Product images: Amazon listings

ThermoMate CZ422NG Natural Gas Indoor Review

Name: ThermoMate CZ422NG Natural Gas Indoor
Brand: ThermoMate
SKU: B0DRDBDS57

6.8Good · out of 10Not in our top-5 rankings

Written from the listing and 161 buyer reviews, not from our own use · How we rate

On paper, the ThermoMate CZ422NG Natural Gas Indoor gets the important things right: up to 5 GPM, a 0.81 UEF rating and temperature held within ±1 °F. 161 buyers rate it 4.2/5, and it suits one shower at a time and not much more.

Price$399.99Price on Sep 30, 2026 · may have changed

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

Compare side by side ↗

Specifications

Brand	ThermoMate
Category	Gas tankless water heaters
Fuel	Natural gas
Stated mounting location	Indoor
Stated maximum flow	5 GPM
Stated gas input	113,000 BTU/h
Stated voltage	120 V
Stated efficiency	0.81 UEF
Temperature hold	±1 °F, per the listing
Vent size	3"
Freeze protection	Stated in the listing
Buyer reviews	161 · 4.2/5
ASIN	B0DRDBDS57

Full listing title: ThermoMate CZ422NG, Natural Gas Tankless Water Heater Indoor, Up to 5 GPM

Listing evidence

Fuel	Natural Gas Full listing title
Stated mounting location	Indoor Full listing title
Stated maximum flow	5 GPM Full listing title
Stated gas input	113,000 BTU Listing text
Stated voltage	120V Listing text

Updated October 2026

Exact listing, ASIN B0DRDBDS57

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 ↗

ThermoMate CZ422NG Natural Gas Indoor

6.8Good · out of 10$399.99 Price on Sep 30, 2026 · may have changed

Stated: 5 GPM · 113,000 BTU/h · 120 V
161 buyer reviews
Gas tankless water heaters

This product ↑

APUS 95,000 BTU Natural Gas Indoor

6.8Good · out of 10$299.99 Price on Sep 30, 2026 · may have changed

Stated: 4.42 GPM · 95,000 BTU/h · 120 V
141 buyer reviews
Gas tankless water heaters

See the review ↗

Vancepic 100,000 BTU Natural Gas Indoor

7.1Good · out of 10$259.99 Price on Sep 30, 2026 · may have changed

Stated: 4.3 GPM · 100,000 BTU/h
Gas tankless water heaters

See the review ↗

Up to 5 GPM from a 113,000 BTU burner

That's the maximum flow the listing states, and headline flows are usually quoted at a mild temperature rise. A cold January asks for a 63 °F rise (42 °F in, 105 °F out), and at that rise every tankless gives less than its headline; the maker's chart says how much. Counting 2 GPM per shower, as our calculator does, that's one shower and a sink at a time, maybe two showers where the water comes in warm.

What it has going for it

What changes in the morning shower rush

0.81 UEF. Uniform Energy Factor is the federal efficiency label: the higher it is, the less gas or power goes up the vent instead of into your shower.

±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.

One shower at a time, or two?

One at a time, plus the kitchen tap: 5 GPM covers that on paper.

Two at once: fine on a warm day in the South. In January up north, the second shower is where it runs out, so check the flow chart at a 63 °F rise.

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…

You want the high-efficiency kind: the listing doesn't call it condensing
The far bathroom already waits a minute for hot water: no built-in recirculation is named
You want the warranty terms in writing: the listing gives no number of years

What ThermoMate promises

The seller states, word for word, in the ThermoMate CZ422NG Natural Gas Indoor listing:

The ThermoMate instant water heater delivers hot water on-demand for two showers at the same time, maintaining a stable 105°F (based on 65°F inlet temperature).
The freeze protection automatically activates at 41°F (5°C).
Built with an oxygen-free copper heat exchanger for efficient heat transfer and corrosion resistance, this natural gas water heater delivers up to 98% thermal efficiency with a UEF of 0.81.
Easily adjust water temperature (90–140°F) and keep track of flow, fan, and flame status on the 3.5-inch LED display.

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.

ThermoMate CZ422NG Natural Gas Indoor, view 3

Gas, venting and what's in the box

What the ThermoMate CZ422NG Natural Gas Indoor listing names:

Up to 5 GPM
113,000 BTU/h input
Natural gas
Indoor mounting
0.81 UEF
3" vent
120 V plug for the controls
±1 °F temperature hold claimed
Freeze protection named
CSA, ETL or UL mark named

For the ThermoMate CZ422NG Natural Gas Indoor, the installation manual settles the venting, the gas line and the clearances.

