What size generator do I need to run a 13,500 BTU RV air conditioner?

At minimum, a generator rated for at least 3,000W starting watts if nothing else is running at the same moment the compressor starts. In practice most rigs have other loads such as the converter or a fridge running too, so a 3,500W to 5,000W generator without a soft starter, or a 2,000W to 3,000W generator with one fitted, covers the common real-world scenarios shown in the tables above.

Why is my needed generator size so much bigger than the air conditioner's running watts?

Because a generator has to survive the brief startup surge, not just the steady running load. A 13,500 BTU unit runs at about 1,400W but surges to roughly 3,000W for a fraction of a second at startup, and the generator's starting watts rating, not its continuous running watts rating, is the number that has to cover that surge.

Does a soft starter really let me use a smaller generator?

Yes, often by a meaningful margin. Cutting a 13,500 BTU air conditioner's 3,000W startup surge to roughly 1,200W with a soft starter can drop the required generator class from 5,000W down to 3,000W in a scenario with 1,800W of other loads running, based on the table above. That is often one or two standard generator size classes smaller, and a soft starter typically costs less than the price difference between those classes.

Can I run two RV air conditioners off one generator?

Only if the generator's starting watts rating covers both units' running watts plus the larger of the two units' startup surge, assuming the two compressors do not start at exactly the same instant. Run your specific combination of running loads and the larger unit's surge through the generator size calculator rather than assuming a published figure covers a two-unit scenario, since none of the figures on this page assume two compressors.

What generator wattage does a 30 amp RV pedestal roughly replace?

A 30A RV shore power service is rated at 3,600VA, a published NEMA TT-30 figure. That is a useful rough comparison point, though a generator's starting watts rating and a pedestal's continuous VA rating are not measuring quite the same thing, since the pedestal has no equivalent startup surge limitation of its own the way a generator does.

Is starting watts or running watts the number on a generator's price tag and marketing?

Generator marketing usually leads with the larger starting watts figure, since it is the bigger number, while the continuous running watts rating is typically listed lower in the specifications and is meaningfully smaller. Both figures matter for different reasons: starting watts decides whether a compressor-driven load will start at all, and running watts decides what the generator can sustain once everything is already running.

Reference

RV Generator Sizing Chart by What You Want to Run

Researched from published standards and manufacturer specifications. Updated 2026-09-17.

Quick answer

A generator is sized by the largest startup surge plus everything else running, not by running watts alone. About 1,800W of other loads plus a 13,500 BTU air conditioner's 3,000W startup surge needs 4,800W of starting capacity, which is why the WEN 56477i's 4,800W rating lines up almost exactly with that common scenario. A soft starter cutting the surge to about 1,200W drops the same scenario to a 3,000W-class generator, often one or two size classes smaller.

Generator sizing gets confused with running watts constantly, but a generator that comfortably covers a rig's steady running loads can still fail to start an air conditioner if its starting watts rating is not also checked against the compressor's surge. The formula is straightforward: total running watts for everything else on the generator, plus the single largest startup surge, has to fit within the generator's rated starting watts. That surge is almost always the air conditioner compressor.

The tables below run that formula across common combinations of other loads and air conditioner size, both with and without a soft starter fitted, then flip the question around to show how much headroom is left in each standard generator size class, and finally check four specific published generator models against the same numbers.

Generator starting watts needed, by other loads and air conditioner size

Other loads is everything running besides the air conditioner at the moment it starts, such as the converter, lights, and a fridge. Buy size rounds up to the next standard generator class this site's calculator recognizes: 2,000, 2,200, 3,000, 3,500, 4,000, 4,500, 5,000, 6,000 or 7,000W.

Generator size needed for common load combinations, without and with a soft starter
Other loads	Air conditioner	AC startup surge	Needed, no soft starter	Buy, no soft starter	Needed, with soft starter	Buy, with soft starter
0W	13,500 BTU	3,000W	3,000W	3,000W	1,200W	2,000W
0W	15,000 BTU	3,500W	3,500W	3,500W	1,400W	2,000W
800W	13,500 BTU	3,000W	3,800W	4,000W	2,000W	2,000W
800W	15,000 BTU	3,500W	4,300W	4,500W	2,200W	2,200W
1,800W	13,500 BTU	3,000W	4,800W	5,000W	3,000W	3,000W
1,800W	15,000 BTU	3,500W	5,300W	6,000W	3,200W	3,500W

Convention Source: Needed watts = other loads + AC startup surge (or surge x 0.4 with a soft starter, a convention). AC startup surge figures are typical published values for the BTU class.. This matches the exact math behind this site's generator size calculator and air conditioner startup load calculator.

How much headroom does each standard generator size leave for a 13,500 BTU air conditioner?

Headroom here is starting watts minus the 13,500 BTU air conditioner's own surge, which is what remains for every other load running on the generator at the moment the compressor kicks on. A negative number means that generator class cannot start this air conditioner at all without a soft starter.

Headroom for other loads, by generator size, 13,500 BTU air conditioner
Generator size	Headroom, no soft starter	Headroom, with soft starter
2,000W	-1,000W (cannot start)	800W
2,200W	-800W (cannot start)	1,000W
3,000W	0W	1,800W
3,500W	500W	2,300W
4,000W	1,000W	2,800W
4,500W	1,500W	3,300W
5,000W	2,000W	3,800W
6,000W	3,000W	4,800W
7,000W	4,000W	5,800W

Convention Source: Generator size minus the 13,500 BTU air conditioner's published startup surge (3,000W), or minus the soft starter convention figure (1,200W).

