Mizudo 4.3
Amazon customer rating as of
Tankless Geek editorial score: 3.9/5
The Mizudo 4.3 is a budget indoor natural-gas tankless: 100,000 BTU/h, up to 4.3 GPM, a UEF just over 0.81, and an oxygen-free copper heat tank for efficient transfer and corrosion resistance. It runs on 120V for its controls, uses a 3-inch power vent, and offers a touch panel with LED display, a 95–149 °F range, and ±1 °F temperature control, plus overheat and flame-failure protection with CSA certification. Mizudo rates it for two to three fixtures — up to two showers at once depending on inlet temperature.
As a non-condensing unit it's inexpensive and needs no condensate drain, but uses more gas per gallon than a condensing model and must be properly vented. At 100,000 BTU it holds its 4.3 GPM in warm climates and drops toward two GPM in the cold. With a modest but positive review base (~4.3 stars), owners like the value, LED touch controls, and steady temperature. For a small home or apartment wanting simple, affordable gas hot water, it delivers the essentials without frills.
Key Features
Best Use Cases
Our Verdict
A no-frills budget indoor gas tankless for a small home or apartment — LED touch control and an oxygen-free copper exchanger are nice touches at the price. Non-condensing and modest in capacity, best for warm/mild climates that can vent it properly. Value-first buyers get the essentials done.
Technical Specifications
| Input | 100,000 BTU/h (natural gas) |
|---|---|
| Max flow | Up to 4.3 GPM (2–3 fixtures) |
| Efficiency | ≈0.81 UEF, non-condensing |
| Heat exchanger | Oxygen-free copper |
| Controls | Touch panel + LED; 95–149 °F, ±1 °F |
| Venting | 3" power vent; CSA certified |
Specifications verified against the linked source documents. See Sources below.
How much hot water you'll actually get
Usable flow drops as incoming water gets colder. Figures are calculated from rated output (100,000 BTU × 0.81 UEF) and labeled as such — not bench-tested by us.
| Temperature rise | Typical scenario | Usable flow |
|---|---|---|
| 35 °F | Warm climate (75 °F in → 110 °F) — capped at max | 4.3 GPM |
| 45 °F | Mild climate (65 °F in → 110 °F) | 3.6 GPM |
| 60 °F | Cool climate (50 °F in → 110 °F) | 2.7 GPM |
| 70 °F | Cold climate (40 °F in → 110 °F) | 2.3 GPM |
Usable flow at a 110 °F target: BTU × thermal-eff ÷ (ΔF × 500), capped at the 4.3 GPM maximum (non-condensing ~81%).
Pros
Cons
Buy it if…
- Small homes and apartments on a tight budget
- Warm/mild climates needing 2–3 fixtures
- Buyers who want LED touch control at a low price
- Tank replacements where a condensing unit isn't in budget
Skip it if…
- Cold climates needing full 4.3 GPM in winter
- Efficiency-focused buyers (this is non-condensing)
- Whole-home use with many simultaneous fixtures
Installation Requirements
Professional vs DIY
Gas and power-venting are best left to a licensed installer; a permit is usually required.
Gas and electrical work should be done by a licensed professional, and most installs require a permit and must meet local building codes — DIY work can void the manufacturer warranty. Always confirm the unit's own manual for exact clearances, venting, and sizing.
What owners report
Themes summarized from retailer customer feedback (4.3/5 Amazon customer rating, 58 ratings, as of 2026-09-06). These are owner opinions, not our own bench testing.
Owners cite genuine gas hot water at a budget price, with the LED touch panel a welcome extra in this class.
The ±1 °F control and oxygen-free copper exchanger draw praise for consistent output in normal use.
As a combustion appliance it needs correct 3-inch power venting and gas sizing; a competent install matters.
With a smaller review base, long-term durability and support are less proven than mainstream names.
Mizudo 4.3 FAQ
How many fixtures can the Mizudo 4.3 run?+
Up to about 4.3 GPM — two to three fixtures, or up to two showers, in warm climates, tapering as inlet water gets colder.
Does it need electricity?+
Yes — it uses a 120V connection for its controls and power venting, so it isn't a power-free unit.
Is it condensing?+
No — it's non-condensing at roughly 0.81 UEF. No condensate drain, but it needs 3-inch power venting and uses more gas per gallon than a condensing unit.
What temperature range does it offer?+
95–149 °F with ±1 °F precision via the touch panel, giving fine control for showers and household tasks.
What venting does the Mizudo 4.3 require?+
As a non-condensing indoor unit it uses a 3-inch power vent and is CSA certified. Non-condensing exhaust runs hot, so it needs stainless Category III venting routed through a wall or roof with the manufacturer's required clearances — not standard PVC. It also needs a 120 V outlet to run the vent fan and touch controls. There's no condensate drain to plumb because it doesn't condense flue gases. Between the gas connection and the power venting, this is a job for a licensed installer.
What hot-water flow can the Mizudo 4.3 sustain in winter?+
The 4.3 GPM rating assumes a warm inlet. Estimated from its 100,000 BTU/h natural-gas input at about 0.81 efficiency, realistic usable flow is roughly 3.6 GPM at a mild 45 °F rise and about 2.3 GPM at a 70 °F winter rise. That's comfortable two-fixture capacity in mild climates, tightening to one strong shower where groundwater is cold. It's genuinely a two-to-three-fixture heater for a small home, not a large or cold-climate house — size it against your coldest incoming water temperature rather than the headline flow.
Product sources
Specifications verified 2026-09-06. Manufacturer documents are treated as the primary source for model specifications. Retailer pages are used only for customer ratings and owner-feedback themes.
- Mizudo 4.3 GPM 100k BTU NG — official site (accessed 2026-09-06)
- Mizudo 4.3 NG — Amazon listing & specs (accessed 2026-09-06)
- Mizudo Comfortech Classic NG — Lowe's (accessed 2026-09-06)
Price range from leading retailers
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