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Head-to-head · Best Tankless Water Heaters

EcoSmart ECO 27 vs Rheem RTEX-18 Electric Tankless Water Heater

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 3.7). 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.

EcoSmart ECO 27
Ranked #2 in Best Tankless Water Heaters
EcoSmart ECO 27
2 sourcesall derived

The EcoSmart ECO 27 is a 27 kW, 240V electric tankless heater that EcoSmart rates at a 113-amp draw on three dedicated 40A double-pole breakers, with digital temperature control in 1-degree steps from 80°F to 140°F. In a video review, TeslaMan, who installed one himself, found it kept a full house in hot water, but he had to upgrade his electrical service and replaced the heating elements three times in two years.

Strengths
  • — Kept a full house in hot water once running, in TeslaMan's video review
  • — Digital temperature control in 1-degree increments from 80°F to 140°F, per EcoSmart
  • — No gas line or venting
Watch-outs
  • — Needs three 40A double-pole breakers and a recommended 200A panel, per EcoSmart; TeslaMan had to upgrade his service
  • — TeslaMan replaced the heating elements three times in two years
  • — TeslaMan says the lifetime limited warranty requires installation by a licensed electrician, and appears not to cover the elements
Buy at homedepot.comFull review →
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 →

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

EcoSmart ECO 27

Its 27 kW sits between the 18 kW Rheem RTEX-18 and the 36 kW Stiebel Eltron Tempra 36 Plus, and it lacks the Advanced Flow Control that Stiebel Eltron says is exclusive to its Tempra Plus models. Like the other electric units it needs no gas line or venting, unlike the Rinnai RU199iN and Takagi T-H3-DV-N.

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.

Specs side-by-side

SpecEcoSmart ECO 27Rheem RTEX-18 Electric Tankless Water Heater
FuelElectricElectric
Flow Rate2.7 - 6.5 GPM (climate-dependent)—
Power27 kW18 kW
Efficiency99.8—
Dimensions17"W x 17"H13.9 x 17 x 3.6 inches
Voltage—240V
Maximum Flow Rate—4.4 GPM (warmest zone)
Breaker Size—Two 40A double-pole breakers
Minimum Service Panel—150 amps
Water Temperature Range—80 to 140 degrees F
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