What is the difference between running watts and startup watts for an RV air conditioner?

Running watts is the steady draw once the compressor motor is up to speed, typically 1,150W to 1,700W across common RV rooftop sizes. Startup watts is the brief, much larger surge the compressor pulls at the instant it starts, roughly double to more than double the running figure. Any power source has to survive the startup surge even though it only lasts a fraction of a second, or the compressor never gets moving.

How much does a soft starter reduce air conditioner startup watts?

The commonly cited figure for the class of device is roughly a 60 percent reduction, which this site applies as a 0.4 multiplier convention on the startup watts figure. A 13,500 BTU unit's 3,000W startup surge falls to about 1,200W with a soft starter fitted. Individual soft starter models and individual compressors can vary from that figure, so treat it as a planning convention rather than a guaranteed spec.

Can a 2,000W generator run a 13,500 BTU RV air conditioner?

Not without a soft starter. The unit's roughly 3,000W startup surge exceeds a 2,000W generator's rated starting watts, so the compressor will not start and the generator may stall or trip a breaker trying. With a soft starter cutting the surge to roughly 1,200W, a 2,000W generator has enough headroom to start the compressor, provided nothing else large is running on the generator at the same moment.

Do all 13,500 BTU RV air conditioners draw exactly the same startup watts?

No. The figures on this page are typical published values for the BTU class, used consistently across this site's calculators, but individual compressors and manufacturers vary. Check the data plate on your own unit for its actual rated running and locked rotor amperage, and treat this chart as a planning reference rather than a substitute for that label.

Does a soft starter change the running watts of an air conditioner?

No. A soft starter only limits the current spike at the moment the compressor motor starts. Once the compressor is running normally, the steady running watts figure is unchanged, since a soft starter does nothing after the brief startup window closes. Sizing a generator or inverter for continuous output still has to use the unadjusted running watts figure.

Does a 15,000 BTU unit need a proportionally bigger generator than a 13,500 BTU unit?

Somewhat, but not by a huge margin. A 15,000 BTU unit's published startup surge of about 3,500W is roughly 17 percent higher than the 13,500 BTU unit's 3,000W, enough to push a borderline 3,000W generator from a Yes to a No without a soft starter fitted, as shown in the table above. With a soft starter both units fall well under a 2,000W generator's rating.

Are these figures the same whether the unit is ducted or a low-profile rooftop model?

This page groups units by BTU rating rather than by ducted versus low-profile construction, since the compressor doing the cooling work, not the cabinet shape around it, is what draws the running and startup watts. Two 13,500 BTU units of different physical styles from different manufacturers can still vary somewhat from these typical class figures, which is exactly why checking the specific unit's own data plate remains the final word over any published chart.

Reference

RV Air Conditioner Running and Startup Watts Chart

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

Quick answer

A 13,500 BTU RV air conditioner draws roughly 1,400W running and about 3,000W to start. A soft starter cuts that startup surge to roughly 1,200W, a convention of about a 60 percent reduction, which is what lets a 2,000W generator start a unit it otherwise cannot. Generators and inverters are sized against the startup number, never the running number, because the compressor's locked rotor current is always the bigger load.

An RV rooftop air conditioner's compressor draws far more current for a fraction of a second at startup than it does once running, a behavior common to any motor-driven compressor. That startup surge, not the running watts printed on the unit's label, is the number that decides whether a generator, inverter or shore pedestal can actually start it. The figures below are typical published values for each BTU class; always check the data plate on your own unit, since manufacturers vary.

A soft starter is an add-on module wired into the compressor circuit that limits inrush current electronically, and it typically cuts the startup surge by more than half. That reduction is a commonly cited convention for the class of device rather than a single certified number that applies to every soft starter and every compressor combination, but it is large enough to change which generator size actually works.

Running and startup watts by BTU rating

These are the published figures this site's air conditioner startup calculator and generator size calculator both use. The soft starter columns apply the site's 0.4 multiplier convention, a roughly 60 percent cut to the startup figure only; running watts are unaffected.

RV rooftop air conditioner power draw, without and with a soft starter
BTU rating	Running watts	Startup watts, no soft starter	Startup watts, with soft starter
11,000 BTU	1,150W	2,400W	960W
13,500 BTU	1,400W	3,000W	1,200W
15,000 BTU	1,700W	3,500W	1,400W

Published standard Source: Typical published figures for the equipment class, as used by this site's air conditioner startup load calculator. Running and startup watts with no soft starter are standard published figures for the class; the soft starter reduction is a convention, roughly a 60 percent cut, and installed soft starters vary by model.

Can a given generator size start each unit?

Reading this table: a No means the unit's startup surge exceeds that generator's rated starting watts and it will not start the compressor. A soft starter moves several No results to Yes without a larger generator.

Generator starting watts against each air conditioner's startup surge
Generator	11,000 BTU, no soft start	11,000 BTU, soft starter	13,500 BTU, no soft start	13,500 BTU, soft starter	15,000 BTU, no soft start	15,000 BTU, soft starter
2,000W	No	Yes	No	Yes	No	Yes
2,200W	No	Yes	No	Yes	No	Yes
3,000W	Yes	Yes	Yes	Yes	No	Yes
3,500W	Yes	Yes	Yes	Yes	Yes	Yes
4,000W	Yes	Yes	Yes	Yes	Yes	Yes
4,500W	Yes	Yes	Yes	Yes	Yes	Yes
5,000W	Yes	Yes	Yes	Yes	Yes	Yes

Published standard Source: Startup watts from the table above compared directly against each generator's published starting watts rating. This compares surge only. Running watts for other loads on the same generator still have to be added on top; use the generator size calculator for a full scenario.

