EcoSmart vs Rheem Electric Tankless

Electric tankless is the category where the brand argument is least important and the electrical argument is almost everything. The ECO 27 draws 113 A. The RTEX-24 is specified against a 200 A service. If your house has a 100 A or 125 A panel, the honest answer to this comparison is neither of them, and a service upgrade usually costs more than the water heater.

Side by side on published figures

Neither brand publishes a rise-qualified flow figure for its whole-house units, which is the same transparency failure the gas side has. The ECO 11 is the exception on this page: it states a flow range of 1.3 to 3.2 GPM and says openly that where you land inside it depends on inlet temperature. That is the correct way to quote an electric tankless unit, and it is why the smallest unit here is the most honest one.

Quick picks

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Ranked picks with what each one is best for, our score and a link to check the current price on Amazon.

#	Product	Best for	Price
1	EcoSmart ECO 27The biggest electric unit most homes can actually feed: 27 kW across three 40 A breakers, 6.6 GPM maximum, and a lifetime limited warranty on the unit.	Maximum electric output	Check price on Amazon No live price feed on this site, so we show none. #ad
2	Rheem Professional Classic RTEX-24The value electric unit: 24 kW, 5.9 GPM rated flow and a digital set point in 1°F steps, from a brand whose parts your local supply house actually stocks.	Electric tankless on a budget	Check price on Amazon No live price feed on this site, so we show none. #ad
3	EcoSmart ECO 11A single-fixture electric unit, not a whole-house one: 13.8 kW at 240 V delivering 1.3 to 3.2 GPM depending entirely on how cold your inlet water is.	One fixture, or a warm-inlet apartment	Check price on Amazon No live price feed on this site, so we show none. #ad

The three units in full

Pick 1 — Maximum electric output

EcoSmart ECO 27

The biggest electric unit most homes can actually feed: 27 kW across three 40 A breakers, 6.6 GPM maximum, and a lifetime limited warranty on the unit.

Published specifications for the EcoSmart ECO 27

Output	27 kW at 240 V, single phase
Current draw	113 A
Breakers	3 x 40 A
Wire	3 x 8 AWG
Maximum flow	6.6 GPM
Minimum activation flow	0.3 GPM
Dimensions	17 in x 17 in x 3-5/8 in
Weight	14.7 lb
Connections	3/4 in NPT
Warranty	Lifetime limited

What is good

• +Highest output of any single electric unit here, so it holds temperature at higher flow
• +Lifetime limited warranty on the unit is unusual at any price
• +3-5/8 inches deep — it genuinely disappears on a wall
• +0.3 GPM activation flow is the lowest on this page

What is not

• −113 A of draw needs three circuits and, in practice, a 200 A service
• −The published flow is a maximum, not a rise-qualified figure — you have to do the rise math yourself
• −No buffer, so a sudden flow change is felt at the shower head

Skip it if: Skip it if your panel is 100 A or 125 A. Three 40 A circuits and 113 A of draw is a service upgrade, and a service upgrade usually costs more than the entire water heater.

Check price on Amazon

No live price feed on this site, so we show none. #ad

Specifications above from EcoSmart ECO 27 technical data (BIMobject). We have not tested this unit ourselves.

Pick 2 — Electric tankless on a budget

Rheem Professional Classic RTEX-24

The value electric unit: 24 kW, 5.9 GPM rated flow and a digital set point in 1°F steps, from a brand whose parts your local supply house actually stocks.

Published specifications for the Rheem Professional Classic RTEX-24

Output	24 kW at 240 V
Rated flow	5.9 GPM
Breakers	3 x 40 A
Service required	200 A
Thermal efficiency	99.8%
Set point range	80 - 140°F in 1°F increments

What is good

• +Parts and warranty support through a brand with national distribution
• +Digital set point in single degrees rather than a notched dial
• +99.8% thermal efficiency: effectively all the electricity lands in the water
• +Cheaper than the German-built alternatives at the same kW

What is not

• −Rheem quotes a rated flow rather than a published rise-versus-flow curve
• −Three 40 A circuits and a 200 A service requirement
• −No flow control, so high flow shows up as lower temperature

Skip it if: Skip it if you want to size from published data. Rheem lists a rated GPM without the temperature rise it was measured at, so you cannot check the number against your own inlet temperature the way you can with the Tempra.

