Orbek 18kW Tankless Water Heater Electric, ORBEK Instant On Demand Hot Water Heater 240V, Up to 4.17 GPM, Supply for 2-3 Fixtures Simultaneously, within 1℉ Stable Temp, ETL Certified, Indoor Installation

Why I switched and what I found

I replaced a tired 40-gallon tank with the Orbek 18kW tankless in a mid-size home that sees a predictable mix of morning showers, kitchen cleanup, and laundry. I wanted the usual tankless benefits—space back in the utility room, no standby losses, and steady temperature at the tap—without the complexity of a gas install. After several weeks of everyday use, this compact electric unit has lived up to most of its promises, with a few caveats any homeowner should consider before making the jump.

Installation: straightforward if you plan ahead

Physically, the Orbek 18kW tankless is refreshingly compact at 17 x 13 x 3.9 inches. It mounts easily on a wall and uses standard 3/4" NPT connections. I plumbed it with PEX and added isolation/service valves so I can flush the heat exchanger periodically—something I recommend for anyone in a hard-water area.

The electrical side is where most of the homework lives. This unit needs two separate 240V/40A two‑pole breakers and two runs of 8 AWG conductors. That’s a meaningful load; in many homes, you’ll want a 200A service to accommodate it alongside other large appliances. If you’re not fully comfortable with residential electrical work or your panel is already crowded, involve a licensed electrician and pull the appropriate permits. Once wired, initial commissioning was simple: open the valves to purge air, power up, set the target temperature, and you’re done.

One nuance worth calling out: the heater warms water in a few seconds, but “instant hot water” at the faucet still depends on how far that faucet is from the unit. You’re eliminating standby heat loss, not the time it takes water to travel through the pipe.

Performance and realistic flow expectations

For an electric tankless, performance is all about inlet temperature and flow. The Orbek 18kW can output up to 4.17 GPM, but that top number assumes a small temperature rise. Here’s what my testing and the math agree on:

• An 18kW heater provides about 61,400 BTU/hr. The temperature rise (°F) is roughly 122.8 divided by the GPM.
  
• At 2.0 GPM, you can expect roughly a 60°F rise. If your incoming water is 55°F, you’ll be around 115°F at the setpoint—plenty for a shower.
  
• At 3.0 GPM, the rise drops to roughly 41°F. With 55°F inlet, you’re near 96°F—borderline for some.
  
• At 4.0+ GPM, you’re looking at a ~30°F rise; that’s only workable in warm-climate summers or for lukewarm uses.

In my moderate-climate setup (inlet water typically 58–62°F), the unit comfortably ran a 1.8 GPM shower while someone used a bathroom sink. A second shower at the same time was doable with low‑flow heads and realistic temperature settings, but adding a third heavy draw (like a washing machine on hot) pushed it. Flow-limiting kicks in to maintain temperature, which is the right behavior, but it’s a reminder that sizing matters.

Where the Orbek shines is temperature stability. I set it to 120°F and saw it hold steady—no hunting, no sudden swings as other fixtures opened. The control system reacts quickly to flow changes, and the showers felt consistent from start to finish. The output is essentially silent in operation, aside from a faint click on power-up and the whoosh of water through the unit.

Controls and everyday usability

The interface is intentionally simple: a clear LED display with up/down temperature control from 86°F to 140°F. I landed on 120°F for most uses and left it there. The screen is easy to read, the buttons feel positive, and the unit remembers your setpoint. If you have young kids or prefer a scald margin, keep it 120°F or lower and rely on thermostatic shower valves for added safety.

Efficiency and operating costs

Removing standby losses is the main win. You’re not spending energy keeping 40 gallons hot 24/7; you’re only heating what you use. The claimed savings depend heavily on your hot water habits. Households that spread smaller draws throughout the day, or leave for long stretches, tend to see the greatest advantage. Heavy, simultaneous hot water use will still drive high instantaneous power draw (up to the unit’s 18kW), which is expected. For my usage pattern—morning showers, sporadic kitchen use, and a couple of laundry cycles a week—the net consumption compared favorably to my old tank, and the utility room heat spillover dropped to near zero.

Build quality and safety

Fit and finish are tidy, and the internal layout is service-friendly. The unit is ETL certified and includes protection for over‑temperature, dry heat, and leakage faults. The “water‑electricity separation” design is a nice touch; while I can’t verify long‑term scaling reduction yet, the water path and electronics are clearly partitioned. Lightning protection is cited; I still recommend whole‑home surge protection as a best practice for any modern household panel.

Maintenance

Like all tankless heaters, the Orbek will benefit from periodic descaling. Plan on annual flushes with a pump and vinegar or a manufacturer-approved solution if your water is hard; lighter schedules may be fine on softened water. There’s an inlet screen to keep debris out of the heat exchanger—give it a check every few months. If you’re in a very hard water region, consider a softener or at least a sediment filter upstream.

What I liked

• Compact footprint frees real space in the utility area.
  
• Temperature stability is excellent—showers stayed steady even with other fixtures opening.
  
• Simple, readable LED interface with precise setpoint control.
  
• Quiet operation; no burner noise, no venting requirements.
  
• Sensible safety package and ETL certification.

What could be better

• Electrical demands are significant: two 40A double‑pole breakers and 8 AWG runs. Not every panel is ready for this.
  
• “Up to 4.17 GPM” is realistic only with warm inlet water or lower output temperatures; colder climates should plan on 1–2 simultaneous low‑flow fixtures.
  
• No included service valve kit—budget for isolation valves and flush ports as part of the install.
  
• Indoor-only design, so placement is constrained in some layouts.

Who it’s for

• Homes in moderate to warm climates, or any home using low‑flow fixtures, that want reliable, stable hot water without a storage tank.
  
• Households running one shower plus a light secondary draw, or two low‑flow showers, at the same time.
  
• Owners who value compact installs and low standby losses, and who either have panel capacity or plan to upgrade.

Who should consider a different size or type

• Cold-climate households expecting multiple simultaneous high‑flow showers, a tub fill, and laundry on hot—all at once—will push an 18kW electric beyond its comfort zone. Consider a larger electric unit (with even higher electrical requirements) or a high‑capacity gas tankless.
  
• Homes with limited electrical service or no appetite for panel upgrades.

Practical sizing tips

• Add up your target simultaneous flows and the temperature rise you need. As a quick rule of thumb, an 18kW unit offers about a 60°F rise at 2 GPM and about 40°F at 3 GPM.
  
• Use low‑flow showerheads (1.5–1.8 GPM) to keep the system within its best performance envelope.
  
• Keep the setpoint near 120°F; it’s safe, efficient, and reduces mixing complexity at the tap.

Recommendation

I recommend the Orbek 18kW tankless for households that match its strengths: small to mid‑size homes in moderate climates, or any home willing to pair it with low‑flow fixtures and realistic simultaneous use. It’s compact, quiet, and impressively stable on temperature. The install is clean if you plan the electrical properly, and the safety and certification boxes are genuinely checked.

If you need three heavy draws at once in winter, step up in capacity or look at gas. But for the many scenarios where one to two fixtures run at a time, this unit delivers consistent, comfortable hot water and gives valuable space back—without the wasted energy of keeping a tank warm all day.