For most homes with 150 A service, get the Stiebel Eltron Tempra 24 Trend: 24 kW on two 50 A breakers, 0.97 UEF and a 7-year leak warranty. Cold winter water and 300 A service? The EcoSmart ECO 36 makes the most hot water here, 3.6 GPM from 37°F water. For one sink, the ECO 11 runs on a single 60 A breaker.
Most homes on 150 A service: Tempra 24 Trend$514.23 at AmazonPrice as of Oct 23, 2026, 5:30 AM EDT
All four were new, in stock and the buy-box offer at our 10:58 AM check on Oct 21. Amazon.com sells the two Stiebel units. The two EcoSmart units come from third-party sellers, listed under brand EcoSmart with the exact model number.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How much hot water each one makes
An electric tankless heater’s output depends on how cold the water comes in. Both makers publish the same physics, so the four heaters line up bar for bar at each incoming temperature.
Gallons per minute at a 105°F setting. EcoSmart figures are from its ECO 18–36 and ECO 8/11 spec sheets (2024). Stiebel figures are our arithmetic from its kW ratings (kW × 6.824 ÷ rise), which matches Stiebel’s own rise table within 1°F. Shower lines use EcoSmart’s 2 GPM per shower.
Read the bar for your incoming water. In a 37°F winter, the ECO 36 makes 3.6 GPM, close to two 2 GPM showers. The Tempra 24 makes 2.4 GPM there, one shower, and the Tempra 20 makes 1.9.
Warm the incoming water and every bar grows. From 67°F water the ECO 36 makes 6.5 GPM, enough for three showers, and the Tempra 24 makes 4.3, enough for two.
The arithmetic is the same for both brands: kilowatts × 6.824 ÷ temperature rise gives gallons per minute. EcoSmart’s zone table follows it to the tenth. Stiebel lists a 73°F rise at 2.25 GPM for the 24 kW Tempra, and the formula gives 72.8°F.
That means brand doesn’t change flow at a given kW. A 24 kW EcoSmart and a 24 kW Stiebel make the same hot water. The differences are breakers, efficiency, size and warranty.
Whole-house heaters, matched by panel size
Best for 150 A homes: 24 kW on two 50 A breakers
Stiebel Tempra 24 Trend
Stiebel Eltron Tempra 24 Trend electric tankless water heater
Sold by Amazon.com · in stock · price as of Oct 23, 2026, 5:30 AM EDT
Prices and availability are accurate as of the time shown and may change.
Pros
24 kW on two 50 A breakers, one fewer than the ECO 24
0.97 UEF, against 0.93 for EcoSmart’s ECO 24
7-year leak and 3-year parts warranty from purchase
Capacity bar, Tmax limit and display lock
Sold by Amazon.com
Cons
2.4 GPM from 37°F water: one shower in a cold winter
Stiebel recommends 150 A main service
No flow readout; that’s the Tempra 24 Plus
3-year parts term, against EcoSmart’s lifetime ECO terms
24 kW at 240 V2 × 50 A breakers2 runs 8/2 AWG0.97 UEF16.1 lb¾ in. NPT
Buy it if
Your home has 150 A or larger service with room for two 50 A double-pole breakers, and your incoming water runs about 52°F or warmer most of the year. From 52°F water it makes about 3.1 GPM at a 105°F setting.
Skip it if
Your winter water comes in near 37°F and you need two showers at once. The EcoSmart ECO 36 makes 3.6 GPM from 37°F water, if your service is 300 A.
The Tempra 24 Trend is the 24 kW Stiebel Eltron electric tankless water heater, item number 239216. Amazon.com sold it new and in stock at our 10:58 AM check on Oct 21. Its closest EcoSmart rival is the ECO 24, also 24 kW.
The wiring is where they split. Stiebel runs the Tempra 24 on two 50 A double-pole breakers with two runs of 8/2 copper. EcoSmart runs the ECO 24 on three 40 A breakers and three 8 AWG runs. One fewer breaker can decide whether a crowded panel takes the heater at all.
Stiebel recommends at least 150 A main service for the Tempra 24, depending on the rest of the house’s load. EcoSmart recommends 200 A for its ECO 24. Both are recommendations, so your electrician’s load calculation is what actually decides.
Flow follows the 24 kW rating. At a 105°F setting it makes about 2.4 GPM from 37°F water, 3.1 from 52°F and 4.3 from 67°F. That’s our arithmetic from Stiebel’s rating, and it matches Stiebel’s own table: a 73°F rise at 2.25 GPM.