Check price on Amazon

No live price feed on this site, so we show none. #ad

Specifications above from Rheem RTEX-24 / RTEX-27 product page; Pace Supply listing, RTEX-24, 240 V 24 kW 100 A. We have not tested this unit ourselves.

Pick 3 — One fixture, or a warm-inlet apartment

EcoSmart ECO 11

A single-fixture electric unit, not a whole-house one: 13.8 kW at 240 V delivering 1.3 to 3.2 GPM depending entirely on how cold your inlet water is.

Published specifications for the EcoSmart ECO 11

Output	13.8 kW at 240 V; 11 kW at 220 V
Flow	1.3 - 3.2 GPM depending on inlet temperature
Breaker	60 A double-pole
Wire	6 AWG
Current draw	54 A
Energy factor	0.998
Set point	Digital, 1°F increments

What is good

• +One 60 A circuit instead of three, which many existing panels can take
• +Honest published flow range tied to inlet temperature
• +Small and light enough for a utility closet or under a counter
• +Good match for a single shower in a warm-inlet region

What is not

• −3.2 GPM is only reachable with warm inlet water
• −Still 54 A — not a plug-in appliance
• −No modulation headroom if a second fixture opens

Skip it if: Skip it as a whole-house heater anywhere north of the Sun Belt. At a northern winter inlet temperature it lands at the bottom of its range, which is a hand-wash flow rate, not a shower.

Check price on Amazon

No live price feed on this site, so we show none. #ad

Specifications above from EcoSmart ECO 6 / 8 / 11 specification sheet (PDF). We have not tested this unit ourselves.

Where EcoSmart wins

• 27 kW is the highest output here, and in electric tankless, kilowatts are capacity. Nothing else substitutes for them.
• A lifetime limited warranty on the unit, which no other electric tankless unit in our registry matches.
• A published 0.3 GPM minimum activation flow, the lowest on this page — it will fire for a trickle at a bathroom faucet.
• Published dimensions and weight, so you can plan the wall before the unit arrives: 17 by 17 by 3-5/8 inches and 14.7 pounds.
• The ECO 11 as a genuinely useful small unit for one fixture or a warm-inlet apartment, on a single 60 A double-pole breaker instead of three circuits.

Where Rheem wins

• Parts and service. Rheem is the brand whose components a local supply house stocks, and on an appliance that lives on three 40 A circuits, a part you can get the same day is worth something.
• A 1°F set point across 80 to 140°F, which is a more useful adjustment range than most units publish and matters if you are feeding a mixing valve.
• A published 99.8% thermal efficiency figure. All electric resistance heating is close to this by physics, but Rheem states it.
• One less kilowatt of demand than the ECO 27 at 24 kW, which can be the difference between a feasible retrofit and a service upgrade.
• The brand continuity argument — if the rest of the house is Rheem, one supplier handles the whole job.

The condition that flips it

What both brands get wrong

They quote flow without the temperature rise it was measured at. A maximum GPM on an electric tankless unit is an arithmetic ceiling: kilowatts divided by the rise you demand. The same ECO 27 that delivers 6.6 GPM in a Florida summer delivers a fraction of that at a Minnesota February inlet temperature, and the spec sheet does not say so. If you want the arithmetic rather than the marketing, the tankless sizing chart does it by rise, and the Stiebel Eltron Tempra is the one electric unit in our registry that publishes the full curve.

Pick EcoSmart if...

• You have the service for 113 A and want the most capacity available.
• A lifetime limited warranty on the unit matters to you.
• You need a small single-fixture unit on one circuit — that is the ECO 11.
• You want published dimensions and weight before you commit to a wall.

Pick Rheem if...

• You want parts and service you can get locally.
• A fine set point across 80 to 140°F is useful to you.
• One fewer kilowatt of demand helps the install.
• The rest of the house is already Rheem.