Nessxa Natural Gas Tankless Water Heater, 14L Instant Hot Water Heater with Fahrenheit Digital Display, Indoor Installation Up to 3.7GPM, 95540BTU

What I tested

I installed the Nessxa 14L tankless natural-gas water heater (I’ll call it the Nessxa 14L) to replace a tired 40-gallon storage tank in a small, two-bath home with a typical mix of low-flow fixtures. The goal was simple: cut the wait for hot water, save space, and avoid the standby losses of a tank. After several weeks of daily use, here’s how it performed, what stood out, and a few things to keep in mind.

Installation and setup

This is an indoor, natural-gas-only unit that requires 110V power and Category II stainless-steel venting. That combination means “DIY” isn’t the right approach for most people; I had a licensed plumber handle the gas line sizing, vent routing, and electrical. A few practical notes from the install:

• Gas supply: At 95,540 BTU, the unit isn’t particularly demanding compared to big 150k–200k BTU tankless models, but line size and run length still matter. We verified adequate supply and added a shutoff near the unit.
• Venting: Nessxa specifies a UL-rated stainless Category II vent with a 3° downward slope. The stainless components feel robust and seal up nicely; the slight slope prevents condensate from eroding the vent path. Don’t substitute PVC here—follow Category II requirements.
• Electrical: It needs a standard 110V outlet for ignition and the combustion fan. If the power goes out, you won’t have hot water.
• Water connections: The heater uses 1/2-inch ports. If your existing plumbing is 3/4 inch, plan for adapters or isolation valve kits. I strongly recommend a tankless service valve kit for easy descaling later.

The unit’s footprint is compact, freeing up real space compared to a tank. Mounting was straightforward, and clearances were manageable in a utility closet with adequate combustion air. Expect a half day of professional labor, give or take, depending on your home’s gas and vent access.

Important: this model is natural gas only. There’s no provision advertised for propane conversion.

Build and design

The Nessxa 14L is housed in a sturdy metal shell with a rust-resistant heat exchanger. It’s not a condensing design, but the materials and the stainless venting inspire confidence for indoor duty. Controls are simple: a digital screen with Fahrenheit/Celsius readout (switchable), and clear adjustments for temperature. There’s a post-shutdown fan that runs briefly to cool internals, which I appreciate for component longevity.

Safety-wise, it includes overheat protection (warning at 125°F/52°C), gas leak detection with automatic cutoff, and a 40-minute safety timer to prevent extended dry-fire scenarios. None of these features feel intrusive in everyday use, but they’re sensible guardrails.

Controls and ease of use

I set the temperature at 118°F for daily use, bumping to 120°F when needed. The screen is bright, easy to read, and switching units is instant. The heater reports outlet temperature in real time, which helps diagnose what’s happening when multiple fixtures open or close. There’s a small learning curve with any tankless: you’ll get the most stable results if you set one temperature at the unit and avoid mixing a lot at the faucet. With that approach, the Nessxa 14L held a stable outlet temperature very well.

Performance

The headline figure is 14 L/min (3.7 GPM) at a 25°C (45°F) temperature rise. In practice, actual flow capacity depends on your incoming water temperature and your target setpoint. With 55°F inlet water and a 120°F setpoint (about a 65°F rise), I saw roughly 2.5–2.7 GPM of stable hot water. That’s enough for:

• One standard shower and a sink simultaneously, or
• A high-flow shower alone with headroom, or
• A dishwasher or laundry cycle while someone takes a shower, with sensible fixture choices.

Two simultaneous showers are possible if both are low-flow and you’re willing to set the temperature modestly. If you expect to run multiple high-demand fixtures at once, you’ll want a higher-BTU unit.

“Instant hot water” is accurate at the heater itself—burner response is quick, and the fan ramps smoothly—but remember you still have to clear the cool water sitting in your home’s piping. If you want zero wait at distant taps, plan a recirculation strategy; this model doesn’t include a built-in recirc pump.

Temperature stability impressed me. I didn’t encounter the classic “cold-water sandwich” after routine start/stop cycles, and small flow changes (like someone cracking a second tap) produced minimal fluctuation. Low-flow activation was reliable for handwashing; I didn’t need to “blast” the faucet to trigger heating. Combustion fan noise is present but unobtrusive—easily lost under the sound of running water.

Efficiency and operating cost

The big win over a tank is eliminating standby losses. There’s no burner cycling all day to keep a reservoir hot; you only burn gas when you use hot water. While Nessxa doesn’t publish a thermal efficiency number in the materials I had, the mid-BTU category and non-condensing design put it in the typical efficiency range for basic indoor tankless units. If you want maximum gas savings in a cold climate with heavy hot-water usage, a condensing model may edge this out—but it will cost more up front and usually requires condensate management. For small to mid-size loads, the Nessxa 14L hits a sensible balance of cost, complexity, and day-to-day savings.

Safety and maintenance

Built-in protections are thoughtful:

• Overheat warning at 125°F and user-selectable setpoints up to 131°F
• Gas leak detection with automatic shutoff
• Post-run fan cooling
• 40-minute safety timer

I recommend pairing the install with CO and gas detectors in the utility area and nearby living spaces. As for maintenance, all tankless heaters benefit from periodic descaling—how often depends on water hardness. If you have hard water, budget for an annual flush and consider a scale filter. The tankless design does resist limescale better than a storage tank, but it’s not immune.

Limitations and trade-offs

• Fuel type: Natural gas only. If your home is on propane, this isn’t the right model.
• Electrical dependency: No hot water during power outages.
• Capacity: Strong for small households or supplemental use, but not a whole-home solution for large families with multiple simultaneous high-flow demands.
• 40-minute timer: Unlikely to affect normal showers, but extended soaking or unusually long commercial-type uses could hit the cutoff.
• Venting: Category II stainless is more specialized than the PVC used on many condensing units. That’s not a flaw, just a detail to plan for.

Who it’s for

The Nessxa 14L makes sense if you want to:

• Replace a smaller tank in a one- to two-bath home with moderate simultaneous usage
• Add reliable hot water to a shop, in-law suite, or remote part of the house
• Save space and cut standby losses without moving to a high-BTU, high-cost condensing system
• Keep controls simple while maintaining safety features and stable temperatures

If you need to run two showers, a tub fill, and a dishwasher all at once, step up to a larger unit (or a pair in parallel). If your home is on propane, look for a model designed for LPG or a unit with a manufacturer-approved conversion kit.

The bottom line

After living with the Nessxa 14L, I’m impressed by how quietly and consistently it does the fundamentals: quick ignition, stable outlet temperatures, clear controls, and a sensible safety stack. Installation demands are real—proper gas sizing, stainless Category II venting with the required slope, and a 110V outlet—but once it’s in, day-to-day operation is uncomplicated.

Recommendation: I recommend the Nessxa 14L for small households or supplemental applications that need dependable, on-demand hot water without the cost and complexity of a high-BTU condensing system. It’s compact, thoughtfully built, and delivers steady performance within its capacity. Just size it honestly for your climate and usage, install it professionally to code, and plan for simple annual maintenance. If your demands are heavier or you’re on propane, pick a different model; otherwise, this is a solid, good-value upgrade over a basic tank.