DC current these units pull if run through an inverter

Running an RV air conditioner off an inverter instead of a generator or pedestal is possible for some units, and the steady running watts, not the startup surge, decide the DC current pulled from the battery bank once the compressor is up to speed. This uses the 0.85 inverter efficiency convention.

DC current from running watts, by air conditioner size, 12V and 24V
BTU rating	Running watts	DC amps at 12V	DC amps at 24V
11,000 BTU	1,150W	112.7A	56.4A
13,500 BTU	1,400W	137.3A	68.6A
15,000 BTU	1,700W	166.7A	83.3A

Convention Source: Running watts / 0.85 inverter efficiency convention / system volts. This is the steady draw only. The inverter's own surge rating still has to clear the startup watts figure in the first table on this page, which is a much larger, momentary number.

How these figures feed into inverter and generator sizing

The running and startup watts on this page are not an isolated reference; they are the same inputs this site's generator size calculator and inverter sizing calculator use directly. A generator has to cover the startup surge plus whatever else is running at that moment, which is why the generator sizing chart adds a second load on top of these air conditioner figures rather than treating the air conditioner in isolation. An inverter faces the same test in reverse: its continuous rating covers the running watts with headroom, but its surge rating has to clear the startup figure on this page, and not every inverter's published surge rating is large enough to do that even when its continuous rating looks adequate on paper. Checking both numbers against both figures, not just the inverter or generator's headline wattage, is what actually predicts whether a given air conditioner starts.

A soft starter reduces electrical inrush, not the mechanical cooling load. It does not make a marginal generator into a permanently adequate power source for every condition, and it does not replace checking your own unit's data plate for its actual rated locked rotor amps, which can differ from these typical class figures.

Soft starters that produce these numbers

Intermediate Alternative kit

Spartan Power

Spartan Power SpartanStart Soft Start Kit

$189.00

A second soft start option using the same current-limiting approach, for owners comparing installation styles.

Best for: A standard rooftop unit up to 20,000 BTU.

Check price on Amazon

Expert Plug and play

SoftStartRV By NetworkRV

SoftStartUp Plug and Play RV A/C Soft Start

$595.00

Fits inline at the air conditioner's power cord rather than requiring the unit to be opened, for a simpler retrofit.

Best for: Anyone unwilling to open a rooftop air conditioner.

Check price on Amazon

Frequently asked questions

What is the difference between running watts and startup watts for an RV air conditioner?: Running watts is the steady draw once the compressor motor is up to speed, typically 1,150W to 1,700W across common RV rooftop sizes. Startup watts is the brief, much larger surge the compressor pulls at the instant it starts, roughly double to more than double the running figure. Any power source has to survive the startup surge even though it only lasts a fraction of a second, or the compressor never gets moving.
How much does a soft starter reduce air conditioner startup watts?: The commonly cited figure for the class of device is roughly a 60 percent reduction, which this site applies as a 0.4 multiplier convention on the startup watts figure. A 13,500 BTU unit's 3,000W startup surge falls to about 1,200W with a soft starter fitted. Individual soft starter models and individual compressors can vary from that figure, so treat it as a planning convention rather than a guaranteed spec.
Can a 2,000W generator run a 13,500 BTU RV air conditioner?: Not without a soft starter. The unit's roughly 3,000W startup surge exceeds a 2,000W generator's rated starting watts, so the compressor will not start and the generator may stall or trip a breaker trying. With a soft starter cutting the surge to roughly 1,200W, a 2,000W generator has enough headroom to start the compressor, provided nothing else large is running on the generator at the same moment.
Do all 13,500 BTU RV air conditioners draw exactly the same startup watts?: No. The figures on this page are typical published values for the BTU class, used consistently across this site's calculators, but individual compressors and manufacturers vary. Check the data plate on your own unit for its actual rated running and locked rotor amperage, and treat this chart as a planning reference rather than a substitute for that label.
Does a soft starter change the running watts of an air conditioner?: No. A soft starter only limits the current spike at the moment the compressor motor starts. Once the compressor is running normally, the steady running watts figure is unchanged, since a soft starter does nothing after the brief startup window closes. Sizing a generator or inverter for continuous output still has to use the unadjusted running watts figure.
Does a 15,000 BTU unit need a proportionally bigger generator than a 13,500 BTU unit?: Somewhat, but not by a huge margin. A 15,000 BTU unit's published startup surge of about 3,500W is roughly 17 percent higher than the 13,500 BTU unit's 3,000W, enough to push a borderline 3,000W generator from a Yes to a No without a soft starter fitted, as shown in the table above. With a soft starter both units fall well under a 2,000W generator's rating.
Are these figures the same whether the unit is ducted or a low-profile rooftop model?: This page groups units by BTU rating rather than by ducted versus low-profile construction, since the compressor doing the cooling work, not the cabinet shape around it, is what draws the running and startup watts. Two 13,500 BTU units of different physical styles from different manufacturers can still vary somewhat from these typical class figures, which is exactly why checking the specific unit's own data plate remains the final word over any published chart.

Size against the startup surge, not the number on the unit's spec sheet you notice first. Run your own generator or inverter capacity against the tables above, and check whether a soft starter changes a No into a Yes before buying a bigger power source.