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ThermoMate Condensing Natural Gas Review

Name: ThermoMate Condensing Natural Gas
Brand: ThermoMate
SKU: B0F9Y5ZNVF

7.7Very good · out of 10Rated from the listing's specs, no buyer reviews yet

Written from the listing's specs, not from our own use · How we rate

Up to 5.28 GPM, a condensing design rated 0.86 UEF and temperature held within ±1 °F: the ThermoMate Condensing Natural Gas covers what matters most in a gas tankless heater. Think of it for one shower at a time and not much more: 7.7/10 on what its listing documents.

Price$559.99Price on Sep 30, 2026 · may have changed

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

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Specifications

Brand	ThermoMate
Category	Gas tankless water heaters
Fuel	Natural gas
Stated maximum flow	5.28 GPM
Stated gas input	114,000 BTU/h
Stated voltage	120 V
Condensing design	Stated in the listing title
Stated efficiency	0.86 UEF
Temperature range	90 to 140 °F
Temperature hold	±1 °F, per the listing
Vent size	3"
Freeze protection	Stated in the listing
ASIN	B0F9Y5ZNVF

Full listing title: ThermoMate Condensing Tankless Water Heater Natural Gas, Up to 5.28 GPM

Listing evidence

Fuel	Natural Gas Full listing title
Stated maximum flow	5.28 GPM Full listing title
Stated gas input	114,000BTU Listing text
Stated voltage	120V Listing text
Condensing design	Condensing Full listing title

Updated October 2026

Exact listing, ASIN B0F9Y5ZNVF

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 Condensing Natural Gas

7.7Very good · out of 10$559.99 Price on Sep 30, 2026 · may have changed

Stated: 5.28 GPM · 114,000 BTU/h · 120 V
Gas tankless water heaters

This product ↑

MIZUDO 120,000 BTU Natural Gas

7.6Very good · out of 10$539.99 Price on Sep 30, 2026 · may have changed

Stated: 5.1 GPM · 120,000 BTU/h
Gas tankless water heaters

See the review ↗

Ranein Condensing Natural Gas, 5.1 GPM

7.4Good · out of 10$559 Price on Sep 30, 2026 · may have changed

Stated: 5.1 GPM · 120,000 BTU/h · 120 V
Gas tankless water heaters

See the review ↗

Up to 5.28 GPM from a 114,000 BTU burner

That's the maximum flow the listing states, and headline flows are usually quoted at a mild temperature rise. In January the water comes in nearer 42 °F, so a 105 °F shower needs a 63 °F rise and the unit gives you less; the flow chart in the manual shows how much less. At 2 GPM a shower (our calculator's figure), the headline means 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

Condensing, 0.86 UEF. A second heat exchanger pulls heat out of the exhaust before it leaves, so more of the gas you pay for ends up in the water. The exhaust runs cool enough for plastic vent pipe, and the condensate needs a drain.

±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.

Natural gas or propane?

Natural gas: that's what the listing names, so it runs off the gas line, which may need upsizing for a tankless burner.

Propane: it's a different set of gas jets and pressures. Only the maker's conversion kit, if there is one, and a licensed gas fitter can switch it; buy the propane version instead if you have a tank.

Great for you if…

You care about the gas bill as much as the hot water
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'd rather wait for buyer reviews: none are captured for this listing yet
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 Condensing Natural Gas listing:

Equipped with 4 ceramic heating cores, it auto-activates frost protection when temperatures hit 41°F (5°C).
As a condensing unit, this water heater produces mildly acidic condensate water that you will need to discharge into a drain.
The indoor residential tankless hot water heater features standard 3/4" NPT water inlet/outlet connectors, a 1/2" NPT gas inlet, a 3" OD vent, and a UL-approved 120V plug.

