When shopping for a portable generator, the first decision is whether to buy an inverter generator or a conventional (open-frame) generator. They work differently, produce different quality power, and are suited to different uses. Here's what you need to know to choose the right one.
How They Work
Conventional Generators
A conventional generator runs an engine at a constant speed (usually 3600 RPM) to produce AC power. The engine speed doesn't change regardless of the load — it must maintain that speed to keep the frequency at 60 Hz. This is simple, proven technology that's been used for decades.
Inverter Generators
An inverter generator produces AC power, converts it to DC, then inverts it back to clean AC power. The engine speed varies with the load — it runs slower when the demand is low and speeds up when demand increases. This makes them quieter and more fuel-efficient.
Power Quality
This is the biggest difference and the most important factor for sensitive electronics.
Conventional generators produce power with some voltage and frequency fluctuation. The Total Harmonic Distortion (THD) is typically 15–25%. This is fine for power tools, lights, and appliances with motors. But it can damage or shorten the life of sensitive electronics like laptops, phones, and TVs.
Inverter generators produce clean power with less than 3% THD — similar to household power. This makes them safe for laptops, phones, medical equipment (CPAP machines), and other sensitive electronics.
Noise Level
Conventional generators are loud — typically 65–75 decibels at 23 feet. That's about the volume of a vacuum cleaner or a busy street. You can't have a conversation next to one.
Inverter generators are much quieter — typically 50–60 decibels. That's about the volume of normal conversation. Many campgrounds require inverter generators because of noise restrictions.
Fuel Efficiency
Conventional generators run at full speed regardless of load, so they consume fuel at a steady rate. A 5000-watt conventional generator might run 8–10 hours on a tank of gas regardless of whether you're using 500 watts or 4000 watts.
Inverter generators adjust engine speed to match the load. At low load, the engine slows down and sips fuel. A 2000-watt inverter generator might run 8–10 hours on a tank at 25% load but only 4 hours at full load.
Portability
Conventional generators are heavy — a 5000-watt unit can weigh 120+ pounds. They're typically mounted on wheels but aren't easy to move around.
Inverter generators are lighter and more compact. A 2000-watt inverter generator weighs 40–50 pounds and often has a carry handle. They're designed to be moved.
Parallel Operation
Most inverter generators can be paired with a second identical unit using a parallel cable to double the output. This gives you flexibility — run one for light loads, connect two for heavy loads. Conventional generators cannot be paralleled.
Cost
Conventional generators are less expensive per watt. A 5000-watt conventional generator costs $400–600.
Inverter generators are more expensive per watt. A 2000-watt inverter generator costs $400–600 — the same price but with less than half the power.
Which One Should You Buy?
Choose a Conventional Generator If:
- You need to power heavy loads (well pumps, air compressors, RV air conditioners, multiple appliances)
- You're using it for job sites or backup power where noise isn't a concern
- You need maximum watts per dollar
- You don't need to power sensitive electronics
Choose an Inverter Generator If:
- You're powering sensitive electronics (laptops, phones, CPAP, TVs)
- Noise is a concern (camping, tailgating, close neighbors)
- You want fuel efficiency for long run times
- Portability is important
- You want the option to parallel two units
The Hybrid Option
If you need both — quiet, clean power for some uses and high wattage for others — consider buying a smaller inverter generator for electronics and a larger conventional generator for heavy loads. Many RV owners use exactly this setup.
A Note on Surge Watts
Both types have a rated (running) wattage and a surge (starting) wattage. Electric motors (in air conditioners, refrigerators, pumps) need 2–3 times their running watts to start. Always size your generator for the surge load, not just the running load.
The Bottom Line
For most homeowners and recreational users, an inverter generator is the better choice — it's quieter, cleaner, and more efficient. For heavy-duty backup or job site power, a conventional generator delivers more watts per dollar. Match the generator to your actual needs, not to the biggest wattage you can find.