Running an RV HVAC system on a generator involves more than simply matching BTU ratings. Factors such as startup surge, electrical service, compressor design, and total appliance load can all affect whether a system performs reliably. 

Understanding a few basic electrical concepts can make it easier to choose a compatible generator and avoid common frustrations. 

One of the first things to understand is whether your RV uses 30 amp or 50 amp service. This can often be found near the RV power inlet, on electrical labels near the hookup connection, or in the owner's manual. 

Quick Comparison

Running wattage does not tell the full story. RV HVAC systems often require significantly more power during startup than during normal operation. 

Running watts: The power required during steady operation after the system is already running

Starting watts / surge watts: The brief but much higher power draw required to start the compressor. This startup surge is often what causes tripped breakers or struggling generators. 

Fixed Speed Compressors

Traditional fixed speed systems typically start up at full power every time cooling is needed. This repeated on/off cycling can create larger startup surges that may overwhelm generators. 

Some fixed speed systems can briefly draw 2-3 times their running wattage during startup. 

Variable-Speed / Inverter Style Systems

Variable-speed systems gradually ramp output up or down based on cooling demand rather than repeatedly starting at full power. 

Benefits

• Reduced startup intensity
• Improved generator compatibility
• Smoother operation
• Easier on smaller inverter generators

Because startup demand is often lower, generator-powered operation may feel more manageable compared to fixed speed systems. 

Power requirements vary by system and operating conditions, but the following is a general example: 

Many 13.5K BTU - 15K BTU systems require approximately: 

• 1,200 - 1,800 running watts
• 1,500 - 3,000+ startup watts

Actual requirements are affected by compressor design, outdoor temperature, efficiency, and additional connected loads. 

In some situations, reducing other electrical loads may help. 

Examples include: 

• Turning off microwaves
• Turning off electric water heaters
• Avoiding running other high-draw appliances simultaneously
• Allowing the fan to start before heavy cooling demand increases
  • Important Note: Installing non-approved electrical devices or operating HVAC systems outside of manufacturer guidelines or power requirements may void warranties, damage components, or create fire risks. Although alternative methods may be widely used or suggested, it is always best to follow manufacturer recommendations.

Choosing the right generator requires considering the total electrical load inside the RV, not just the air conditioner alone. 

Other appliances to keep in mind are: 

• Refrigerators
• Battery chargers/converters
• Microwaves
• Electric water heaters
• TVs and other electronics
• Small appliances and outlets

1. Identify AC Running and Startup Wattage

Check product documentation whenever possible. 

2. Add Other Essential Loads

Consider which appliances may run at the same time as the AC. 

3. Account for Peak Demand

Startup surge and simultaneous appliance usage need to be accounted for.

4. Add a Safety Buffer

Leaving additional capacity can improve reliability and reduce strain. A general recommendation is to maintain approximately 20% extra capacity beyond estimated demand when possible. 

Altitude

• Higher elevations reduce engine output due to thinner air

Extreme Heat

• Hot weather increases cooling demand and may reduce generator efficiency

Generator Maintenance

• Dirty filters, old oil, poor fuel quality, or clogged fuel systems can reduce performance and create unstable voltage conditions

RV Insulation & Heat Load

• Poor insulation, large windows, direct sunlight, and frequently opening doors can increase cooling demand significantly

A few simple habits may improve cooling performance while reducing generator strain: 

• Pre-cool the RV before peak outdoor temperatures
• Keep doors and windows closed as much as possible
• Use shade, awnings, or reflective window coverings 
• Avoid setting the thermostat temperature extremely low
• When possible, reduce simultaneous appliance usage during peak cooling demand 

Systems with variable-speed compressors or energy saving (eco) modes may also help maintain comfort with lower generator load and reduced noise. 

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

Sometimes. It depends on startup surge, compressor design, outdoor temperatures, and other appliances that operate simultaneously. 

What is the difference between running watts and starting watts?

Running watts describe the amount of power required by the AC when operating steadily after starting up. Starting watts describe the brief surge of power drawn when the rooftop units initially kicks on. This is more applicable to traditional fixed speed systems, as the startup surge occurs every time the AC cycles on. 

Do variable speed air conditioners require less power?

Variable speed units have a significantly reduced startup surge by gradually ramping up speeds rather than starting up suddenly at full power. This is much easier for a generator to handle compared to traditional fixed speed systems. 

Although startup surge is vastly reduced, the running watts are not always dramatically lower than traditional units. However, when assessing generator sizing, startup surge has a much greater effect than the running watts. 

Does higher elevation affect my generator?

Yes. Generator output decreases at higher elevations due to thinner air, which can reduce available power. 

Why does my generator trip when my AC starts?

Potential causes: 

• Startup surge
• Other appliances running at the same time 
• An undersized generator 
• A dirty air filter causing higher compressor load 
• High outdoor temperatures 

Do I need a soft start to run my RV AC on a generator?

A soft start device can make it easier for a generator to handle a fixed speed RV AC. However, it is not required if the generator is of an adequate size to handle the startup surge. Some rooftop units are already designed with soft start operation, while others may be compatible with add-on devices that enable soft start functionality. 

Variable speed units do not require soft starts. They are designed to gradually ramp compressor speeds up and back down, which means there is no large startup surge. 

Does hot weather affect generator performance?

Hotter outdoor temperatures mean increased cooling demand. This means that your system is going to work harder to maintain the set temperature inside your RV. The result is longer compressor run times and more power draw. High heat can also reduce the efficiency of generators. 

Can I run two RV air conditioners on 30A service?

The short answer: usually not. It may be possible with load management (soft start, variable speed units, reducing the amount of appliances that run simultaneously, etc), but isn't advisable. If 30A service is all that is available, you may only be able to run one unit at a time. 

Should I buy a bigger generator than I think I need? 

This is definitely the safest option. A generator with a substantial power buffer leaves room for future upgrades, adding additional appliances, and reduces the strain placed on the generator. You are much more likely to regret buying an undersized generator as opposed to one that is oversized. 

RV HVAC power requirements can vary significantly depending on compressor design, climate conditions, and overall electrical demand throughout the RV. Understanding concepts such as startup surge, electrical service, and total appliance load can help make generator selection much easier and reduce frustration when operating your RV HVAC system off grid or on limited power sources.