Stiebel rates it 0.97 UEF, against 0.93 for the ECO 24. The case is 16⅝ in. wide, 14½ in. tall and 4⅝ in. deep, and weighs 16.1 lb. Connections are ¾ in. NPT, and Stiebel’s manual calls for detachable connectors, such as braided steel flex connectors.
The Trend display shows the set temperature and a bar for how hard the heater is working. A Tmax setting caps the top temperature, and a display lock stops anyone changing it. The Tempra 24 Plus adds a flow readout, a running savings estimate and two preset buttons.
The warranty is 7 years against leaks and 3 years against failed parts, both from the purchase date. Stiebel’s manual says to register within 90 days of purchase on its website to activate it. Hard water, freezing and moving the heater are excluded.
My call: this is the pick for most homes that can take it. It does the ECO 24’s job on fewer breakers, with higher efficiency, sold by Amazon.com itself. Check your winter water temperature first: below about 65°F incoming, it runs one shower plus a faucet, not two showers.
Best for cold inlet water: 3.6 GPM from 37°F water
Sold by SpaceCityProviders · in stock · price as of Oct 23, 2026, 5:30 AM EDT
Prices and availability are accurate as of the time shown and may change.
Pros
Most flow here: 3.6 GPM from 37°F water, 6.5 from 67°F
Limited lifetime warranty on the US mainland and in Canada
Copper heat exchanger, four chambers
Only 3⅝ in. deep
Set in 1° steps from 80 to 140°F
Cons
Four 40 A breakers and 150 A of draw
EcoSmart recommends 300 A service
Warranty needs licensed installers and registration within 30 days
Sold by a third-party seller, not Amazon.com
36 kW at 240 V4 × 40 A breakers4 runs 8 AWG0.94 UEF18.35 lb¾ in. NPT
Buy it if
Your incoming water is cold in winter, you want two showers at once, and your home has 300 A service, the size EcoSmart recommends, with room for four 40 A breakers.
Skip it if
Your home has 150 A service. The Tempra 24 Trend fits Stiebel’s 150 A recommendation on two 50 A breakers, at about 2.4 GPM from 37°F water.
The ECO 36 is EcoSmart’s largest whole-house electric heater, rated 36 kW at 240 V. It was new and in stock from SpaceCityProviders, a third-party seller, at our 10:58 AM check on Oct 21. The listing names brand EcoSmart and model ECO 36. It’s the biggest heater on this page by a wide margin.
It’s built from four 9 kW elements in four chambers, each on its own 40 A double-pole breaker and 8 AWG run. Total draw is 150 A. EcoSmart recommends 300 A household service for it, and warns that switching from an electric tank often needs a panel upgrade.
That power buys flow. EcoSmart’s zone table, figured to a 105°F setting, lists 3.6 GPM from 37°F water, 4.6 from 52°F, 6.5 from 67°F and 8.8 from 77°F. From 37°F water it makes more than the Tempra 24 makes from 52°F.
Stiebel’s size match is the Tempra 36: 36 kW on three 50 A breakers, with the same 300 A service recommendation. It rates 0.98 UEF against the ECO 36’s 0.94, and weighs 19.0 lb against 18.35. Flow is the same, because the kW is the same.
The case is 17 in. tall, 21 in. wide and only 3⅝ in. deep, with brass ¾ in. NPT fittings on the bottom. EcoSmart’s manual asks for 12 in. of clearance above and below, 6 in. in front and at the sides, and 24 in. from anything combustible.
The warranty is the strongest on paper: limited lifetime on the US mainland and in Canada, 5 years elsewhere. The conditions are strict. A licensed electrician and plumber must install it within 30 days of receipt, with proof, and you must register within 30 days or the warranty is void.
Scale, sediment, chlorine corrosion, freezing and failing to purge air are excluded. EcoSmart’s manual says to bleed the air from the lines before the power goes on, or the elements can be damaged for good. Labor isn’t covered.
My call: the ECO 36 is the answer for cold water and big demand, if the panel is there. Book the electrician before the heater ships, because the 30-day install clock starts when it arrives.
Best for 125 A service: 19.2 kW on two 40 A breakers
Stiebel Tempra 20 Trend
Stiebel Eltron Tempra 20 Trend electric tankless water heater
Sold by Amazon.com · in stock · price as of Oct 23, 2026, 5:30 AM EDT
Prices and availability are accurate as of the time shown and may change.
