Product images: Amazon listings

SNDOAS 4.23 GPM Natural Gas, Black Review

Name: SNDOAS 4.23 GPM Natural Gas, Black
Brand: SNDOAS
SKU: B0G5116FSS

4.5Fair · out of 10Not in our top-5 rankings

Written from the listing and 34 buyer reviews, not from our own use · How we rate

The SNDOAS 4.23 GPM Natural Gas in Black packs a 4.23 GPM maximum flow, a ±1 °F temperature hold and freeze protection into one indoor gas tankless heater. It suits one shower at a time and not much more, at 4.5/10 on our rating.

Variants of this model

These 34 buyer reviews (4.1/5) are shared by the , White and , Black listings, so they speak for the family more than for one size.

SNDOAS 4.23 GPM Natural Gas, White · White / 4.23GPM 853,00BTU (Indoor) · 4.5/10

See current price ↗Prices change often: the listing shows today's.

Check the price on Amazon ↗Affiliate link · price and stock on Amazon

Compare side by side ↗

Specifications

Brand	SNDOAS
Category	Gas tankless water heaters
Fuel	Natural gas
Stated mounting location	Indoor
Stated maximum flow	4.23 GPM
Stated voltage	120 V
Temperature range	95 to 149 °F
Temperature hold	±1 °F, per the listing
Freeze protection	Stated in the listing
Buyer reviews	34 · 4.1/5, shared by the SNDOAS 4.23 GPM Natural Gas listing family (2 variants)
ASIN	B0G5116FSS

Full listing title: SNDOAS Tankless Water Heater Natural Gas, Up to 4.23 GPM 853,00 BTU, ±1°F Precise Temperature, Anti-Freeze Protection, Oxygen-Free Copper Heat Exchanger, Ultra Quiet, Indoor Whole House

Listing evidence

Fuel	Natural Gas Full listing title
Stated mounting location	Indoor Full listing title
Stated maximum flow	4.23 GPM Full listing title
Stated voltage	120V Listing text

Updated October 2026

Exact listing, ASIN B0G5116FSS

Rating from a published formula

Compared with its closest rivals

Two gas tankless heaters on natural gas too, with about the same flow, closest to it on our rating, each with a dated price.

Compare side by side ↗

SNDOAS 4.23 GPM Natural Gas, Black

4.5Fair · out of 10See current price ↗

Stated: 4.23 GPM · 120 V
34 buyer reviews
Gas tankless water heaters

This product ↑

Novieex 100,000 BTU Natural Gas Indoor

5.7Fair · out of 10$269.97 Price on Sep 30, 2026 · may have changed

Stated: 4.3 GPM · 100,000 BTU/h · 110 V
45 buyer reviews
Gas tankless water heaters

See the review ↗

APUS 80,000 BTU Natural Gas Indoor

6.7Good · out of 10$249.99 Price on Sep 30, 2026 · may have changed

Stated: 3.6 GPM · 80,000 BTU/h · 120 V
141 buyer reviews
Gas tankless water heaters

See the review ↗

Up to 4.23 GPM

That's the maximum flow the listing states, and headline flows are usually quoted at a mild temperature rise. With January water coming in at 42 °F and a 105 °F shower, the rise is 63 °F and the real flow is lower; the maker's flow chart has that number. Our calculator counts a shower at 2 GPM, so on paper that's one shower at a time.

What it has going for it

What changes in the morning shower rush

±1 °F hold. The burner adjusts as the flow changes, so the shower stays where you set it when somebody opens the kitchen tap. On paper, at least: that is the seller's claim.

Freeze protection. Stated in the listing. Useful in a garage, a crawl space or a cabin that sits empty in winter, as long as the unit keeps power.

One shower at a time, or two?

One at a time: that's what 4.23 GPM is for.

Two at once: not with this one. Look at the bigger units further down this page.

Great for you if…

A shower that suddenly runs cold drives you mad
It will live in a garage, a cabin or another cold spot

Skip it if…

Two showers often run at once in your house: 4.23 GPM is a one-shower unit
You want a long review record: only 34 buyer reviews so far
Star ratings come first for you: 4.1/5 is below the 4.3 average of our ranked picks

What SNDOAS promises

The seller states, word for word, in the SNDOAS 4.23 GPM Natural Gas in Black listing:

Built-in anti-freeze device resists -5°C/23°F low temperature.
The smart LED display shows real-time temperature and usage, while maintaining water within ±1°F of your set point (95°F–149°F).
The intuitive panel of this instant water heater displays temperature, settings, error codes, and gas/water consumption.

