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4 and a Half stars

Review of the Generac GP3500iO Open Frame Portable Inverter Generator

3500 Starting Watts, 3000 Running Watts on Gasoline

Electric Start: No

Weight: 74.3lbs

Noise: 0dB


Should You Buy It?

Generac pride themselves in having over 60 years of experience in the manufacture of generators. They were pioneers in the production of affordable power equipment for the home in the US and now sell more generators than all their competitors combined.

If you are looking for a portable inverter generator with more power than many of the other smaller inverters then yes, this would be a good choice. It isn't the cheapest out there, but it's well-made and there are very few reported problems. The lack of an optional wheel kit and an electric start may end up disqualifying it for people who have difficulty lifting something that weighs this much. But for other potential buyers it appears to live up to its reputation of being pleasantly quiet and efficient.

Key Points about the Generac GP3500iO

Plenty of 5-stars from owners
Easy to set up and get going
Fuel gauge and Hour meter
Parallel capable
Open frame so noisier
No option for a wheel kit
No electric start

Overview of the Generator


The Generac GP3500iO is an open frame inverter generator featuring new advanced PowerRush™ technology, which Generac say delivers over 50% more starting power. It's both quiet and light and is an ideal companion for camping and powering your RV essentials or tools. It's also a useful solution for keeping essential appliances on for limited periods when the electricity grid is down for whatever reason.

Controls and Features


Besides receptacles and circuit breakers, the control panel has a variety of user-friendly features. They include a recoil cord starter, a Power Dial, an Hour Meter, an Eco Mode, parallel connectors, and a grounding lug. Three LEDs provide you with information about the generator's readiness for connections (green), an overload condition (red), and low oil level (yellow). If the oil level drops below a safe point the engine stops automatically. You won't be able to get it going again until you've added more oil.

You use the Hour Meter to keep an eye on when it's necessary to carry out scheduled maintenance. Carefully following the manual's guidance on this should extend the generator's useful life.

The Eco Mode switch ensures the quietest operation, improves fuel efficiency, and reduces emissions. It's used when you only need to power small appliances, such as a TV, lights, a radio, or a video game. It should be in the Off position when connecting motor-driven equipment that turn on and off, such as an RV air conditioner, and resistive loads like a hair dryer.

There is no electric start option for this model.

For appliance connections there are 2x120v household outlets, 1x120v 30A twist lock outlet and 2xUSB port (1x1A and 1x2.1A 5v).

As the GP3500iO is EPA Certified and CARB Compliant it can be used in all 50 states.

Generac offer a 3-Year Limited Warranty for residential use, and 1-Year for commercial applications.

Detailed information for this model is contained in the Generac GP3500iO manual.

It is not equipped with a sensor to monitor levels of the dangerous carbon monoxide gas while the generator is in operation.

Power Output

Generac's GP3500iO is powered by a 212cc OHV engine producing a starting output of 3500 watts and a running output of 3000 watts. You can double this by connecting to another GP3500iO, a iQ3500E or a GP3000i in parallel, using an optional kit (76680-0). It can also be hooked up to a transfer switch in a house, either on its own or when connected in parallel with one of the generators just mentioned. It runs for up to 8 hours at a 50% load.

As it uses inverter technology, this model has the benefit of producing clean power output (of <3% THD), so you can connect sensitive electronic equipment without worrying about dangerous spikes in the current causing damage.

When choosing a portable generator, make sure you take into account where you live. This is essential because altitude and ambient temperature can significantly affect the performance and output that any generator can produce at sea level.


At 74.3lbs this is a reasonably light weight model. However, it is not designed to accommodate an optional wheel kit to help you move it around more easily.

Noise Level

Although Generac do not reveal decibel ratings for any of their generators, they say the GP3500iO is quieter than most portable power sources. Placed a reasonable distance away, this generator's noise level will probably be on a par with most other similar models.

What Most Buyers Like

For most owners this model is a big success, and they award it with 5-stars. It's well-packaged and easy to get going. Although it's not the cheapest compared to some alternatives, most would recommend it to other potential buyers. It powers a 13500 BTU RV air conditioner with ease, and some owners are pleased that it isn't too loud. One buyer thinks it should have been equipped with a 30 Amp RV plug instead of the 30LR5 Twistlock, as its absence means you have to buy a separate adapter for use with an RV. Again, have a look at some examples of available adapters.

What Some Buyers Like Less

Several prospective buyers would have liked Generac to publish decibel (dB) levels. Generac's response is: "As there is no set industry standard for dB ratings of portable generators, it's difficult to compare the models. The GP3500iO is an open frame inverter, which means it will be louder than a suitcase style generator that is fully enclosed but is still significantly quieter than a traditional style portable generator. For camping purposes, we recommend using the suitcase style inverters, like the iQ2000". Note: this model appears to be no longer available. An alternative to this may be the Generac GP2200i.

It's not a very heavy generator, but buyers regret Generac's confirmation that there is no wheel kit option for this model.

AC Rated Output Running Watts3000
AC Maximum Output Starting Watts3500
Rated AC Voltage120 VAC
Rated AC Frequency 60 Hz
Rated 120 VAC Amperage 25
Engine Displacement 212cc
Engine TypeOHV
Engine RPM OilVariable
Recommended Oil 10W-30 / SAE 30
Capacity qt (L) 0.6 (0.6)
Lubrication MethodSplash
Parallel CapableYes (Kit 7668-0)
Total Harmonic Distortion (THD)<3%
Choke LocationIn PowerDial
Fuel Shut OffOn Fuel Tank
Starting MethodRecoil Pull Start
Low Oil ShutdownYes
Floating Neutral Yes
Neutral Bonded to GroundNo
Start Switch Type PowerDial
Start Switch Location On Control Panel
Outlets (120V)1x20A 5-20R Duplex,
1x30A L5-30R Twist Lock
Fuel Tank Capacity gal (L) 2.37 (9)
Run Time at 50% (Hours) 8
Run Time at 25% (Hours) 11
Warranty- Residential3 Year Limited
Warranty- Commercial1 Year Limited
IncludedEngine oil, oil funnel
Tool Kit
Owner manual
Length in (mm) 19.3 (490)
Width in (mm) 16.9 (430)
Height in (mm)16.4 (417)
Carton Length in (mm) 19.8 (502)
Carton Width in (mm) 17.5 (455)
Carton Height in (mm) 18.1 (460)
Unit Weight lbs (kg) 74.3 (33.7)
Shipping Weight lbs (kg)80.7 (36.6)