Pros
Stiebel recommends 125 A service, lowest of the whole-house picks
Two 40 A breakers, like EcoSmart’s ECO 18
0.97 UEF
7-year leak, 3-year parts warranty
Sold by Amazon.com
Cons
1.9 GPM from 37°F water, under one 2 GPM shower
4.7 GPM even from 77°F water
No flow readout on the Trend
Same case and weight as the Tempra 24
19.2 kW at 240 V2 × 40 A breakers2 runs 8/2 AWG0.97 UEF16.1 lb¾ in. NPT
Buy it if
Your home has 125 A service, your incoming water stays near 60°F or warmer, and one shower at a time is your peak.
Skip it if
Your water comes in cold. From 37°F water it makes about 1.9 GPM at 105°F, so step up to the Tempra 24 Trend if your panel allows two 50 A breakers.
The Tempra 20 Trend is Stiebel Eltron’s 19.2 kW model, item number 239215. Amazon.com sold it new and in stock at our 10:58 AM check on Oct 21. EcoSmart’s nearest size is the ECO 18, at 18 kW on the same two 40 A breakers.
Stiebel recommends 125 A main service for it, against 150 A for the Tempra 24. EcoSmart recommends 150 A for the ECO 18. For an older house with a smaller panel, that lower number is the reason to look here first.
Draw is two legs of 40 A, 80 A total, on two runs of 8/2 copper. Stiebel’s spec sheet asks for copper conductors rated 75°C or higher, sized to keep voltage drop under 3% at full load.
Flow is the trade. At a 105°F setting, 19.2 kW makes about 1.9 GPM from 37°F water, 2.5 from 52°F, 3.4 from 67°F and 4.7 from 77°F. Stiebel’s own table lists a 58°F rise at 2.25 GPM. EcoSmart lists 1.8 GPM from 37°F water for its ECO 18.
EcoSmart’s fixture table puts a shower at 2 GPM and a low-flow shower at 1.5. From 37°F water, the Tempra 20’s 1.9 GPM covers the low-flow head but not the standard one. In a warm climate it runs a shower and a faucet together.
It shares the Tempra 24’s case: 16⅝ by 14½ by 4⅝ in., 16.1 lb, ¾ in. NPT, and 0.50 GPM to switch on. Stiebel lists 131°F as the hottest water it may be fed. The display, Tmax limit and lock match the Tempra 24.
Warranty terms match too: 7 years on leaks and 3 on parts from purchase, with registration within 90 days. Stiebel’s manual says to install it where a leak won’t damage the area, or to fit a drain pan where that can’t be avoided.
My call: buy it when the panel decides, not the climate. If you have 150 A service and room for two 50 A breakers, the Tempra 24 adds 25% more flow in the same box for the same install work.
Sold by The Factory Depot · in stock · price as of Oct 23, 2026, 5:30 AM EDT
Prices and availability are accurate as of the time shown and may change.
Pros
One 60 A double-pole breaker and one 6 AWG run
EcoSmart recommends 100 A service
6.5 lb, 11.4 × 7.9 × 3.7 in.
Same limited lifetime ECO warranty
Turns on at 0.3 GPM
Cons
1.3 GPM from 37°F water: a sink, not a shower
0.92 UEF, lowest here
Same 30-day install and registration rules
Sold by a third-party seller
13 kW at 240 V1 × 60 A breaker1 run 6 AWG0.92 UEF6.5 lb½ in. compression
Buy it if
You want instant hot water at one far sink or a small bathroom, and you can run one 60 A, 240 V circuit to it.
Skip it if
You want a whole-house heater. Even from 77°F water it makes 3.2 GPM. Look at the Tempra 20 Trend or larger.
The ECO 11 is EcoSmart’s point-of-use heater. Despite the name, it’s rated 13 kW at 240 V, from two 6.5 kW elements. It was new and in stock from The Factory Depot, a third-party seller, at our 10:58 AM check on Oct 21, listed under brand EcoSmart and model ECO 11.
It needs one 60 A double-pole breaker and one 6 AWG run, with 54 A of draw. EcoSmart recommends 100 A service. That’s the smallest electrical job on this page, and the only pick that runs on a single circuit.
Stiebel’s nearest model is the Tempra 12 Trend: 12 kW on one 50 A breaker with 8/2 wire, and Stiebel also recommends 100 A service. It’s a much bigger box, 16⅝ by 14½ in. and 13.5 lb, and rates 0.94 UEF against the ECO 11’s 0.92.
