forimo Tankless Water Heater Natural Gas,4.21GPM 16L Indoor,Instant Hot Gas Water Heater, with Fahrenheit Digital Display,Multi-Protection

Why I tried this budget tankless

I needed a compact, indoor natural-gas tankless to replace a tired mid-BTU unit in a small apartment. Space was tight, venting options were limited, and I wasn’t keen on spending premium-brand money for what amounts to a one-bath setup with occasional kitchen overlap. The forimo tankless ticked the boxes on paper: 68,000 BTU, 4.21 GPM claimed, steady temperature control, and a stainless-and-copper build with basic safety protections. After installing and living with it, here’s how it actually performed.

Design and capacity, in practical terms

At 68,000 BTU, this is a modest-capacity heater by modern whole-home standards. The headline 4.21 GPM is realistic only at a small temperature rise. For reference, the math works out like this:

• At a 70°F rise (say 45°F inlet to 115°F shower), you’re closer to about 2.0 GPM.
• At a 50°F rise (warmer inlet), around 2.7 GPM.
• That means one shower plus a sink is comfortable in many regions; two showers at once is a stretch unless your inlet water is warm.

In my case (mid-50s°F inlet), the forimo heater easily handled a single shower and intermittent kitchen use, but running a shower and laundry together exposed its limits. It’s best suited for small apartments, cabins, or outbuildings rather than a full, multi-bath home in a cold climate.

Despite the modest BTU, the temperature regulation is the standout. Set a target on the front display and the unit modulates gas and flow nicely to hold that setpoint. “Cold-water sandwiches” (brief bursts of cool water) were mild and shorter than I expected for this price class.

One quirk: the spec claims an upper limit of 167°F. In my testing, the unit capped out around 150°F. That’s more than sufficient for domestic hot water and arguably safer from a scald perspective, but if you’re eyeing it for hydronic radiators or other high-temp applications, know that it tops out below the marketing number.

Installation: doable, but budget an extra run to the store

This is a straightforward install if you’re replacing something similar. It uses 1/2" NPT water and gas connections, and my gas supply size was fine for 68k BTU. The included vent collar is 2.5" and a short horizontal section is provided; sourcing additional 2.5" vent parts was trickier than the more common 3" or 4" sizes. Factor that into planning.

A few notes from my install:

• I needed a couple of adapters for the water side due to valve orientation and my existing plumbing. Nothing exotic, just be ready for a hardware-store run.
• The unit I received is clearly labeled for natural gas only. Don’t assume it can be converted for propane; it’s not set up for that out of the box.
• It requires a standard 120V outlet for ignition, the control board, anti-freeze functions, and the exhaust fan. Place it where you have power available.
• For winterizing, you’ll want a drain plan. The manual’s guidance to open the pressure relief and drain residual water is sound if you’ll leave it unused in freezing weather.

If you’re not familiar with venting codes for gas appliances, involve a pro. This is a non-condensing design; flue gases are hot and require appropriate materials and clearances.

Noise, start-up, and everyday use

Start-up is quick—usually two to three seconds from opening a hot tap to ignition. There’s a brief whoosh from the fan and burners but the overall noise level is modest. At low trickle flows, the unit will shut off as expected; this is normal for tankless units with a minimum activation flow. I found the flow sensor responsive enough to avoid the on/off cycling that plagues some budget heaters during handwashing.

The front-facing digital display is simple and readable, with Fahrenheit temperature setpoints and status icons. Once set, I rarely touched it; family members appreciated not having to fiddle with gas and water mixing—just pick a temperature and go.

Safety and venting matter (a lot)

The heater includes the basic protections you’d expect: flame-failure shutoff, overheat protection, and anti-freeze modes. Those are welcome, but they don’t replace proper installation:

• Venting: Use code-compliant venting and termination, with the right materials for a non-condensing appliance. The included short section won’t suffice for most installs.
• Combustion air: This is not a magic “hang it anywhere” solution. Follow clearance and ventilation requirements carefully.
• CO monitoring: Put a carbon monoxide detector near any fuel-burning appliance, full stop.

Do those things, and this unit can run safely. Skip them, and you’re taking unnecessary risks.

Build quality and serviceability

Externally, the stainless shell looks tidy and resists smudges better than expected. Internally, you get a copper heat exchanger, straightforward burner layout, and off-the-shelf-looking sensors and valves. It’s not a premium design, but it’s not junky either.

Where the budget roots show is documentation and parts support. The manual covers basic installation and error codes but is thin on component-level details. I asked the seller about replacement parts availability and got a limited, slow response. Plan on going through the seller rather than a nationwide service network if you ever need a flow sensor, ignition module, or gas valve. If uptime is critical or you’re not comfortable with DIY troubleshooting, that’s a trade-off to consider.

Performance over time

After initial setup and a few days of dialing in the temperature, the forimo heater settled into a predictable rhythm. Hot water delivery was consistent for showers and sinks, and modulation kept outlet temperature stable even with minor pressure fluctuations. Over several weeks, I had one ignition lockout tied to a low-flow situation; closing and reopening the tap cleared it. No leaks, no odd noises, and no burner sooting observed.

I do recommend installing isolation valves and service ports so you can descale the heat exchanger annually (or more often in hard water). That’s standard practice with any tankless and will extend the life of the unit.

Efficiency and operating costs

Being tankless, there’s no standby loss, which is an immediate efficiency win over storage tanks. This is not a condensing unit, so don’t expect top-tier efficiency; think “better than a tank, not as good as a high-end condensing tankless.” The upside of the lower BTU rating is lower peak gas draw and quieter operation, which fits small-space installations well.

Who it’s for—and who should look elsewhere

Good fit:
- Small apartments, cabins, studios, or a single-bath home with modest simultaneous demand
- Budget-conscious installs where you can accept basic documentation and limited parts pathways
- Replacements for similar-size units when you already have compatible venting and gas supply

Look elsewhere:
- Cold-climate homes expecting two showers plus laundry running at the same time
- Anyone who needs broad, fast parts availability and robust, brand-backed tech support
- Applications requiring sustained outlet temps above 150°F or specialized vent configurations

The bottom line

The forimo tankless is a competent, small-capacity indoor natural-gas water heater with stable temperature control, reasonable noise levels, and straightforward installation for the mechanically inclined. It hits its stride in modest-demand scenarios, and it’s a genuine upgrade over a storage tank if space and standby losses are concerns.

Its limitations are clear: capped output relative to mainstream tankless units, documentation that leaves you wanting more, and murky parts/service pathways. I can live with those constraints in a budget install, but I wouldn’t spec this as the backbone of a high-demand household or for anyone who values strong manufacturer support above all else.

Recommendation: I recommend the forimo heater for small, budget-conscious installations where one-bath performance, stable temperatures, and compact size are the priorities—and where the installer understands proper venting and code compliance. If you need higher capacity, a rock-solid warranty, and easily sourced parts, spend more on a well-established brand and treat this as a secondary option rather than your primary hot water workhorse.