Head-to-head · Best Tankless Water Heaters

Rinnai RU199iN vs Stiebel Eltron Tempra 36 Plus

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 (4.5 vs 4.4). 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.

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 →

Ranked #2 in Best Tankless Water Heaters

Stiebel Eltron Tempra 36 Plus

4.4

$789.11as of Jun 7

The Stiebel Eltron Tempra 36 Plus is the clear frontrunner for whole-home electric tankless heating, delivering up to 7.5 GPM from its 36 kW heating element. This Old House rated the Stiebel Eltron electric line 4.4/5, and Bob Vila named it best electric, both praising its silent operation and standout Advanced Flow Control, which dynamically reduces flow rather than letting cold-water sandwiching occur when demand exceeds capacity. It needs serious electrical service and performs best in moderate climates, but for an all-electric home it is the top whole-house pick.

Strengths

— Best whole-home electric option, up to 7.5 GPM at 36 kW
— Advanced Flow Control throttles flow to prevent cold-water sandwiching
— Silent operation with no combustion, venting, or CO risk

Watch-outs

— Needs substantial electrical service — often a panel upgrade
— Flow rate drops in cold climates with high temperature rise
— No federal gas tax credit (electric)

$789.11 · Check Price on Amazon Full review →

How they stack up

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.

Stiebel Eltron Tempra 36 Plus

The Stiebel Eltron Tempra 36 Plus is the best whole-home electric unit, with a 7.5 GPM flow rate that beats the EcoSmart ECO 27 and Rheem RTEX-13 but trails the gas Rinnai RU199iN and Takagi T-H3-DV-N. Its Advanced Flow Control is a feature neither the EcoSmart nor the Rheem offers, trading a brief flow reduction for consistently hot water.

Specs side-by-side

Spec	Rinnai RU199iN	Stiebel Eltron Tempra 36 Plus
Fuel	Natural gas	Electric
Type	Condensing	—
Flow Rate	Up to 11 GPM	Up to 7.5 GPM
BTU	15,000 - 199,000	—
UEF	0.95	—
Connectivity	Wi-Fi (Rinnai app)	—
Installation	Indoor	—
Tax Credit	Qualifies (UEF 0.95+)	—
Power	—	36 kW
Control	—	Advanced Flow Control + self-modulating
Voltage	—	240/208V
Venting	—	None required
Mounting	—	Wall-mounted
Origin	—	Made in Germany

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