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MIZUDO 199,000 BTU Natural Gas Indoor

Product images: Amazon listings

MIZUDO 199,000 BTU Natural Gas Indoor Review

9.2Excellent · out of 10#1 of 5 in our Indoor Natural Gas Tankless Water Heaters ranking

Written from the listing and 307 buyer reviews, not from our own use · How we rate

If you're after up to 10.3 GPM, the MIZUDO 199,000 BTU Natural Gas Indoor delivers, with temperature held within ±1 °F and app control on top. It tops our indoor natural gas tankless water heater ranking, and it's made for swapping a 50-gallon tank for a house with three bathrooms.

Variants of this model

These are sold as variants of one listing family. Each variant has its own page.

Price$1,199Price on Sep 30, 2026 · may have changed
Check the price on Amazon ↗ MIZUDO 199,000 BTU Natural Gas Indoor (opens in a new tab)Affiliate link · price and stock on Amazon
Compare side by side ↗
Specifications
BrandMIZUDO
CategoryGas tankless water heaters
FuelNatural gas
Stated mounting locationIndoor
Stated maximum flow10.3 GPM
Stated gas input199,000 BTU/h
Stated voltage120 V
Temperature hold±1 °F, per the listing
Vent size5"
Wi-FiBuilt in, per the listing
Stated warranty2 years
Buyer reviews307 · 4.4/5
ASINB0GDF9QT35

Full listing title: MIZUDO Natural Gas Tankless Water Heater, 199,000 BTU, Indoor

Listing evidence
FuelNatural Gas Full listing title
Stated mounting locationIndoor Full listing title
Stated maximum flowUp to 10.3 GPM Listing text
Stated gas input199,000 BTU Full listing title
Stated voltage120V Listing text
Updated October 2026
Exact listing, ASIN B0GDF9QT35
Rating from a published formula

Compared with its closest rivals

The two picks next to it in our indoor natural gas tankless water heaters ranking, with their rating and a dated price.

Compare side by side ↗

MIZUDO 199,000 BTU Natural Gas Indoor

MIZUDO 199,000 BTU Natural Gas Indoor

9.2Excellent · out of 10$1,199 Price on Sep 30, 2026 · may have changed
  • Stated: 10.3 GPM · 199,000 BTU/h · 120 V
  • 307 buyer reviews
  • Gas tankless water heaters
This product ↑
Ranein 190,000 BTU Natural Gas Indoor

Ranein 190,000 BTU Natural Gas Indoor

7.9Very good · out of 10$699 Price on Sep 30, 2026 · may have changed
  • Stated: 8.5 GPM · 190,000 BTU/h
  • 710 buyer reviews
  • Gas tankless water heaters
See the review ↗

Up to 10.3 GPM from a 199,000 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. Counting 2 GPM per shower, as our calculator does, that's room for three showers at once, fewer when January water comes in cold.

Why it made our list

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.

Wi-Fi app. Set the temperature, see the flow and get error codes on your phone, which beats reading a blinking code in the crawl space.

One shower at a time, or two?

Two at once: up to 10.3 GPM, and our calculator counts a shower at 2 GPM, so that's two showers and a tap on paper. The January answer is in the flow chart, on the 63 °F rise line.

One at a time: then it's more heater than you need, with the gas line and the vent to match. A smaller unit may do the job for less.

Great for you if…

  • You want our #1 indoor natural gas tankless water heater
  • Two showers and the dishwasher run at the same time in your house
  • A shower that suddenly runs cold drives you mad
  • You trust a long track record: 307 buyer reviews

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

What MIZUDO promises

The seller states, word for word, in the MIZUDO 199,000 BTU Natural Gas Indoor listing:

  • Advanced gas modulation of water heater helps maintain water temperature within ±1°F, reducing sudden hot-and-cold fluctuations.
  • The gas tankless water heater responds to lower-flow hot water supply for faucets, showers, and other fixtures.
  • In addition to the LED display, you can manage your gas water heater from anywhere via App: check operating status, fine-tune temperature, and get instant abnormal alerts.
  • The sealed concentric direct-vent system of this tankless gas water heater draws outdoor air for combustion and uses a dedicated 3" × 5" concentric vent kit.
  • It uses a standard 120V power supply with 3/4" NPT connections.

Their words and their figures, not our measurements. How steady your shower stays when someone opens the kitchen tap, and what's left of that flow in January, no listing can tell you.

MIZUDO 199,000 BTU Natural Gas Indoor, view 3

Gas, venting and what's in the box

What the MIZUDO 199,000 BTU Natural Gas Indoor listing names:

  • Up to 10.3 GPM
  • 199,000 BTU/h input
  • Natural gas
  • Indoor mounting
  • 5" vent
  • ±1 °F temperature hold claimed
  • Wi-Fi app control
  • CSA, ETL or UL mark named

Warranty & support: 2-year warranty, as stated in the listing · CSA, ETL or UL certification named in the listing.

That is the maker's promise, not ours. Keep the invoice, register the MIZUDO 199,000 BTU Natural Gas Indoor if the maker asks, and read the install conditions: many tankless warranties need a licensed install and regular flushing.

Read the installation manual for the vent, the gas line size and the clearances before you order; it overrides anything above.