ThermoMate CZ422NG Natural Gas Indoor, view 4

Price and cost per GPM of stated flow

$399.99 Price on Sep 30, 2026 · may have changed

At the price on Sep 30, 2026, each GPM of stated maximum flow works out at about $80.00 (price ÷ stated GPM, our arithmetic). That puts it in the cheaper third of the 45 indoor gas tankless heaters we have a price and a stated flow for.

The heater is often the smaller half of the bill: the venting, a gas line that may need upsizing and a licensed installer's day come on top.

The button opens the exact listing (ASIN B0DRDBDS57), where today's price, stock and seller apply.

ThermoMate CZ422NG Natural Gas Indoor, view 5

A better fit for your house?

Two showers and the dishwasher at once? The Ranein 190,000 BTU Natural Gas Indoor (7.9/10) states up to 8.5 GPM.

No easy route for a vent pipe? The LiberLive 130,000 BTU NG Outdoor, Gray (7.3/10) mounts on an outside wall, per its listing.

Want the high-efficiency kind? The ThermoMate Condensing Natural Gas (7.7/10) is a condensing unit rated 0.86 UEF, per its listing.

Our take

The verdict

We like the ThermoMate CZ422NG Natural Gas Indoor for up to 5 GPM and a 0.81 UEF rating. 161 buyers give it 4.2/5, good but not spotless. The catch with this ThermoMate indoor gas tankless heater: no word on the warranty. Before you decide, put it next to the APUS 95,000 BTU Natural Gas Indoor.

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 (3" pipe, per the listing). Plan the gas line for 113,000 BTU/h; 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 4.2/5, a solid record, slightly below our ranked picks' 4.3 average. 161 reviews is a fair sample, enough for the average to mean something.

The numbers

Buyer rating: 4.2/5
Reviews: 161
Ranked picks' average: 4.3/5

The one thing we'd check first

Before you order the ThermoMate CZ422NG Natural Gas Indoor, check your gas line: 113,000 BTU/h is a lot of gas at once, so ask your plumber whether the existing line can feed it.

Before you buy

Your winter flow

5 GPM is the headline. In a northern January the water comes in near 42 °F, so a 105 °F shower needs a 63 °F rise and the real flow drops. Our flow-rate calculator runs the numbers for your house.

Vent and gas line

Ask the plumber to check the gas line size and the meter against the heater's input, and to quote the vent route at the same visit. Our install cost guide shows what that usually adds.

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 ThermoMate CZ422NG Natural Gas Indoor stacks up against the closest alternative, the APUS 95,000 BTU Natural Gas Indoor.

Criterion	ThermoMate CZ422NG Natural Gas Indoor	APUS 95,000 BTU Natural Gas Indoor
Our rating	6.8/10	6.8/10
Max flow	5 GPM	4.42 GPM
Gas input	113,000 BTU/h	95,000 BTU/h
Buyer reviews	161 · 4.2/5	141 · 4.4/5

Both score 6.8/10. The APUS 95,000 BTU Natural Gas Indoor adds a higher buyer rating (4.4/5), while the ThermoMate CZ422NG Natural Gas Indoor brings more flow (5 GPM) and a bigger burner (113,000 BTU/h).

Compare side by side ↗See the APUS 95,000 BTU Natural Gas Indoor review →

The score in detail

How we rated it

Our score: 6.8/10

Buyer rating (45%)

37.8 / 45

4.2/5 average

Review volume (35%)

20.9 / 35

161 buyer reviews

Documented specifications (20%)

9.4 / 20

47/100 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 for this exact listing, 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 ThermoMate CZ422NG Natural Gas Indoor any good?

We rate it 6.8/10 (good). It is based on 161 buyer reviews averaging 4.2/5 and the specifications stated in the listing.

How much hot water can the ThermoMate CZ422NG Natural Gas Indoor deliver?

The listing states a maximum flow of 5 GPM and a gas input of 113,000 BTU/h 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 ThermoMate CZ422NG Natural Gas Indoor 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.

What do you get with the ThermoMate CZ422NG Natural Gas Indoor?

Its listing states up to 5 GPM, a 0.81 UEF rating, 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 ThermoMate CZ422NG Natural Gas Indoor?

Your winter flow: 5 GPM is the headline. In a northern January the water comes in near 42 °F, so a 105 °F shower needs a 63 °F rise and the real flow drops. Our flow-rate calculator runs the numbers for your house. Vent and gas line: ask the plumber to check the gas line size and the meter against the heater's input, and to quote the vent route at the same visit. Our install cost guide shows what that usually adds. 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 ThermoMate CZ422NG Natural Gas Indoor?

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 ThermoMate CZ422NG Natural Gas Indoor yourselves?

No, we haven't used it ourselves. Everything on this page comes from its listing and 161 buyer reviews, read line by line and weighed with our published formula.

Gas tankless water heaters ↗All ThermoMate products Comparison tool All product reviews