Five tankless units, scored out of 100 — gas condensing and electric
Every tankless heater is sold on the same brochure number: its flow at a gentle 35°F temperature rise, in warm groundwater, on its best day. Your house does not live on that day. In January, with 50°F water coming in and 120°F water going out, the rise is 70°F — and at that rise the biggest box on this page delivers barely half its headline flow. So this page scores tankless the way our size calculator sizes it: gallons per minute at a 70°F rise, the winter number for most of the country. We work from manufacturer spec sheets and flow curves only. We do not bench-test these units and we will not pretend otherwise; what we do is the math the brochure hopes you skip.
The rubric is the same one published on How We Rate, adapted to tankless: flow at winter rise 30, efficiency 25, running cost and upkeep 25, warranty and parts 20. One structural fact shapes the whole field: the gas brands split by channel. Rinnai sells through dealers and Amazon alike. Navien and Noritz sell through plumbing wholesalers and expect a licensed installer — marketplace listings exist, but both brands can and do question warranty claims on units that arrive outside their channel. That is not a reason to cross them off; it is a reason to buy them the way they are meant to be bought, and their cards below say so plainly.
The shortlist
| Model | Fuel | GPM @ 70°F rise | Score |
|---|---|---|---|
| Navien NPE-240A2 | Gas | 5.6 | 88 |
| Rinnai Sensei RU199iN | Gas | 5.5 | 86 |
| Noritz EZ98DV | Gas | 4.9 | 84 |
| Rheem RTGH-90DVLN-3 | Gas | 5.2 | 83 |
| EcoSmart ECO 27 | Electric | 3.1 | 74 |
Flow at a 70°F rise from each maker’s published flow table or curve; where a maker publishes 67°F instead, that figure is used and the card says so. Specs checked 2026-11-09.
The picks, scored
Navien NPE-240A2
88/100
The strongest all-around gas tankless on the spec sheet. Navien publishes its flow table in the open: 11.2 GPM at a 35°F rise, 5.6 at 70°F — tied for the best winter number here — at a 0.95 UEF, the top efficiency in this field. The difference-maker is ComfortFlow: a built-in recirculation pump and small buffer tank that kill the cold-water sandwich and the wait at distant taps, hardware the other brands sell as add-ons or skip entirely. Dual stainless heat exchangers, a 15:1 turndown that keeps low draws stable, and field conversion between natural gas and propane round it out. The honest catch is the channel: Navien is a wholesaler brand. Buy it through a licensed installer or distributor — marketplace units can carry warranty risk — and budget the install accordingly.
- ModelNPE-240A2
- Max input199,900 BTU/h
- Flow @ 70°F rise5.6 GPM
- UEF0.95
- Warranty15 yr exchanger · 5 yr parts · 1 yr labor
Rinnai Sensei RU199iN
86/100
Rinnai’s flagship indoor condensing unit, and the easiest premium tankless to buy through normal retail channels. The flow story is a lesson in reading curves: 9.8 GPM at a 35°F rise on the standard setting, 11 GPM with the parameter adjustment installers can unlock, and 5.5 GPM at a 70°F rise — within a tenth of the Navien. Efficiency trails slightly at 0.93 UEF. What puts it second overall is the support structure around it: the deepest dealer and parts network in tankless, Circ-Logic recirculation control built in (pump sold separately), and a labor warranty that stretches to five years if you register within 90 days — a detail buried in the warranty document that is worth real money. Register it.
- ModelRU199iN (Sensei)
- Max input199,000 BTU/h
- Flow @ 70°F rise5.5 GPM
- UEF0.93
- Warranty15 yr exchanger · 5 yr parts · labor to 5 yr*
Noritz EZ98DV
84/100
The EZ series exists for one job: replacing a tank without re-plumbing the room. Water connections sit on top of the cabinet, exactly where the old tank’s were, which is why installers quote these faster and cheaper than units that need the piping moved. The efficiency is the best in this field — 0.98 UEF on the current ENERGY STAR listing — and the warranty is the headline: 25 years on both stainless heat exchangers, a full decade past every other brand here, with 5 years on parts. What costs it points is winter flow: at 180,000 BTU/h it is the smallest burner in the gas group, and its flow curve gives back the difference — 4.9 GPM at a 70°F rise, roughly two showers with nothing left over. In a mild climate or a smaller house, that trade is invisible. In a cold one, it is the whole decision.
