When EG4 launched the FlexBOSS 21 last year, it shook up the home power market by offering serious performance at a surprisingly low price. All of that performance was also wrapped in a plug-and-play package that had a solid weather rating and was really easy to install.
But what if you don’t need all of the power and features you get with the EG4 FlexBOSS 21? That’s exactly where the EG4 FlexBOSS 18 comes in.
It’s a bit smaller, more affordable, and geared more towards basic backup for residential homes, cabins, and smaller off-grid setups. But with specs and pricing so similar to the FlexBOSS 21, does the FlexBOSS 18 bring anything new to the table—or is it just a somewhat cheaper version of basically the same thing?
Let’s find out.
If you’re familiar with the FlexBOSS 21, you’ll immediately notice the design of the 18 is almost identical—but there are a few notable differences under the hood. However, before we get into what we like and dislike about this unit, here’s a quick breakdown of what the EG4 FlexBOSS 18 offers:
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Like we did with the 21, we put the FlexBOSS 18 through some serious testing. Overall, it really impressed us. It worked exactly like we expected it to, and even surprised us in a few categories by overperforming its rated specs. Here’s just a few of the areas where we think it really shined:
Despite its slightly smaller footprint and lower inverter rating compared to the FlexBOSS 21, the FlexBOSS18 surprised us during testing. It ran full 10,000W loads comfortably and even managed to surge-start a 10kW air compressor—all while running at full capacity. That’s a level of surge performance you rarely see in a unit with these specs.
By removing the 200A pass-through seen in the FlexBOSS 21, EG4 made this unit more approachable and affordable, especially for off-grid users and homeowners with smaller setups.
If you do want the 200A capability, it pairs perfectly with the GridBOSS, which adds advanced load control and makes installation cleaner and easier. (We’ve reviewed the EG4 GridBOSS MID too, and it’s a fantastic companion to this system).
Like the FlexBOSS 21, it also has a lot of nice weather-proofing details. This includes the snap-lock doors that would prevent them from swinging open during high winds, as well as the sealing around all of the venting and the main door, which will help keep moisture and debris out.
One of the big strengths of the FlexBOSS line is how easy these units are to install. Like we found with the 21, the wiring terminals are straightforward and accessible, and you get knockouts on the back and bottom to hide your cables cleanly.
The Wi-Fi dongle comes standard, and if you prefer a screen, the optional $100 display is well-worth the money. In fact, it’s actually the same high-quality display screen you get on the EG4 18KPV Hybrid Inverter. If you’ve seen our review of the 18KPV, you’ll know that the display screen is one of our favorites on any piece of solar equipment—it’s bright, clear, and super easy to use. Again, for 100 bucks, it's a bargain, but it's nice they don't include it for those who would like to keep things as budget-friendly as possible.
This may be the quietest inverter EG4 has ever made. Both the EG4 18KPV and the FlexBOSS 21 are louder when running any sort of load than the FlexBOSS 18 is at full capacity. So, the fan design in this unit seems even more efficient that what they used in the 21, staying quiet even when we were pushing it with full 10,000W loads!
For those planning to install this unit in their home, it's not going to annoy you at all, even when you're pushing it hard.
With 18kW of solar input, this is a serious off-grid contender. For comparison, some inverters in this price range cap out at half that. Pair this with a large enough solar panel array, and your batteries will stay topped off even with heavy daily use.
While we were certainly impressed with this unit, we also had a few minor gripes:
While we were impressed by the surge-start capabilities, the surge duration isn’t great. If you go even slightly over the 10kW continuous rating—say, 10.1kW—while off-grid, it will shut down in 10 to 15 seconds. Other inverters allow longer surges to give users time to react and correct the issue, which would be nice here.
UL certification in California requires a rapid shutdown feature, and the FlexBOSS 18 does include one. However, shutdown seems to take 15 to 20 seconds, even with the added external button that’s supposed to speed it up. That’s not what we’d call “rapid.” It works, we're happy it has it, and the feature definitely meets code, but there’s clearly room for improvement here. It would have been nice if EG4 went further than the minimum requirements for UL certification.
Our unit showed up with a dent and a cracked corner, which we assume would compromise the unit’s NEMA 4X weatherproof rating.
That’s not directly EG4’s fault—FedEx likely tossed it around like they do with all of our packages—but the packaging itself was a little lighter than what we’ve seen from other EG4 products. Basically, it was just a standard cardboard box with some basic Styrofoam padding in the corners. A sturdier box or even a protective crate would have prevented that avoidable damage, no matter how badly FedEx slapped it around.
Fortunately, EG4 makes the front panel easy to replace, and we’re confident their support team would have sent us a replacement without issue. Still, stronger packaging would have avoided the problem entirely.
We really can't recommend this unit highly enough. So, the only question is choosing between the FlexBOSS 21 and the FlexBOSS 18. If you're stuck deciding between the two, here’s a simple breakdown:
The FlexBOSS 18 does almost everything the 21 does, just on a slightly smaller scale, and it’s available for roughly $500 less. Plus, it’s lighter and even quieter. Like the FlexBOSS 21, it also pairs flawlessly with the EG4 GridBOSS, so it’s also just as suitable for hybrid setups.
Overall, we’re very impressed with what EG4 has delivered here. It’s smartly designed, performs reliably, and we think it will be a welcome option for a lot of consumers.
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