Generac GP18000EFI Portable Generator – Pro Tool Reviews

Round Out Hurricane Season with Generac’s Most Powerful Portable Generator Yet

Portable generators provide backup power at home, at work, and away. Whether you’re shopping for a unit to prepare for hurricane season, or you’re looking for something to make camping more comfortable, Generac is a name that comes up time and time again. The Generac GP18000EFI portable generator ups the ante with the brand’s most powerful portable unit to date. I wanted to take a close look at what it has to offer so I can help you see if it’s the right solution for running your home or jobsite.

Note: Looking for a generator for the home, jobsite, or other application? Check out our picks for the best generator to see which ones we recommend!

Generac GP18000EFI Portable Generator Features

The Generac GP18000EFI portable generator is the brand’s highest-wattage unit available as of the beginning of 2024. Equipped with an 816cc EFI engine, this powerhouse generator delivers up to 9 continuous hours of runtime at 50% load. I don’t know about you, but that’s a good amount of runtime during a hurricane, and I likely won’t need to average more than 9,000 continuous Watts in an emergency…though I may want to. It certainly ensures I can go through the night without having to get up and refill the tank!

Generac GP18000EFI 50A connection

With a running wattage of 18,000W, this Generac generator provides the capacity to provide whole-home backup power when paired with a HomeLink manual transfer switch or when wired directly through a breaker interlock. I opted for the latter method. It lets me operate any of the circuits in my home while still maintaining NEC compliance

There are a total of 7 power ports, letting you power a variety of electronics and appliances around your home. Plus, Generac’s TruePower technology allows you to safely power sensitive electronics and tools.

Generac GP18000EFI generator reviewGenerac GP18000EFI generator review

Included Power Connection Ports

  • 30A @ 120V
  • 30A @ 120/240V
  • 4x 20A @ 120V (two duplex outlets)
  • 50A @ 240V

For safety features, the Generac GP18000EFI generator also includes COsense technology. This all-but-mandated system alerts you when it detects high carbon monoxide levels. That can save lives. Though you might think it’s obvious never to operate a generator in an enclosed space, sadly, people die every year from this very thing.

A low-oil pressure shutdown also safeguards the engine from damage should the oil run low for any reason.

Key Features

  • 7 power ports (30A/120V, 30A/240V, 4x20A/120V, 50A/240V)
  • TruePower technology
  • COsense technology
  • Low oil pressure shutdown
  • Compatible with Homelink Manual Transfer Switch
  • Heavy-duty never-flat wheels
  • Folding handles
  • Hardened steel tube cradle
  • Large-capacity fuel tank (14.2 gallons)
  • Hour meter tracks maintenance intervals


  • Model: Generac GP18000EFI (8917)
  • Watts (starting/running): 22,500/18,000
  • Horsepower (hp): 24.1
  • Engine displacement (cc): 816
  • Dimensions (LxWxH): 59 x 31 x 37 inches
  • Weight: 439 pounds

Generac GP18000EFI Portable Generator Design

The generator arrived on a pallet and required some minimal assembly. I had to install the wheels as well as the front bracing and rubber feet.

flat free wheelsflat free wheels

The generator weighs a hefty 439 pounds (dry), but you might not know it. It features heavy-duty never-flat wheels that let it roll easily across our shop floor and over the threshold. It does have trouble over grass, however. Generac would be wise to issue future models with larger pneumatic tires to better handle jobsites and uneven terrain.

The handles fold down flat for compact storage. They also provided plenty of leverage when I moved the unit from the shop to each 50A inlet port.

Generac GForce EFI 816cc engineGenerac GForce EFI 816cc engine

Generac gives you a 14.2-gallon steel fuel tank in the GP18000EFI for long runtimes. An integrated fuel gauge and digital hour meter let you keep an eye on your runtimes and fuel levels.

fuel level gas capfuel level gas cap

Finally, this unit is surrounded by a hardened 1 1/4-inch steel tube “cradle” that provides additional durability and protection. It also gives you something nice to anchor a chain to for security.

