Head-to-head · Best Tankless Water Heaters

EcoSmart ECO 27 vs Rinnai RU199iN

Which is the better buy? Side-by-side on rating, price, strengths, and watch-outs — with the published ratings we averaged to get there.

The short answer

Rinnai RU199iN comes out ahead by a narrow margin (4.2 vs 4.5). The gap is mostly about Large households with gas service that need whole-home hot water for multiple bathrooms at once. — read the strengths below before deciding.

Ranked #4 in Best Tankless Water Heaters

EcoSmart ECO 27

4.2

$466.24as of Jun 7

The EcoSmart ECO 27 is the efficient electric value pick — a 27 kW self-modulating unit that This Old House rated 4.3/5 for the EcoSmart line, praising that it 'can save you up to 50% on your water-heating bill thanks to its self-modulating temperature control.' It delivers up to 6.5 GPM in warm climates, enough for a small whole home, from a compact wall-mounted box with precise digital temperature control. Its flow drops in cold-inlet regions and it needs substantial electrical service, but for warm-climate homes it's a strong, affordable electric option.

Strengths

— Self-modulating technology uses only the energy needed
— Up to 6.5 GPM in warm climates, enough for small whole-home use
— Compact 17 x 17 x 3.5-inch wall-mounted footprint

Watch-outs

— Flow rate drops sharply in cold-inlet climates (down to ~2.7 GPM)
— 27 kW draw requires significant electrical service
— Best suited to warm regions or smaller homes

$466.24 · Check Price on Amazon Full review →

Higher ratedRanked #1 in Best Tankless Water Heaters

Rinnai RU199iN

4.5

$1,177.78as of Jun 7

The Rinnai RU199iN is the best overall gas tankless water heater for whole-home use, delivering up to 11 GPM and 199,000 BTU — enough hot water for up to five appliances or a 3-4 bathroom house running simultaneously. Bob Vila named the Rinnai SENSEI line its best overall, and reviewers consistently praise the condensing efficiency (0.95 UEF, which qualifies for the federal tax credit) and Wi-Fi control. It is the priciest pick and needs gas service and condensing venting, but for a busy household in any climate, nothing here matches its capacity.

Strengths

— Industry-leading 11 GPM flow rate handles a 3-4 bathroom home at once
— Condensing design with a 0.95 UEF qualifies for the 30% federal tax credit
— 199,000 BTU output keeps up even in cold inlet climates

Watch-outs

— Highest upfront and installation cost of the group
— Requires gas service and proper condensing venting
— Overkill for a small home or apartment

$1,177.78 · Check Price on Amazon Full review →

How they stack up

EcoSmart ECO 27

The EcoSmart ECO 27 is the mid-tier electric option, more affordable than the whole-home Stiebel Eltron Tempra 36 Plus but with lower and more climate-dependent flow (2.7-6.5 GPM). It lacks the Stiebel's Advanced Flow Control. It outflows the point-of-use Rheem RTEX-13 but, like all electric units here, trails the gas Rinnai RU199iN and Takagi T-H3-DV-N.

Rinnai RU199iN

The Rinnai RU199iN is the highest-capacity unit here, with an 11 GPM gas flow rate that dwarfs the electric Stiebel Eltron Tempra 36 Plus (7.5 GPM), EcoSmart ECO 27, and Rheem RTEX-13. Only the gas Takagi T-H3-DV-N approaches it, and the RU199iN edges it on UEF efficiency. It costs the most upfront and, unlike the electric units, requires gas and condensing venting.

Specs side-by-side

Spec	EcoSmart ECO 27	Rinnai RU199iN
Fuel	Electric	Natural gas
Power	27 kW	—
Flow Rate	2.7 - 6.5 GPM (climate-dependent)	Up to 11 GPM
Control	Self-modulating, digital (1-degree)	—
Dimensions	17 x 17 x 3.5 in	—
Venting	None required	—
Mounting	Wall-mounted	—
Best Climate	Warm / southern U.S.	—
Type	—	Condensing
BTU	—	15,000 - 199,000
UEF	—	0.95
Connectivity	—	Wi-Fi (Rinnai app)
Installation	—	Indoor
Tax Credit	—	Qualifies (UEF 0.95+)

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