The seller's claims, quoted as written; we haven't measured any of it. The flow at your winter rise is in the maker's chart, not in the bullet points.

SNDOAS 4.23 GPM Natural Gas, Black, view 3

Gas, venting and what's in the box

What the SNDOAS 4.23 GPM Natural Gas in Black listing names:

Up to 4.23 GPM
Natural gas
Indoor mounting
120 V plug for the controls
±1 °F temperature hold claimed
95 to 149 °F setpoint
Freeze protection named

For the SNDOAS 4.23 GPM Natural Gas in Black, the installation manual settles the venting, the gas line and the clearances.

SNDOAS 4.23 GPM Natural Gas, Black, view 4

Price and availability

See current price ↗

We have no recent price on file for this listing, so we don't print an old one.

Count the install in the budget: vent pipe, possibly a 3/4" gas line, and a licensed plumber or gas fitter.

The button opens the exact listing (ASIN B0G5116FSS), where today's price, stock and seller apply. Sizes and variants of the same family often sit at different prices.

SNDOAS 4.23 GPM Natural Gas, Black, view 5

A better fit for your house?

Two showers and the dishwasher at once? The Rheem RTGH 8.4 GPM Natural Gas Indoor (7.3/10) states up to 8.4 GPM.

On propane, not natural gas? The ThermoMate CZ422LP Propane Indoor (7.8/10) runs on propane.

The far bathroom takes ages to run hot? The Rinnai REP199eN Smart-Circ (7.3/10) has built-in recirculation, per its listing.

Our take

The verdict

Our favourite thing about the SNDOAS 4.23 GPM Natural Gas in Black is a 4.23 GPM maximum flow, closely followed by a ±1 °F temperature hold. Only 34 buyers have rated it so far (4.1/5), so treat the score as an early read. Honestly, the catch: their 4.1/5 average sits under the 4.3 of our ranked picks. We'd pick it if a shower that suddenly runs cold drives you mad; otherwise, put it next to the Rinnai SENSEI CX199iN Commercial first.

Check the price on Amazon ↗Affiliate link · price and stock on AmazonAll gas tankless water heaters →

Living with it

Install day

Old tank out, unit on the wall, vent through the wall or the roof. a licensed pro handles it, and often a permit.

The first shower

Hot water arrives after the cold already in the pipes, then stays (within ±1 °F, per the listing). A trickle from a bathroom tap may not light the burner; open it a bit more.

The first winter

January water comes in colder, so the same unit gives fewer GPM. Stagger the showers if you sized it tight.

Once a year

Flush the heat exchanger with a pump and a descaler (the service valves make it an hour's job), and clean the inlet filter. Our flushing and descaling guide has the checklist.

What buyers say

Buyers give it 4.1/5, a decent record, slightly below our ranked picks' 4.3 average. Only 34 reviews so far, and our formula damps averages built on fewer than 50. The same reviews appear on both variants of the SNDOAS 4.23 GPM Natural Gas family, so they describe the family rather than this exact variant.

The numbers

Buyer rating: 4.1/5
Reviews: 34
Ranked picks' average: 4.3/5

The one thing we'd check first

Before the SNDOAS 4.23 GPM Natural Gas in Black goes in your cart, check your winter flow: 4.23 GPM is a best case, so run your January numbers in our calculator first.

Before you buy

Your winter flow

Count the fixtures that run together on a busy morning (our calculator uses 2 GPM a shower, 1.5 for the kitchen), then compare with the maker's chart. Our sizing guide shows how.

Vent and gas line

A licensed plumber or gas fitter confirms the vent route, the combustion air and a gas line that can deliver its full input. Get that quote before you order; our installation guide lists what they will ask.

Power at the wall

It plugs into a 120 V outlet for its fan and controls, so plan one within reach of where it hangs.

Flushing

Hard water scales the heat exchanger. Service valves on the water lines turn the yearly flush into an hour with a bucket and a pump; our flushing and descaling guide shows the routine.

How it compares

How the SNDOAS 4.23 GPM Natural Gas in Black stacks up against the closest alternative, the Rinnai SENSEI CX199iN Commercial.

