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Head-to-head · Best Tankless Water Heaters

Rheem RTEX-18 Electric Tankless Water Heater 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.

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The short answer

Rheem RTEX-18 Electric Tankless Water Heater is the only one of the two with a published score (4.5); Rinnai RU199iN has none, so this is not a close call so much as an unmeasured one. Rheem RTEX-18 Electric Tankless Water Heater is best for: small homes, apartments, additions or small buildings with modest hot-water demand and at least a 150A electrical panel. Read the strengths below before deciding.

Rheem RTEX-18 Electric Tankless Water Heater
Higher ratedRanked #1 in Best Tankless Water Heaters
Rheem RTEX-18 Electric Tankless Water Heater
1 source$427.9as of Oct 16

The Rheem RTEX-18 is an 18 kW, 240V electric tankless heater that Bob Vila's Glenda Taylor installed in a small commercial building and rated 4.8 out of 5. It mounts flat on a wall at 13.9 by 17 by 3.6 inches and delivered hot water at the sink within a few seconds. It is a small-capacity unit that needs two 40A double-pole breakers and a 150A service panel, so it suits light demand rather than a house with several bathrooms.

Strengths
  • — Compact 13.9 x 17 x 3.6 inch wall-mounted body, per Bob Vila
  • — Hot water reached the faucet in a few seconds in Bob Vila's installation
  • — Temperature set with a single front knob; Bob Vila settled on 120 degrees F
Watch-outs
  • — Requires a 150A service panel and two 40A double-pole breakers
  • — Small capacity: Bob Vila advises a higher-capacity model for a large home with several bathrooms
  • — Professional installation suggested; plumbing parts such as hoses and manifolds are bought separately
$427.9 · Check Price on AmazonFull review →
Rinnai RU199iN
Ranked #5 in Best Tankless Water Heaters
Rinnai RU199iN
Unrated3 sources

The Rinnai SENSEI RU199iN is an indoor natural-gas condensing tankless heater that Rinnai rates at 15,000 to 199,000 BTU, up to 11 GPM and a 0.95 Uniform Energy Factor. Rinnai lists it as recirculation capable, Wi-Fi capable and ENERGY STAR certified. No independent hands-on review of this exact model was found, so it is shown without a rating. It needs gas service and venting.

Strengths
  • — Rated up to 199,000 BTU and 11 GPM, per Rinnai
  • — 0.95 Uniform Energy Factor and ENERGY STAR certified, per Rinnai
  • — Recirculation capable and Wi-Fi capable, per Rinnai
Watch-outs
  • — Needs natural gas service and venting, so it is not an option for all-electric homes
  • — No independent hands-on review of this exact model was found
Buy at parksupplycompany.comFull review →

How they stack up

Rheem RTEX-18 Electric Tankless Water Heater

At up to 4.4 GPM in the warmest zone, per Bob Vila's spec table, the RTEX-18 is a smaller electric unit than the Stiebel Eltron Tempra 36 Plus (7.5 GPM) and well below the rated flow of the gas Rinnai RU199iN (11 GPM) and Takagi T-H3-DV-N (10 GPM). Unlike the gas units it needs no venting, but it does need two 40A double-pole breakers.

Rinnai RU199iN

At a rated 11 GPM it has the highest flow rating on the page, above the gas Takagi T-H3-DV-N (10 GPM) and the electric Stiebel Eltron Tempra 36 Plus (7.5 GPM), EcoSmart ECO 27 and Rheem RTEX-18. Unlike the three electric units it needs a gas supply and venting.

Specs side-by-side

SpecRheem RTEX-18 Electric Tankless Water HeaterRinnai RU199iN
Power18 kW—
Voltage240V—
Maximum Flow Rate4.4 GPM (warmest zone)—
Dimensions13.9 x 17 x 3.6 inches18.5"W x 30.11"H
Breaker SizeTwo 40A double-pole breakers—
Minimum Service Panel150 amps—
Water Temperature Range80 to 140 degrees F—
FuelElectricNatural gas
Flow Rate—Up to 11 GPM
BTU—15,000 - 199,000
Efficiency—0.95
Type—Condensing
Installation—Indoor
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