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Head-to-head · Best Tankless Water Heaters

Rheem RTEX-18 Electric Tankless Water Heater vs Takagi T-H3-DV-N

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 comes out ahead by a clear margin (4.5 vs 3.9). 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 →
Takagi T-H3-DV-N
Ranked #3 in Best Tankless Water Heaters
Takagi T-H3-DV-N
1 sourceall derived$1,500as of Jun 7

The Takagi T-H3-DV-N is Bob Vila's best condensing gas pick: a 10 GPM, 199,000 BTU unit built around a commercial-grade copper-alloy heat exchanger that suits heavier residential use like recirculation or space heating. It's Ultra-Low NOx compliant, which matters in strict-emission states, and Bob Vila praised that it 'provides plenty of heating power for most households.' Its 0.93 UEF trails the Rinnai RU199iN slightly and it lacks the Rinnai's smart-app polish. As a rugged, high-capacity condensing gas heater, it's an excellent whole-home choice.

Strengths
  • — Condensing gas design delivering up to 10 GPM
  • — 199,000 BTU handles most whole-home demand
  • — Ultra-Low NOx compliant for strict-emission regions like California
Watch-outs
  • — Requires gas service and condensing venting
$1,500 · Check Price on AmazonFull review →

Derived means the reviewer published no score, so one was inferred from their written verdict. Everything else is a number the publisher printed. How we rank.

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.

Takagi T-H3-DV-N

The Takagi T-H3-DV-N is the second gas unit here, matching much of the Rinnai RU199iN's 199,000 BTU output at a slightly lower 10 GPM and 0.93 UEF. Like the Rinnai it far outflows the electric Stiebel Eltron Tempra 36 Plus, EcoSmart ECO 27, and Rheem RTEX-13, but it offers fewer smart features than the Wi-Fi-equipped Rinnai.

Specs side-by-side

SpecRheem RTEX-18 Electric Tankless Water HeaterTakagi T-H3-DV-N
Power18 kW199,000 BTU/H
Voltage240V—
Maximum Flow Rate4.4 GPM (warmest zone)—
Dimensions13.9 x 17 x 3.6 inches17.75"W x 22.5"H
Breaker SizeTwo 40A double-pole breakers—
Minimum Service Panel150 amps—
Water Temperature Range80 to 140 degrees F—
FuelElectricNatural gas
Flow Rate—Up to 10 GPM
BTU—15,000 - 199,000
Efficiency—0.93
Type—Condensing, Ultra-Low NOx
Installation—Indoor, direct vent
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