| Quick Facts | |
|---|---|
| 13,500 BTU RV AC running watts | roughly 1,400-1,700 W |
| 15,000 BTU RV AC running watts | roughly 1,600-1,800 W |
| Typical compressor startup surge | about 2-3x running watts, for 1-2 seconds |
| 30-amp RV service theoretical max | 3,600 W (120V x 30A) |
| DOE CEER range, 12,000 BTU/h room AC, best vs. less efficient | 15.4 CEER (~779 running W) vs. 10.9 CEER (~1,101 running W) |
| OSHA generator clearance for ventilation | 3 to 4 feet on all sides and above |
How many watts to run an RV air conditioner, by BTU size
A 13,500 BTU rooftop unit, the size on most travel trailers, draws roughly 1,400 to 1,700 running watts; a 15,000 BTU unit runs closer to 1,600 to 1,800.
Shopping for a specific model? See our full rv generator roundup — 10 models compared on the specs that decide it.
How many watts to run an RV air conditioner comes down mostly to BTU rating once the compressor is already spinning. A compact 9,000 to 11,000 BTU unit typically pulls somewhere around 700 to 1,000 running watts. The 13,500 BTU size, the one bolted to the roof of most travel trailers and smaller motorhomes, runs closer to 1,400 to 1,700 watts once it settles into a steady cooling cycle. Step up to a 15,000 BTU unit, more common on larger fifth wheels, and that running draw climbs to roughly 1,600 to 1,800 watts.
None of those figures are published by a federal agency specifically for RV rooftop units, worth saying plainly rather than dressing them up as more official than they are. The Department of Energy does publish exactly this kind of math for window and portable room air conditioners, though, and the underlying physics is identical: efficiency, rated as CEER (Combined Energy Efficiency Ratio), tells you how many watts a given BTU rating actually costs. DOE's Federal Energy Management Program lists 8,000 to 13,999 BTU/h room units at anywhere from 15.4 CEER for the best available model down to 10.9 CEER for a less efficient one, which works out to roughly 779 running watts on the efficient end and 1,101 watts on the inefficient end for the identical 12,000 BTU of cooling. Buy the less efficient compressor and the wattage bill for the same cooling output can climb by 300-plus watts.
Why the starting surge matters more than the running watts
The running-watts number rarely strands anyone; the startup surge does, since a compressor can briefly demand two to three times its running draw before settling down.
Running watts describe the AC once it's already on. Getting it there is a different problem. Every compressor motor pulls a locked-rotor surge for a fraction of a second as it starts spinning from a dead stop, commonly two to three times the running wattage before it settles into its normal draw. A 13,500 BTU unit running at 1,500 watts might briefly demand 3,000 to 4,500 watts on startup, gone again within a second or two, but that spike is exactly what a marginal generator can't ride through.
This is the part of the math that trips people up on a shopping trip. A generator rated at 2,000 running watts looks comfortably above a 1,500-watt running load, so it seems like it should work. It often doesn't, because the spec sheet's peak or surge rating, not the running-watt number, is what determines whether the compressor gets past that first half-second. Check both numbers on any generator being sized against an RV AC, not just the one that looks reassuring.
What size generator do you need to run an RV air conditioner
Most 13,500 BTU rooftop units need a generator rated at least 3,000 running watts with real surge headroom; a 15,000 BTU unit is safer paired with 3,500 to 4,000 watts.
Put the running load and the startup surge together and a practical sizing range falls out. A single 13,500 BTU RV air conditioner generally wants a generator rated at least 3,000 running watts, with a peak or surge rating comfortably above that to absorb the compressor's opening spike. A 15,000 BTU unit is safer paired with something in the 3,500 to 4,000-watt class. Those numbers assume the AC is the only major load starting at that moment, which isn't always true in a rig running a fridge or microwave off the same circuit.
RV electrical service factors into this too. A 30-amp RV hookup is rated for a theoretical maximum of 3,600 watts, 120 volts times 30 amps, which lines up closely with the low end of what a 13,500 BTU AC needs and explains why 30-amp rigs are usually built around one AC rather than two. A 50-amp service splits its capacity across two 120-volt legs instead, giving considerably more headroom for a second AC unit or heavier simultaneous loads. Our RV generator buying guide breaks down generator sizing by amperage and BTU load if you're matching a unit to your exact rig rather than working from these general ranges.
Running the air conditioner alongside everything else in the RV
An AC rarely runs alone. Add a fridge, microwave, or charging electronics and the generator needs headroom beyond the AC's number alone, and OSHA's own safety guidance is explicit about not pushing past a generator's rated capacity.
An RV air conditioner is almost never the only thing drawing power at once. A residential-style RV fridge, a microwave running for a few minutes, device chargers, and the water pump all add their own running watts on top of the AC's load, and that combined total is what actually sets the safe minimum generator size, not the AC number in isolation. Tallying every circuit that might run at the same time and sizing up rather than sizing to the edge is a more reliable approach than borrowing rough 'how many watts to power a house generator' rules of thumb from home backup planning, which assume a very different load profile.
The Occupational Safety and Health Administration's own generator safety guidance is direct on this point: do not overload a generator, since pushing it past its rated capacity risks overheating that can become a fire hazard, not just a tripped breaker. The same guidance calls for keeping 3 to 4 feet of clear space on all sides and above a running generator for adequate ventilation, a detail that matters as much for a unit wedged into an RV's storage bay or crammed against an awning as it does for one running in a backyard. Our portable generator guide compares models by rated and surge wattage if the AC is one of several loads you're sizing for rather than the only one.
Soft starts and other ways to shrink the wattage you need
A soft-start device smooths the compressor's startup surge, often cutting the peak demand enough to run the same AC on a meaningfully smaller generator.
The starting surge is the one number in this whole equation that's actually negotiable. A soft-start device, wired into the AC's compressor circuit, ramps the motor up gradually instead of letting it jump straight to full current on startup, which cuts the locked-rotor spike considerably compared with a compressor starting the normal way. That's the difference between needing a generator sized for the surge and needing one sized closer to the plain running watts, a meaningfully smaller and lighter unit to carry and fuel.
It isn't a free upgrade, though, worth saying honestly. A soft start adds installation cost and complexity, does nothing to the AC's steady running wattage, and some manufacturers' warranty terms carry specific requirements around approved soft-start hardware. For anyone boondocking or generator-camping regularly with a single AC and no interest in hauling a larger unit than necessary, it's one of the more effective single upgrades available. For anyone running two rooftop units or planning to add appliances later, it buys headroom rather than solving the sizing problem outright.
So, how many watts do you actually need
Match the generator to both numbers, the AC's running watts and its startup surge, then add real headroom for whatever else runs off the same circuit.
There isn't one number that answers how many watts to run an RV air conditioner for every rig, but there is a reliable way to land on the right one. Start with the AC's running watts, add its startup surge or confirm a soft start handles that spike instead, then stack on whatever else genuinely runs at the same time; the fridge cycling on mid-cooling matters more than it seems like it should. Sizing a generator to the running watts alone is the single most common mistake, and it shows up as a stalled compressor rather than a slow one.
Check the AC's own nameplate for its actual running and, if listed, locked-rotor amp ratings before assuming any of the ranges above apply exactly to your unit, since manufacturers vary. Our RV generator hub rounds up the sizing math, fuel-type tradeoffs, and noise considerations that go into choosing a generator built around AC use rather than light weekend loads.