MIZUDO 199,000 BTU Natural Gas Indoor, view 4

Price and cost per GPM of stated flow

$1,199 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 $116.41 (price ÷ stated GPM, our arithmetic). That puts it around the middle of the 45 indoor gas tankless heaters we have a price and a stated flow for.

The online price is the heater alone. Venting, a bigger gas line where needed and the installer's day are a separate bill, often as big as this one.

The button opens the exact listing (ASIN B0GDF9QT35), where today's price, stock and seller apply. Sizes and variants of the same family often sit at different prices.

MIZUDO 199,000 BTU Natural Gas Indoor, view 5

A better fit for your house?

No easy route for a vent pipe? The A. O. Smith 10 GPM Natural Gas Outdoor (8.0/10) mounts on an outside wall, per its listing.

Want the high-efficiency kind? The Rinnai RU199iN Condensing (7.8/10) is a condensing unit, per its listing.

On propane, not natural gas? The Rheem RTGH 9.5 GPM Propane Indoor (7.8/10) runs on propane.

Our take

The verdict

Of everything in our indoor natural gas tankless water heater ranking, the MIZUDO 199,000 BTU Natural Gas Indoor is the one we'd order first. 307 buyers back that up with 4.4/5, about as reassuring as a review record gets. Where it falls short: the headline GPM is a mild-weather figure, so leave yourself margin for January. If the flow holds up at your winter rise and the install quote makes sense, it's the one we'd put on the wall. If not, the Ranein 190,000 BTU Natural Gas Indoor is plan B.

Check the price on Amazon ↗ MIZUDO 199,000 BTU Natural Gas Indoor (opens in a new tab)Affiliate link · price and stock on AmazonSee the indoor natural gas tankless water heaters ranking →

Living with it

Install day

Old tank out, unit on the wall, vent through the wall or the roof (5" pipe, per the listing). Plan the gas line for 199,000 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 4.4/5, a strong record, above this ranking's 4.3 average. And with 307 reviews behind it, that number is hard to argue with.

The numbers
Buyer rating
4.4/5
Reviews
307
This ranking's average
4.3/5

The one thing we'd check first

Before you order the MIZUDO 199,000 BTU Natural Gas Indoor, check your gas line: 199,000 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

10.3 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 warranty terms

2 years are stated. Read what it requires: a licensed install, the gas type and regular flushing are the usual conditions.

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 MIZUDO 199,000 BTU Natural Gas Indoor stacks up against the closest alternative in our ranking, the Ranein 190,000 BTU Natural Gas Indoor.

CriterionMIZUDO 199,000 BTU Natural Gas IndoorRanein 190,000 BTU Natural Gas Indoor
Our rating9.2/107.9/10
Max flow10.3 GPM8.5 GPM
Gas input199,000 BTU/h190,000 BTU/h
Temperature hold±1 °F statedNot stated
Buyer reviews307 · 4.4/5710 · 4.2/5

On our rating, the MIZUDO 199,000 BTU Natural Gas Indoor comes out ahead (9.2 vs 7.9), and it brings more flow (10.3 GPM) and a bigger burner (199,000 BTU/h) on top. Start with this one.

Compare side by side ↗See the Ranein 190,000 BTU Natural Gas Indoor review →
The score in detail

How we rated it

Our score: 9.2/10

Buyer rating (45%)

39.6 / 45

4.4/5 average

Review volume (35%)

23.5 / 35

307 buyer reviews

Documented specifications (20%)

16.4 / 20

82/100 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 shown on this variant's own listing page (not shared with the other MIZUDO variants), 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 MIZUDO 199,000 BTU Natural Gas Indoor any good?

We rate it 9.2/10 (excellent), #1 of 5 in our indoor natural gas tankless water heater ranking. It is based on 307 buyer reviews averaging 4.4/5 and the specifications stated in the listing.

How much hot water can the MIZUDO 199,000 BTU Natural Gas Indoor deliver?

The listing states a maximum flow of 10.3 GPM and a gas input of 199,000 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 MIZUDO 199,000 BTU 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 MIZUDO 199,000 BTU Natural Gas Indoor?

Its listing states up to 10.3 GPM, temperature held within ±1 °F and Wi-Fi control from your phone. 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 MIZUDO 199,000 BTU Natural Gas Indoor?

Your winter flow: 10.3 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 warranty terms: 2 years are stated. Read what it requires: a licensed install, the gas type and regular flushing are the usual conditions. 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 MIZUDO 199,000 BTU 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 MIZUDO 199,000 BTU Natural Gas Indoor yourselves?

No, we haven't used it ourselves. Everything on this page comes from its listing and 307 buyer reviews, read line by line and weighed with our published formula.

Keep comparing

If the MIZUDO 199,000 BTU Natural Gas Indoor hasn't sold you yet, see where it ranks, read the guides that feature it or browse all gas tankless water heaters.

Where it ranks

Best Tankless Water Heaters in 2026 →Best Gas Tankless Water Heaters in 2026 →Best Whole-House Tankless Water Heaters in 2026: Gas and Electric →

Read this before you buy

Tankless water heater buying guide: how to choose one →Gas vs electric tankless water heater: which should you buy? →Tankless water heater sizing: how many GPM do you need? →Natural gas vs propane tankless water heater: which fuel fits? →
Gas tankless water heaters ↗All MIZUDO productsComparison toolAll product reviews