Criterion	SNDOAS 4.23 GPM Natural Gas, Black	Rinnai SENSEI CX199iN Commercial
Our rating	4.5/10	4.7/10
Max flow	4.23 GPM	11.1 GPM
Gas input	Not stated	199,000 BTU/h
Efficiency	Not stated	0.98 UEF
Temperature hold	±1 °F stated	Not stated
Buyer reviews	34 · 4.1/5	21 · 4.5/5

Pick the Rinnai SENSEI CX199iN Commercial if you want our higher-rated option (4.7/10), with more flow (11.1 GPM) and a bigger burner (199,000 BTU/h); stay with the SNDOAS 4.23 GPM Natural Gas in Black for a stated ±1 °F hold.

Compare side by side ↗See the Rinnai SENSEI CX199iN Commercial review →

The score in detail

How we rated it

Our score: 4.5/10

Buyer rating (45%)

25.1 / 45

4.1/5 average, confidence-damped (34 reviews < 50)

Review volume (35%)

14.6 / 35

34 buyer reviews, shared by 2 variants

Documented specifications (20%)

5.4 / 20

27/100 listing documentation score

Our rating is an evidence index on a 0–10 scale. It is not a buyer star rating, and we have not used the product ourselves.

Buyer rating (45%): the captured average of the review pool shown on both variants of the SNDOAS 4.23 GPM Natural Gas listing family, damped when there are fewer than 50 reviews.
Review volume (35%): more reviews mean more reliable evidence, on a logarithmic scale up to 5,000 reviews.
Documented specifications (20%): how completely the exact listing documents the attributes that matter.

Our editors then look at how it compares with the other heaters we rate. A commission is never an input to the rating. Read the full methodology.

Read the methodology →

Frequently asked questions

Is the SNDOAS 4.23 GPM Natural Gas in Black any good?

We rate it 4.5/10 (fair). It is based on 34 buyer reviews averaging 4.1/5, shared by the SNDOAS 4.23 GPM Natural Gas listing family (2 variants) and the specifications stated in the listing.

How much hot water can the SNDOAS 4.23 GPM Natural Gas, Black deliver?

The listing states a maximum flow of 4.23 GPM on 120 V. The headline flow is a mild-weather number: with cold winter water coming in, the same unit gives you less. Read the maker's flow chart at your winter rise, or let our flow-rate calculator do the sums.

Can the SNDOAS 4.23 GPM Natural Gas, Black be installed indoors?

Yes, the listing says indoor mounting. That means a vent route to the outside, combustion air and a gas line sized for the unit, all as the maker and your local code require. A licensed plumber or gas fitter sorts that out.

Are the reviews specific to the SNDOAS 4.23 GPM Natural Gas in Black?

No. The same review pool appears on every variant of the SNDOAS 4.23 GPM Natural Gas listing family: 34 reviews averaging 4.1/5 on the SNDOAS 4.23 GPM Natural Gas, White and SNDOAS 4.23 GPM Natural Gas, Black. The count therefore describes the family, not this exact variant, and in our rankings the family takes a single slot.

What do you get with the SNDOAS 4.23 GPM Natural Gas in Black?

Its listing states up to 4.23 GPM, temperature held within ±1 °F and freeze protection. These are the seller's figures, not our measurements: how steady the temperature is in your shower and how it copes with your winter water can't be read from a listing.

What should I check before ordering the SNDOAS 4.23 GPM Natural Gas in Black?

Your winter flow: count the fixtures that run together on a busy morning (our calculator uses 2 GPM a shower, 1.5 for the kitchen), then compare with the maker's chart. Our sizing guide shows how. Vent and gas line: a licensed plumber or gas fitter confirms the vent route, the combustion air and a gas line that can deliver its full input. Get that quote before you order; our installation guide lists what they will ask. Power at the wall: it plugs into a 120 V outlet for its fan and controls, so plan one within reach of where it hangs. Flushing: hard water scales the heat exchanger. Service valves on the water lines turn the yearly flush into an hour with a bucket and a pump; our flushing and descaling guide shows the routine.

Where can I buy the SNDOAS 4.23 GPM Natural Gas in Black?

We link to the exact listing on Amazon, where today's price, stock and seller apply. It is an affiliate link, and it has no effect on the rating.

Have you used the SNDOAS 4.23 GPM Natural Gas in Black yourselves?

No, we haven't used it ourselves. Everything on this page comes from its listing and 34 buyer reviews, read line by line and weighed with our published formula.

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