Using the Generac 8917 to Power Our Shop

After moving to Florida in 1992 and having stayed through a fair amount of hurricanes, it should come as no surprise that I added a transfer switch to my shop. What may come as a surprise is that it “only” took me 6 years to do it!

As I mentioned earlier, I opted for a simple breaker interlock for a couple of reasons. First, I wanted access to all of the circuits in the shop. Second, I did indeed add a breaker interlock to my 2600-square-foot Pro Tool Reviews shop (it has its own power and panel). I skipped the transfer switch as it only allows for a handful of breakers/circuits. Instead, I wired both this and my house panels with interlocks and breakers for a couple of hundred dollars each.

electrical panel interlock breakerelectrical panel interlock breaker

Our first test involved turning off the individual and main breakers in the shop. Following this I started up the Generac GP18000EFI and let it run for a few minutes. I then engaged the interlock and connected the 50A/240V 4-prong outlet of the generator to the 50A input port next to my shop panel.

generator 50A inlet boxgenerator 50A inlet box

With this configuration, I was able to operate the entire shop, including its 2.5-ton AC unit, all of the lights (office and shop), plus our 5 computers and our Gaggia Espresso machine.

Not satisfied, I then turned on both mini splits that cool the shop space. The Generac GP18000EFI handled it all. As a last test, I ran some hot water which activated the tankless heater wired into its own 60A circuit. The generator dipped in speed as it adjusted, but everything stayed up and running. About the only thing I didn’t operate was our 240V air compressor and a table saw!

Using the Generac 8917 to Power a Large Home

After the success with the shop, I wheeled the Generac GP18000EFI over to my house. I connected it to the 50A port which ties into the 200A panel. Following the same procedure, I turned off the breakers and the main, started and warmed up the generator, and engaged the interlocked breaker.

home 200A panel breaker interlockhome 200A panel breaker interlock

This time around, I engaged all of the primary 20A breakers in sequence to see if we could free up the entire house for lighting and power. Next, we had to decide what we could activate in terms of larger circuits. We did not turn on the breakers for the dedicated AC in my home theater room, the pool pump or heater, our microwave, or the Bosch induction range.

That left us with a couple of major tests. Could we activate our hybrid hot water heater? More importantly, could we run the 5-ton AC unit for the home? That may sound silly, but when hurricanes hit in Florida, the temperature doesn’t suddenly drop and make the home comfortable as you’re trapped inside without power. Having AC helps a ton… or 5-tons.

Generac GP18000EFI 50A connectionGenerac GP18000EFI 50A connection

In short—yes. I was able to operate the 5-ton AC unit, the water heater, lights, two refrigerators, and our coffee machine (oh so important!). It would probably handle more, but I wasn’t trying to max it out so much as to simulate what I wanted to do in the event of a power outage during the next hurricane.

Final Analysis—What Can It Run?

Lots! The Generac GP18000EFI truly serves as a capable portable whole-home generator. It not only allowed us to run all of the lights, outlets, and critical appliances in our home and shop, but it also did much more. It ran our 5-ton AC unit AND our hybrid hot water heater. That’s impressive as it means the generator handles the inrush currents associated with a large AC unit as well as the needs of a hybrid hot water heater. The key is not activating the circuits all at once.

In our shop it allows our company to stay up and running, comfortably, for 8 hours or more on a single tank of gas. This is due to the fact that we aren’t operating the generator at over 50% capacity (on average) with that facility. Unless we maximize and run all AC units and the tankless hot water heater to take a shower, we stay at a moderate level of power consumption.

In our opinion, you can’t buy a more powerful or capable generator to operate your large home or your home office. If you want instant automatic power when the power lines fail, then perhaps a Generac Guardian series 26kW home standby generator with a whole home switch makes more sense. If, however, you want to control costs and don’t require that level of sophistication, the GP18000EFI gets you a portable solution that works incredibly well.

Generac GP18000EFI Price

This generator retails for $4,399 and carries a 2-year limited parts & labor warranty plus an additional year parts-only warranty. You can find it wherever Generac products are sold. Generac backs your purchase with a 3-year residential/2-year commercial warranty. Check out the Generac website if you want more information.

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