EcoSmart’s zone table lists 1.3 GPM from 37°F water at a 105°F setting, 1.7 from 52°F, 2.3 from 67°F and 3.2 from 77°F. Its spec sheet calls it right for a low-flow faucet or bathroom faucet, and says it can run a shower in warmer climates.
It’s small: 11.4 by 7.9 by 3.7 in. and 6.5 lb, in a polymer shell with a stainless steel heat exchanger. The ½ in. compression fittings sit on the sides, not the bottom, so plan the supply lines before you pick the spot under the sink.
It switches on at 0.3 GPM and holds a setting from 80 to 140°F in 1° steps. Mounted at the sink, it cuts the wait for hot water at that one tap, which is the whole point of a point-of-use heater.
The ECO lifetime warranty applies, with the same strings: a licensed electrician and plumber, install within 30 days of receipt and registration within 30 days. EcoSmart’s manual also wants a drained catch pan where a leak could cause damage.
My call: pick it for one sink or a powder room, not a whole house. Our EcoSmart ECO 11 review covers it in more depth, including where it fits under a vanity.
The four linked heaters side by side
Scroll sideways on a phone; tap a heading on desktop to sort.
GPM at a 105°F setting. EcoSmart flow is from its zone tables; Stiebel flow is our arithmetic from its kW rating, checked against its rise table.
Which model your electrical panel can carry
Electric tankless heaters draw more current than anything else in most houses. Each maker publishes a minimum main service for every model. Here they are side by side.
Main service
Stiebel Eltron Tempra
EcoSmart ECO
100 A
Tempra 12 (1 × 50 A) or Tempra 15 (2 × 30 A)
ECO 8 (1 × 40 A) or ECO 11 (1 × 60 A)
125 A
Tempra 20 (2 × 40 A)
No model listed at 125 A
150 A
Tempra 24 (2 × 50 A)
ECO 18 (2 × 40 A)
200 A
Tempra 29 (3 × 40 A)
ECO 24 or ECO 27 (3 × 40 A)
300 A
Tempra 36 (3 × 50 A)
ECO 36 (4 × 40 A)
At the same service size, Stiebel lists more heater. On 150 A, Stiebel recommends its 24 kW Tempra 24; EcoSmart’s 150 A model is the 18 kW ECO 18. On 200 A, Stiebel’s Tempra 29 is 28.8 kW against EcoSmart’s 27 kW ECO 27.
These are each maker’s minimums, not a guarantee. Stiebel’s footnote says it depends on the total electric load at the house. EcoSmart puts the job of confirming power on the buyer, in writing, in its warranty.
Ask your electrician for a load calculation before you order. Bring the heater’s total amps: 100 A for the Tempra 24, 150 A for the ECO 36. An electric range, dryer, heat pump and car charger all count against the same service.
Every Tempra and ECO model, wired and rated
Scroll sideways on a phone. Both lines run on 240 V, single phase. Figures are from each maker’s current spec sheet.
Model
kW
Total amps
Breakers
Wire
UEF
Weight
Stiebel Tempra 12
12
50
1 × 50 A
1 × 8/2 AWG
0.94
13.5 lb
Stiebel Tempra 15
14.4
60
2 × 30 A
2 × 10/2 AWG
0.96
16.1 lb
Stiebel Tempra 20
19.2
80
2 × 40 A
2 × 8/2 AWG
0.97
16.1 lb
Stiebel Tempra 24
24
100
2 × 50 A
2 × 8/2 AWG
0.97
16.1 lb
Stiebel Tempra 29
28.8
120
3 × 40 A
3 × 8/2 AWG
0.98
19.0 lb
Stiebel Tempra 36
36
150
3 × 50 A
3 × 8/2 AWG
0.98
19.0 lb
EcoSmart ECO 8
8
33
1 × 40 A
1 × 8 AWG
0.96
4.75 lb
EcoSmart ECO 11
13
54
1 × 60 A
1 × 6 AWG
0.92
6.5 lb
EcoSmart ECO 18
18
75
2 × 40 A
2 × 8 AWG
0.94
11.7 lb
EcoSmart ECO 24
24
100
3 × 40 A
3 × 8 AWG
0.93
14.25 lb
EcoSmart ECO 27
27
112.5
3 × 40 A
3 × 8 AWG
0.93
14.7 lb
EcoSmart ECO 36
36
150
4 × 40 A
4 × 8 AWG
0.94
18.35 lb
Stiebel’s total amps are the sum of its per-circuit draw: two legs of 50 A on the Tempra 24, for example. EcoSmart lists totals directly. Stiebel sizes breakers at 100% of load and calls a tankless heater a non-continuous load, per its spec sheet footnote.