Four published generator models against the same numbers

These are the published starting watts ratings from the specific generator listings, checked against the same 13,500 BTU air conditioner surge used throughout this page.

Published generator models, headroom for a 13,500 BTU air conditioner
Generator	Starting watts (published)	Headroom, no soft starter	Headroom, with soft starter
WEN 56477i 4,800W	4,800W	1,800W	3,600W
WEN 6800W Dual Fuel	6,800W	3,800W	5,600W
ERAYAK 4,500W Dual Fuel	4,500W	1,500W	3,300W
Pulsar PGD40ISCO 4,000W	4,000W	1,000W	2,800W

Published standard Source: Manufacturer published starting watts ratings on the product listings, current at time of writing.

Why running loads add together but a single surge usually does not

The formula behind every table on this page treats other running loads as additive, because a converter, a fridge compressor already running, and interior lighting really do draw current at the same time and their watts genuinely stack. A startup surge is treated differently: only the single largest one counts, on the assumption that a second motor is unlikely to start at the exact same instant as the first. That assumption holds for most real RV use, where a fridge compressor and an air conditioner compressor rarely both kick on in the same fraction of a second, but it is an assumption rather than a guarantee. A generator sized with no margin at all against this page's numbers leaves no room for the rare moment when two things do start together, which is one more reason the headroom in a slightly larger generator class, or a soft starter on the largest load, is worth the extra cost.

Never run any generator, soft starter installed or not, inside an enclosed space. Models like the WEN 6800W Dual Fuel and the Pulsar PGD40ISCO include a carbon monoxide shutoff sensor as a safety feature, not a substitute for keeping the exhaust pointed away from windows, vents and neighboring rigs.

Generators that match this chart

Intermediate Close alternative

ERAYAK

ERAYAK 4500W Dual Fuel RV-Ready Inverter Generator

$559.00

A 4,500W dual fuel unit that covers the same scenario with slightly less headroom to spare.

Best for: Running on the propane already onboard.

Check price on Amazon

Expert More headroom

WEN

WEN 6800W Dual Fuel RV-Ready Inverter Generator

$798.00

Rated to 6,800W starting, enough margin to add a 15,000 BTU unit or more other loads without a soft starter.

Best for: A large rig or two air conditioners.

Check price on Amazon

Beginner Pair with a soft starter

Pulsar

Pulsar PGD40ISCO 4000W Inverter Generator

$450.07

At 4,000W starting, this unit needs a soft starter fitted to reliably start a 13,500 BTU air conditioner alongside much else running at once.

Best for: Occasional use where weight matters most.

Check price on Amazon

Frequently asked questions

What size generator do I need to run a 13,500 BTU RV air conditioner?: At minimum, a generator rated for at least 3,000W starting watts if nothing else is running at the same moment the compressor starts. In practice most rigs have other loads such as the converter or a fridge running too, so a 3,500W to 5,000W generator without a soft starter, or a 2,000W to 3,000W generator with one fitted, covers the common real-world scenarios shown in the tables above.
Why is my needed generator size so much bigger than the air conditioner's running watts?: Because a generator has to survive the brief startup surge, not just the steady running load. A 13,500 BTU unit runs at about 1,400W but surges to roughly 3,000W for a fraction of a second at startup, and the generator's starting watts rating, not its continuous running watts rating, is the number that has to cover that surge.
Does a soft starter really let me use a smaller generator?: Yes, often by a meaningful margin. Cutting a 13,500 BTU air conditioner's 3,000W startup surge to roughly 1,200W with a soft starter can drop the required generator class from 5,000W down to 3,000W in a scenario with 1,800W of other loads running, based on the table above. That is often one or two standard generator size classes smaller, and a soft starter typically costs less than the price difference between those classes.
Can I run two RV air conditioners off one generator?: Only if the generator's starting watts rating covers both units' running watts plus the larger of the two units' startup surge, assuming the two compressors do not start at exactly the same instant. Run your specific combination of running loads and the larger unit's surge through the generator size calculator rather than assuming a published figure covers a two-unit scenario, since none of the figures on this page assume two compressors.
What generator wattage does a 30 amp RV pedestal roughly replace?: A 30A RV shore power service is rated at 3,600VA, a published NEMA TT-30 figure. That is a useful rough comparison point, though a generator's starting watts rating and a pedestal's continuous VA rating are not measuring quite the same thing, since the pedestal has no equivalent startup surge limitation of its own the way a generator does.
Is starting watts or running watts the number on a generator's price tag and marketing?: Generator marketing usually leads with the larger starting watts figure, since it is the bigger number, while the continuous running watts rating is typically listed lower in the specifications and is meaningfully smaller. Both figures matter for different reasons: starting watts decides whether a compressor-driven load will start at all, and running watts decides what the generator can sustain once everything is already running.

Check the surge before the running load. A generator that easily covers everything running steadily can still fail on the one compressor that has to start, so run your own other-loads total and air conditioner size through the tables above before buying.