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 Condensing Natural Gas, view 3

Gas, venting and what's in the box

What the ThermoMate Condensing Natural Gas listing names:

Up to 5.28 GPM
114,000 BTU/h input
Natural gas
Condensing, 0.86 UEF
3" vent
120 V plug for the controls
±1 °F temperature hold claimed
90 to 140 °F setpoint
Freeze protection named
CSA, ETL or UL mark named

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

ThermoMate Condensing Natural Gas, view 4

Price and cost per GPM of stated flow

$559.99 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 $106.06 (price ÷ stated GPM, our arithmetic). That puts it around the middle of the 10 gas tankless heaters we have a price and a stated flow for.

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 B0F9Y5ZNVF), where today's price, stock and seller apply.

ThermoMate Condensing Natural Gas, view 5

A better fit for your house?

Two showers and the dishwasher at once? The Rheem RTG 8.4 GPM Propane Outdoor (7.5/10) states up to 8.4 GPM.

On propane, not natural gas? The MIZUDO 120,000 BTU Propane (7.6/10) runs on propane.

Our take

The verdict

The ThermoMate Condensing Natural Gas earns its place with up to 5.28 GPM and a condensing design rated 0.86 UEF. There are no buyer reviews to check it against yet, which makes it a bet on the listing. The one thing that bugs us: no word on the warranty. We'd pick it if you care about the gas bill as much as the hot water; otherwise, put it next to the MIZUDO 120,000 BTU Natural Gas 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 (3" pipe, per the listing). Plan the gas line for 114,000 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), check the condensate drain and the neutralizer, and clean the inlet filter. Our flushing and descaling guide has the checklist.

The one thing we'd check first

Before the ThermoMate Condensing Natural Gas goes in your cart, check your gas line: 114,000 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

5.28 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.

The condensate

A condensing unit drips acidic water that needs a drain, often through a neutralizer. Our condensing guide explains the extra parts.

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 Condensing Natural Gas stacks up against the closest alternative, the MIZUDO 120,000 BTU Natural Gas.

Criterion	ThermoMate Condensing Natural Gas	MIZUDO 120,000 BTU Natural Gas
Our rating	7.7/10	7.6/10
Max flow	5.28 GPM	5.1 GPM
Gas input	114,000 BTU/h	120,000 BTU/h
Efficiency	Condensing, 0.86 UEF	Not stated
Temperature hold	±1 °F stated	Not stated

Pick the MIZUDO 120,000 BTU Natural Gas if a bigger burner (120,000 BTU/h) matters more to you; on our rating, the ThermoMate Condensing Natural Gas comes out ahead.

Compare side by side ↗See the MIZUDO 120,000 BTU Natural Gas review →

The score in detail

How we rated it

Spec-based rating on a 4.5–8.5 scale: 4.5 + average of the 4 criteria × 0.4. Capped at 8.5 because no customer evidence is included.

Key specifications

9 / 10

Build, warranty & certifications

6 / 10

Listing documentation

9 / 10

Fit & compatibility

8 / 10

This product has no captured buyer-review record yet, so its rating comes from the documented listing alone: four criteria scored out of 10 (key specifications; build, warranty and certifications; listing documentation; fit and compatibility), placed on a 4.5–8.5 scale. Read the full methodology.

Read the methodology →

Frequently asked questions

Is the ThermoMate Condensing Natural Gas any good?

We rate it 7.7/10 (very good). The rating comes from its documented listing alone, as no customer-review record is captured yet.

How much hot water can the ThermoMate Condensing Natural Gas deliver?

The listing states a maximum flow of 5.28 GPM and a gas input of 114,000 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.

What do you get with the ThermoMate Condensing Natural Gas?

Its listing states up to 5.28 GPM, a condensing design rated 0.86 UEF, 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 Condensing Natural Gas?

Your winter flow: 5.28 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. The condensate: a condensing unit drips acidic water that needs a drain, often through a neutralizer. Our condensing guide explains the extra parts. 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 Condensing Natural Gas?

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 Condensing Natural Gas yourselves?

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

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