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Written from the listing's specs, not from our own use · How we rate
A 5.1 GPM maximum flow, Wi-Fi control from your phone and freeze protection: the MIZUDO 120,000 BTU Propane covers what matters most in a gas tankless heater. It suits a one-bathroom home or a small apartment, and its sibling listing, the MIZUDO 199,000 BTU Natural Gas Indoor, holds #1 in our indoor natural gas tankless water heater ranking.
These are sold as variants of one listing family. Each variant has its own page.
| Brand | MIZUDO |
|---|---|
| Category | Gas tankless water heaters |
| Fuel | Propane |
| Stated maximum flow | 5.1 GPM |
| Stated gas input | 120,000 BTU/h |
| Vent size | 3" |
| Freeze protection | Stated in the listing |
| Wi-Fi | Built in, per the listing |
| Stated warranty | 2 years |
| ASIN | B0F99QVQ84 |
Full listing title: MIZUDO 120,000 BTU Propane Tankless Water Heater Max 5.1 GPM,WiFi&APP
| Fuel | PropaneFull listing title |
|---|---|
| Stated maximum flow | 5.1 GPMFull listing title |
| Stated gas input | 120,000 BTUFull listing title |
Rated from the listing's specs, no buyer reviews yet
What it's made for: a one-bathroom home or a small apartment.
Two gas tankless heaters on propane too, with about the same flow, closest to it on our rating, each with a dated price.
That's the maximum flow the listing states, and headline flows are usually quoted at a mild temperature rise. Up north in winter, 42 °F water has to climb 63 °F to reach a 105 °F shower, and the flow drops with it. Ask for the flow chart and read that line. Our calculator counts a shower at 2 GPM, so on paper 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
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.
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.
Propane: that's what the listing names. A propane unit runs off a tank outside, so the tank size and the regulator are part of the plan.
Natural gas: 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; ask before you order.
The seller states, word for word, in the MIZUDO 120,000 BTU Propane listing:
Manage your tankless water heater propane remotely through the dedicated mobile application.
Constructed with industrial-grade materials including phosphorous-deoxidized copper heat exchanger and stainless steel combustion chamber.
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.
What the MIZUDO 120,000 BTU Propane listing names:
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 120,000 BTU Propane 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.
At the price on Sep 30, 2026, each GPM of stated maximum flow works out at about $105.88 (price ÷ stated GPM, our arithmetic). That puts it in the cheaper third of the 10 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 B0F99QVQ84), where today's price, stock and seller apply. Sizes and variants of the same family often sit at different prices.
Two showers and the dishwasher at once? The Rheem RTG 8.4 GPM Propane Outdoor (7.5/10) states up to 8.4 GPM.
Want the high-efficiency kind? The ThermoMate Condensing Propane (7.6/10) is a condensing unit rated 0.86 UEF, per its listing.
On natural gas, not propane? The ThermoMate Condensing Natural Gas (7.7/10) runs on natural gas.
Our take
What we'd buy the MIZUDO 120,000 BTU Propane for is a 5.1 GPM maximum flow, with Wi-Fi control from your phone as a bonus. Nobody has posted a buyer review we could count yet, so the listing is all we have to go on. Honestly, the catch: no stated temperature hold, while most picks here claim ±1 °F. We'd pick it if you like to see what your appliances are doing; otherwise, put it next to the ThermoMate Condensing Natural Gas first.
Old tank out, unit on the wall, vent through the wall or the roof (3" pipe, per the listing). Plan the gas line for 120,000 BTU/h; a licensed pro handles it, and often a permit.
Hot water arrives after the cold already in the pipes, then stays. A trickle from a bathroom tap may not light the burner; open it a bit more.
January water comes in colder, so the same unit gives fewer GPM. Stagger the showers if you sized it tight.
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.
Before the MIZUDO 120,000 BTU Propane ships, check your gas line: 120,000 BTU/h is a lot of gas at once, so ask your plumber whether the existing line can feed it.
5.1 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.
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.
2 years are stated. Read what it requires: a licensed install, the gas type and regular flushing are the usual conditions.
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 the MIZUDO 120,000 BTU Propane stacks up against the closest alternative, the ThermoMate Condensing Natural Gas.
| Criterion | MIZUDO 120,000 BTU Propane | ThermoMate Condensing Natural Gas |
|---|---|---|
| Our rating | 7.6/10 | 7.7/10 |
| Max flow | 5.1 GPM | 5.28 GPM |
| Gas input | 120,000 BTU/h | 114,000 BTU/h |
| Efficiency | Not stated | Condensing, 0.86 UEF |
| Temperature hold | Not stated | ±1 °F stated |
Pick the ThermoMate Condensing Natural Gas if you want our higher-rated option (7.7/10), with more flow (5.28 GPM) and a condensing design; stay with the MIZUDO 120,000 BTU Propane for a bigger burner (120,000 BTU/h).
We rate it 7.6/10 (very good). The rating comes from its documented listing alone, as no customer-review record is captured yet.
The listing states a maximum flow of 5.1 GPM and a gas input of 120,000 BTU/h. 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.
Its listing states up to 5.1 GPM, Wi-Fi control from your phone 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.
Your winter flow: 5.1 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.
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.
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.