- ModelEZ98DV
- Max input180,000 BTU/h
- Flow @ 70°F rise4.9 GPM
- UEF0.98
- Warranty25 yr exchangers · 5 yr parts · 1 yr labor
Rheem RTGH-90DVLN-3
83/100
The strongest tankless you can buy at a normal retail counter, and the reference unit in our Tankless hub. Nine gallons a minute at a 35°F rise, 7.7 at 45°F, and 5.2 at the 67°F rise Rheem publishes — a hair behind the Navien and Rinnai at winter conditions, honestly reported. A 0.93 UEF matches the Rinnai, the 0.4 GPM activation flow is the joint-lowest here (fewer lukewarm hand-washes), and the warranty follows Rheem’s current RTGH document: 12 years on the heat exchanger for a single-family home, 5 on parts, 1 on labor. It lands fourth on channel math, not performance: no built-in recirculation pump, and a heat-exchanger term three years shorter than the leaders. For a self-managed install through retail, it is the straightforward pick.
- ModelRTGH-90DVLN-3
- Max input180,000 BTU/h
- Flow @ 67°F rise5.2 GPM
- UEF0.93
- Warranty12 yr exchanger · 5 yr parts · 1 yr labor
EcoSmart ECO 27
74/100
Electric tankless is a different sport, and this card scores it on its own field. The ECO 27 is the biggest residential electric unit in its class: 27 kW across three elements, self-modulating, 99.8% thermal efficiency at the element — and 3.1 GPM at a 70°F rise by EcoSmart’s own sizing table. That is one strong shower in a cold climate, two in a warm one. It also draws 112.5 amps on three dedicated 40-amp breakers, which means a 200-amp panel with real headroom, and EcoSmart’s limited lifetime warranty on electronics, exchanger and elements holds only with professional installation and timely registration — do not self-install this one and expect the warranty. Where gas is unavailable and demand is modest, it is a legitimate answer. As a like-for-like swap for a family-sized gas tank, it is not, and any page that tells you otherwise is selling something.
- ModelECO 27
- Power27 kW · 112.5 A · 3× 40A breakers
- Flow @ 70°F rise3.1 GPM
- Efficiency99.8% thermal (no UEF class)
- WarrantyLimited lifetime* — pro install + registration required
*Rinnai labor coverage is 5 years when the unit is registered within 90 days of installation, 1 year otherwise (Rinnai limited warranty document). EcoSmart’s limited lifetime covers the heater only — not labor — and requires professional installation plus timely registration (Amazon listing warranty text, checked 2026-11-09).
The deciding numbers, charted
One chart, one question: how much hot water does each unit actually make when winter groundwater hits it? This is the same 70°F rise the calculator sizes to.
Published flow at a 70°F temperature rise — Navien and Rinnai from their spec tables, Noritz from its flow table (interpolated between the 65°F and 75°F columns), EcoSmart from its sizing guide. Rheem publishes at 67°F; shown as published. Flow at your own rise will differ — that is the point of sizing first.
How the scoring works
Flow at winter rise (30) rewards what a unit delivers in January, not July. Efficiency (25) follows UEF for the gas units; the electric pick is scored on its own thermal efficiency and the panel cost it imposes. Running cost and upkeep (25) counts fuel math plus the annual descale every gas warranty quietly assumes — scale damage is excluded from coverage by all four gas brands, which is why the flush kit in the module below is not optional equipment. Warranty and parts (20) weighs exchanger term, parts term, labor — and whether the brand’s channel will actually honor a claim on a unit bought the way you bought it. The Navien wins on flow, efficiency and the built-in pump; it does not win by enough to survive a bad install, and neither does anything else on this page.
Why there are no prices on this page
Tankless pricing splits by channel harder than any other category we cover: the same Navien is one number at a wholesaler with an installer attached and another — with warranty questions attached — on a marketplace. Rather than print a number that is wrong by Friday, we print the numbers that do not move: flow at rise, UEF, warranty terms. What the full job should cost, installed, with the permit and the gas work itemized, lives on Water Heater Replacement Cost — read it before you read any quote.
Keep reading
From the desk
- 1Size your tankless first — the calculator that produces the GPM-at-rise number this page scores on
- 2What the install really costs — unit, labor, permit and code work, itemized
- 3Tankless vs tank — the five differences, if the tank question is still open
- 4Best tank water heaters — the flagship comparison, if a tank still wins your math
- 5Before you replace it — the failures that look fatal and are not