 BTU RV AC units, while noting that not all of its listed applications run at once.

Dometic's footnote is worth reading before you trust any of this: its generator figures come from what owners have experienced in real installations, the whole RV's power use has to be added in, and generators lose output at altitude and from poor maintenance.

What your RV actually draws

Amps from Dometic's 2021 rooftop manual and Coleman-Mach's Mach 3 Plus and Mach 15 product pages; watts from Furrion's Chill and microwave manuals, Norcold's Polar service manual and Progressive Dynamics' PD9245C page. Figures marked calculated are amps times volts, our arithmetic. Dometic's locked rotor amps are the compressor's stalled current at the instant of start, not a published "starting watts" rating.

What a 30 amp or 50 amp RV can draw

Jayco's towable owner's manual describes a 30 amp RV as running on one leg of 120 volt power with a maximum current flow of 30 amps, which works out to about 3,600 W (calculated, 120 V times 30 A). A 50 amp RV runs on two legs of 120 volt power at up to 50 amps per leg, so about 12,000 W in total (calculated). Jayco names 120/240 volt generator power for the 50 amp system.

Outlets are where buyers get caught. Champion fits an RV outlet it calls a NEMA TT-30R, but on model 201531 that outlet is rated 27.1 A, not 30 A. Honda's EU3200i has a 30 A twist lock instead, which an RV's TT-30 plug does not fit without an adapter. For 50 amp service, Champion's parallel kit 100319 carries a 14-50R, and the maker's own documents disagree about it: the kit manual says 240 V AC is not available, while the inverter product page describes a 120/240 V 50 A outlet. Read the kit's manual before you count on 240 V.

Soft starts and the compressor's surge

A soft start limits the current the compressor pulls at the moment it kicks in. Dometic's SmartStart manual says it reduces the starting current associated with the initial compressor startup, which reduces or eliminates flickering lights, brownouts and nuisance breaker trips, and rates the unit for a maximum of 15 starts per hour. Micro-Air says its EasyStart Breeze can cut start current by up to 75%.

Coleman-Mach claims up to a 75% cut in inrush amps and goes further than the others, saying a soft start also lowers power consumption while the air conditioner runs. That running claim is Coleman-Mach's alone among the sources here. No maker promises that a named generator will start a named air conditioner, and a soft start does nothing for a unit that cools poorly for other reasons, which is a separate problem.

Fitting a soft start means working inside the air conditioner's 120 volt electrical box. Dometic highly recommends a certified electrician for the job, and that is the right bar.

Inverter generator or open frame?

Inverter models are quieter and their makers publish a power quality figure. Champion's 201531 inverter is listed at 64 dBA from 23 feet with clean power under 3% THD; its 201279 open frame model is 68 dBA from the same distance, lists "Inverter: No" and publishes no THD figure. Honda puts the EU2200i at 48 to 57 dBA and says its inverter technology gives stable, clean power for computers and other sensitive equipment. Champion recommends UL1449 listed plug-in surge suppressors for sensitive electronics on any generator.

Two small inverters can be paralleled for more power: Honda lists up to 4,400 watts from two EU2200i units, using only a Honda approved parallel cable kit and only with the models it names. Champion's 200988 needs a kit too, model 100319. Overnight, many owners leave the generator off and run lights, a fan and a CPAP from the battery through an inverter sized for those loads.

Propane and altitude

Figures from Champion's manuals and product pages and Cummins Onan's QG 4000 and QG 5500 spec sheets. The loss depends on the model, so there is no single propane percentage: Champion keeps starting watts at 4,500 on both fuels for those two inverters but drops them from 5,300 to 4,780 on the open frame, and Onan rates the QG 5500 the same either way. Honda's EU2200i and EU3200i are gasoline only.

Altitude costs output on every one of them. Champion prints a drop of about 3.5% for each 1,000 ft of elevation and says adjusting the engine cannot change it. Onan prints the same 3.5% per 1,000 ft, measured from a 500 ft baseline, plus 1% for every 10°F rise in temperature. Honda states about 3.5% per 1,000 ft as a horsepower loss and wants a dealer carburetor modification above 5,000 feet.

Running a generator safely

Honda states it plainly: generator exhaust contains carbon monoxide, breathing it can kill you in minutes, and the machine runs outside only, far from windows, doors and vents, at least 3 feet from buildings. Champion adds that a portable must never run inside any enclosure, including the generator compartment of a recreational vehicle, nor in the back of a camper, trailer or truck bed, and keeps 5 feet clear of objects for fire. CPSC's 20 foot figure is written for a house, not an RV; treating it as a campsite minimum is our advice, not a published rule.

CO shutoff features help but do not replace an alarm. Honda's CO-MINDER shuts the engine down before CO near the generator gets dangerously high, and Champion says its CO Shield is not a substitute for an indoor carbon monoxide alarm. Cummins Onan's RV manual says never sleep in the vehicle with the set running unless the vehicle has a working carbon monoxide detector.

The start and stop sequence the makers give:

1. Check that the RV's carbon monoxide detector works (Jayco).
2. Turn the air conditioners and other appliances off before starting (Jayco).
3. Start the generator with no load and let it run a few minutes to stabilize (Champion).
4. Switch on the largest load first, then the rest one at a time (Champion).
5. Turn the air conditioners and large loads off before shutting it down (Jayco).

Where a park limits generator hours, as Joshua Tree does with three two hour windows a day, a battery bank topped up by solar panels covers the quiet gaps. Hours are set park by park, so check the campground you are booking.

One stop line, and it is ours rather than any maker's: wiring a generator into the RV's panel or fitting a transfer switch is a job for a licensed electrician or RV technician. Honda and Champion both say connections to a building's electrical system belong to a qualified electrician, and the isolation problem in an RV is the same.

Common questions