What size generator for 13,500 BTU RV AC?

Without soft start: 3,000W minimum, 3,500W recommended. With soft start: 2,200W inverter generators can often run it.

Can a 2,000W generator run an RV AC?

Usually not without a soft start. The startup surge (2,500W+) will trip the generator's overload. With a soft start, a 2,200W inverter unit is often sufficient.

Does altitude affect generator power?

Yes. Generators lose ~3-4% of power for every 1,000 feet of elevation. If camping at 5,000ft, you need ~15-20% more capacity.

Should I use an inverter or conventional generator?

Inverter generators provide cleaner sine-wave power, which is safer for AC compressors and control boards. They are also much quieter.

Can I run two ACs on one generator?

You typically need 5,500W+ and a 50-amp connection. With soft starts on both, a 4,500W-5,500W unit may work depending on other loads.

RV Generator Sizing for AC: Calculating Load & Startup Watts

Don't overload your generator. BTU-to-Wattage table + altitude adjustments.

🔎 30-Second Summary

Proper sizing of an RV generator for air conditioning requires attention to both startup and running wattage. A minimum generator size of 3,000W is recommended for a 13,500 BTU AC unit, considering altitude effects and using inverter generators for sensitive electronics.

Generated from this page. Always verify technical specs.

Quick Repair Toolkit

Generator sizing and load verification usually requires these tools.

Tool	Why You Need It
🔧 Best Multimeter for RV	Verify voltage under load
🔧 Best RV Generators	Compare models for your AC size
🔧 Best RV EMS Systems	Monitor voltage when running on generator

AI Summary: RV Generator Sizing for AC

The Math: Sizing must account for "Startup Surge" (2,500W–3,500W), not just "Running Watts" (1,500W–1,800W).
The Minimum: A 3,000W generator is typically the smallest reliable unit for a single 13.5k BTU AC without a soft start.
The Elevation Factor: Inverter generators lose ~3.5% of their output for every 1,000 ft of altitude above sea level.
Soft Start Impact: Installing a soft start can lower the requirement to a 2,200W inverter generator (e.g., Honda EU2200i).
Safety First: Never use a construction-grade generator (open frame) for sensitive AC control boards; inverter power is required.

The Bottom Line: Running an RV air conditioner on a generator is the most power-intensive task you will perform. If your generator is undersized, it will sag in voltage, causing the AC compressor to overheat and trip the internal thermal overload. For a standard 13,500 BTU unit, aim for 3,500 peak watts.

1. Understanding the Wattage Math (BTU vs. Watts)

Air conditioners are rated in BTUs (British Thermal Units) for cooling power, but your generator cares about Watts. While efficiency varies, the conversion math for standard RV rooftop units is consistent.

AC Unit (BTU)	Running Watts	Startup Surge (LRA)	Min. Generator
11,000 BTU	1,000–1,200W	2,000–2,400W	2,500W
13,500 BTU	1,400–1,600W	2,700–3,100W	3,000W
15,000 BTU	1,700–1,900W	3,300–3,600W	4,000W

Startup surge is the "Peak Wattage" required to get the compressor motor spinning from a dead stop. This lasts roughly 150-300 milliseconds but is enough to trip the "Overload" circuit on a generator instantly. See AC amp usage for the underlying electrical theory.

🔧 Field Insight: Many budget generators advertise a "3500" or "4000" in their name, but that is the Peak/Starting rating. Always look for the Continuous/Running rating to ensure you have enough power for long-term cooling.

2. Inverter vs. Conventional (Open Frame) Generators

Generator quality matters just as much as wattage. Inverter generators produce a "pure sine wave," which is identical to the power in your home. Conventional generators produce "dirty power" with THD (Total Harmonic Distortion) that can exceed 15%.

%%{init: {'theme':'default'}}%% graph TD A[Inverter Generator] -->|Pure Sine Wave| B[Safe for AC Boards & LCDs] C[Open Frame Generator] -->|Square/Modified Wave| D[Voltage Spikes & Noise] D -->|Heat| E[Compressor Failure] B -->|Clean Signal| F[Longer AC Lifespan]

Most modern RV ACs (Dometic, Coleman Mach) have digital control boards. "Dirty" power from an open-frame generator causes these boards to glitch or burn out. Furthermore, open-frame generators are significantly louder (75dB+) compared to inverters (52–58dB), which will get you kicked out of most campgrounds. Check best RV generators for HVAC for pure-sine recommendations.

3. The "Altitude Penalty" (Elevation Math)

Generators require oxygen to create combustion. As you climb into the mountains, the "thinner" air reduces the engine's power output. This is a linear loss that many boondockers forget until their AC won't start at 6,000 feet.

🔧 Field Insight: If you plan on high-altitude camping, you must oversize your generator. A 4,500W unit is the safest bet for mountain boondockers who need cooling.

4. The "Cheat Code": Installing a Soft Start

If you already own a 2,000W or 2,200W generator (like a Honda or Predator) and don't want to buy a 4,500W beast, a soft start kit is your best friend. By reducing the LRA surge, it allows a smaller generator to successfully ramp up the compressor without hitting its overload limit. See the step-by-step install guide for details.

5. Proper Connection and Wiring

The "weakest link" in your power chain is often the cord. Using a long, 14-gauge household extension cord will cause a **voltage drop**. When voltage drops, the compressor pulls more HEAT and more AMPS to compensate.

6. Frequently Asked Questions

Should I turn off Eco Mode?

Yes. ECO mode allows the generator to idle down when load is low. However, it cannot "rev up" fast enough when the AC compressor kicks on, causing an instant overload. Always run in "Standard" or "Rabbit" mode when using the AC.

Can I run my AC and Microwave on one generator?

Only if you have a 4,500W+ generator. A 13.5k BTU AC pulls ~1,500W and a Microwave pulls ~1,200W. Combined with your battery charger (converter), you will be right at the 3,000W limit of most medium units.

Do dual-fuel generators lose power on Propane?

Yes. Propane has less energy density than Gasoline. Expect a 10–15% drop in wattage when running on LPG. Factor this into your sizing math.

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DecisionGrid content is independently researched. We evaluate products using technical specifications, wattage math, and compatibility checks—not sponsor relationships. Affiliate links do not influence rankings. Our safety-first philosophy prioritizes voltage protection, load calculations, and real-world use cases. Content is reviewed quarterly; specs are verified and broken links fixed. We do not accept sponsored placements or paid rankings.

About the Author

Adam Hall — Founder, DecisionGrid

DecisionGrid's technical guides are written and reviewed using:

System-level electrical analysis
Real-world RV troubleshooting patterns
Manufacturer documentation review
Field-tested diagnostic workflows

Our goal: Clear, structured troubleshooting — not guesswork.

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Updated March 2026 · Reviewed for technical accuracy