EcoSmart vs Stiebel Eltron

Electric tankless is the category where the specification sheet decides everything and the marketing tells you nothing. Both of these units work. Whether either works in your house is a question about your electrical service, and only one of the two gives you the figures to answer it.

Side by side on published figures

The Stiebel row that most people miss is the 208 V one. Plenty of homes and nearly every apartment building sit nearer 208 V than 240 V, and at 208 V the Tempra 24 Plus drops from 24 kW to 18 kW — a quarter of its output, gone. Measure the voltage at the panel before you size anything.

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	Stiebel Eltron Tempra 24 PlusThe electric tankless to buy if you are going to buy one at all: it publishes its full rise-versus-flow curve, and the Advanced Flow Control throttles flow instead of letting the temperature sag.	Whole-house electric, warm inlet	Check price on Amazon No live price feed on this site, so we show none. #ad
2	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
3	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

The three units in full

Pick 1 — Whole-house electric, warm inlet

Stiebel Eltron Tempra 24 Plus

The electric tankless to buy if you are going to buy one at all: it publishes its full rise-versus-flow curve, and the Advanced Flow Control throttles flow instead of letting the temperature sag.

Published specifications for the Stiebel Eltron Tempra 24 Plus

Output at 240 V	24 kW
Output at 208 V	18 kW
Breakers	2 x 50 A double-pole
Wire	2 x 6 AWG copper
Current draw	100 A
Minimum electrical service	150 A
Rise at 240 V	54°F at 3.0 GPM; 73°F at 2.25 GPM; 37°F at 4.5 GPM
Rise at 208 V	41°F at 3.0 GPM; 54°F at 2.25 GPM; 27°F at 4.5 GPM
Maximum flow	8 GPM

What is good

• +Publishes rise at four flow rates on both voltages, which is the only honest way to size an electric tankless
• +Advanced Flow Control cuts flow to hold the set temperature rather than delivering lukewarm water
• +No venting, no gas line, no condensate
• +Small enough to go in the cabinet it replaced

What is not

• −100 A of draw and a 150 A minimum service rules out a lot of older houses
• −At 208 V it loses a quarter of its output, and plenty of homes are nearer 208 than 240
• −Running cost follows the electric rate, which is usually worse than gas per BTU

Skip it if: Skip it if your inlet water drops to 45°F in winter and you want two showers at once. At a 73°F rise it delivers 2.25 GPM — one shower, nothing else. Cold-inlet climates are where electric tankless disappoints people.

Check price on Amazon

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

Specifications above from Stiebel Eltron Tempra Plus technical specifications (PDF); Stiebel Eltron Tempra Plus submittal sheet (PDF). We have not tested this unit ourselves.

Pick 2 — 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 3 — 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.

Where Stiebel Eltron wins

• It publishes the curve. Rise at four flow rates on both voltages is the only honest way to size an electric tankless, and it is the reason this unit is our default pick in the category.
• Advanced Flow Control cuts flow to hold the set temperature instead of handing you lukewarm water at full flow. You get a slower shower rather than a cold one.
• 100 A of draw on a 150 A minimum service is the lowest barrier to entry of the three, which in older housing stock is frequently the deciding fact.
• Two circuits rather than three, which is two fewer breaker spaces to find.

Where EcoSmart wins

• 27 kW is the most output here, so it holds temperature at a higher flow rate than either 24 kW unit.
• A lifetime limited warranty on the unit is unusual at any price in this category.
• 0.3 GPM activation flow is the lowest on this page — a trickle still fires it.
• 3-5/8 inches deep and 14.7 pounds. It genuinely disappears on a wall where a tank could not go.

The honest case against both

Electric tankless disappoints people in cold-inlet climates, and the arithmetic is why. At a 73°F rise the Tempra 24 Plus delivers 2.25 GPM: one shower, nothing else running. If your groundwater drops to 45°F in winter and you want two showers at once, no single-unit electric tankless on the market will do it on a residential service. In that house the answer is a heat pump water heater or a gas tankless unit, not a bigger electric one.

What to buy