Efficiency runs higher on the Stiebel side: 0.97 to 0.98 UEF on the whole-house Tempras, 0.93 to 0.94 on the whole-house ECOs. On an electric heater with no flue, those numbers are all high, and the gap is a few cents on the dollar.
Tempra 24 Trend against ECO 24, check by check
Same 24 kW, so the same hot water. Everything else differs. Scroll sideways on a phone.
Check
Stiebel Tempra 24 Trend
EcoSmart ECO 24
Ahead
Power
24 kW
24 kW
Even
GPM from 37°F water at 105°F
2.4
2.4
Even
Breakers
2 × 50 A
3 × 40 A
Stiebel
Wire runs
2 × 8/2 AWG
3 × 8 AWG
Stiebel
Recommended main service
150 A
200 A
Stiebel
Efficiency (UEF)
0.97
0.93
Stiebel
Size (W × H × D)
16⅝ × 14½ × 4⅝ in.
17 × 17 × 3⅝ in.
Even
Weight
16.1 lb
14.25 lb
EcoSmart
Turn-on flow
0.50 GPM
0.3 GPM
EcoSmart
Temperature range
68–140°F
80–140°F
Stiebel
Water pressure
30–150 psi
25–150 psi
Even
Warranty
7 yr leak, 3 yr parts
Limited lifetime
EcoSmart
Warranty conditions
Licensed installers; register in 90 days
Licensed installers; install and register within 30 days
Stiebel
New and in stock on Amazon today
Yes, Amazon.com
Not on our shortlist
Stiebel
“Ahead” means ahead on that one check, not overall. The ECO 24 didn’t come up as a new, in-stock listing in our Oct 21 search, so it isn’t linked.
Three warranties, and what voids each one
EcoSmart sells two lines with two very different warranties, and the ECO line has the longer one. Stiebel’s is shorter on paper and easier to keep.
EcoSmart ECO
EcoSmart ECOS
Stiebel Tempra
Term
Limited lifetime (US mainland, Canada); 5 yr elsewhere
5 yr leak, 1 yr parts
7 yr leak, 3 yr parts
Clock starts
Installation date
Purchase date, or new-home occupancy for leaks
Purchase date
Registration
Within 30 days of receipt, or void
Within 30 days, or void
Within 90 days of purchase
Who installs
Licensed electrician and plumber, within 30 days of receipt, with proof
Licensed electrician and plumber, per code
Licensed electrician and plumber, per code; no install deadline
Labor
Not covered
Not covered
Not covered
Scale and hard water
Excluded
Not stated as a separate exclusion
Excluded
Freezing
Excluded
Excluded
Excluded
Air not purged (dry fire)
Excluded
Excluded
Not stated as a separate exclusion
Heater moved
Covers the original address
Excluded
Excluded
The ECO lifetime term is real, but it’s conditional. EcoSmart’s text says the heater must be installed within 30 days of receipt by a licensed electrician and plumber, and that warranties are void without registration within 30 days. In new construction, it asks you to tell it in advance if installation will be later.
The ECOS line carries 5 years on leaks and 1 year on parts. Its manual also makes registration within 30 days a condition.
Stiebel’s manual also calls for a licensed electrician and plumber, but its warranty sets no install deadline. Its one deadline is 90 days to register online, and coverage runs from the purchase date. If you can’t show a purchase date, it runs from the date of manufacture stamped on the heater.
Whichever you buy, keep the receipt, the installer’s invoice and the registration confirmation together. All three warranties exclude freezing and leave labor to you.
ECO or ECOS: two EcoSmart lines
EcoSmart’s current sizes come in two lines: ECO 8 to ECO 36, and ECOS 12, 18 and 27. The names are a letter apart, and the warranties are years apart.
ECO line
ECOS line
Sizes
8, 11, 18, 24, 27 and 36 kW
12, 18 and 27 kW
Warranty
Limited lifetime, conditional
5 yr leak, 1 yr parts
Registration
30 days
30 days
Amazon stock, Oct 21
ECO 8, ECO 11 and ECO 36 in stock
ECOS 18: only 5 left; ECOS 27: future date; ECOS 12: only 1 left
The earlier version of this page linked the ECOS 18 and ECOS 27. Neither passes our stock rule today: we skip listings that show only a few units left or only a future ship date, because the link may be dead by the time you click.
If you find an ECOS model in stock, read its warranty card before you compare it with a Tempra. A 1-year parts term is shorter than Stiebel’s 3 years.
Which Tempra display version you need
Every Tempra size comes as a Trend and a Plus. The elements, wiring and warranty match at each size; the display and one valve don’t.
Feature
Tempra Trend
Tempra Plus
Digital temperature display and dial
Yes
Yes
Capacity bar
Yes
Yes
Tmax top-temperature limit
Yes
Yes
Display lock
Yes
Yes
Flow readout in GPM
No
Yes
Running cost-savings estimate
No
Yes
Two preset buttons
No
Yes
Advanced Flow Control motorized valve
No
Yes
kW, breakers, wire, warranty
Same by size
Same by size
The Plus is worth it if you want to see how much water you’re pulling, which helps when a shower runs cool and you suspect the flow. Stiebel’s spare-parts list also shows its Advanced Flow Control technology, a motorized valve, on every Plus and none on the Trend.
On a Trend, when demand passes capacity, the manual has you turn the flow down by hand until the power light stops blinking. Otherwise, the Trend heats the same water on the same breakers. Stiebel item numbers make it easy to tell apart: 239216 is the Tempra 24 Trend and 239222 is the Tempra 24 Plus.
Installation rules from each manual
Both are wall-hung, unvented and wired to 240 V. Their manuals differ on clearances, connectors and relief valves. Scroll sideways on a phone.
Rule
Stiebel Tempra
EcoSmart ECO
Mounting
Vertical, water connections at the bottom
Upright; bottom fittings (ECO 18–36), side fittings (ECO 8, 11)
Clearance
5 in. on all sides
12 in. above and below, 6 in. front and sides; combustibles 24 in. away
Water pressure
30–150 psi; pressure-reducing valve above 150
25–150 psi; pressure-reducing valve above 150
Relief valve
Not required unless the inspector requires it
Not required by UL 499; Massachusetts and Kentucky require one
Connectors
Detachable connectors, such as braided steel flex connectors
Flexible connectors recommended; ball valves on inlet and outlet
Leak protection
Drain pan where a leak could damage the area
Drained catch pan where a leak could cause damage
Freezing
Not where it can drop below 36°F
Not where it can freeze
Before power on
Purge air from the heater
Purge air from the lines; skipping it can damage the elements
The air purge matters most. Both manuals say to run water through the heater until the air is out before the breakers go on. A tankless element fired with no water around it can burn out, and EcoSmart’s warranty excludes that damage.
EcoSmart also says not to solder pipes with the heater connected, and that pipes within 3 ft of it should be rated for 150°F. Our water heater drain pan guide covers pan sizes and drains.
On 208 V, both lose a quarter
Apartments, condos and some commercial buildings have 208 V instead of 240 V. Both makers allow it, and both lose the same share of heat.
Model
At 240 V
At 208 V
Stiebel Tempra 12
12 kW
9 kW
Stiebel Tempra 20
19.2 kW
14.4 kW
Stiebel Tempra 24
24 kW
18 kW
Stiebel Tempra 36
36 kW
27 kW
EcoSmart ECO models
Rated kW
75% of rated kW, after a jumper change
Stiebel lists 208 V output in its spec sheet. EcoSmart says to change a jumper setting on the control board for 208 V, and that output drops to 75%. Either way, size up one model if your building is 208 V. Our 240 V vs 208 V guide explains why the drop is a quarter.
When either one won’t heat: what the manuals say
Most “not hot enough” calls on an electric tankless heater come down to flow, voltage or scale. Here is each maker’s own troubleshooting list.
Symptom
Stiebel Tempra says
EcoSmart ECO says
No hot water at all
Breakers off; flow too low to switch on: clean the filter screen and aerator; flow sensor clogged; inlet and outlet reversed
Breakers off or wiring wrong; flow under the 0.3 GPM switch-on rate
Lukewarm at high flow
Flow too high: reduce it until the power light stops blinking
Flow beyond capacity: add an EcoSmart flow regulator (ECO IFR 1-2 or 3-4)
Lukewarm all the time
Voltage too low
Setting too low; voltage under 240 V; crossed wires on a new install; too much cold mixed in at the tap
Stopped heating
Safety thermal cutout tripped: power off and reset it
Display lit but no heat: internal part failure; call EcoSmart support
Weak hot water flow
Filter screen clogged; scale on the elements: descale them
Hard water: EcoSmart says to maintain more often
Stiebel’s thermal cutout is the answer to most “how do I reset a Stiebel Eltron tankless” questions: turn off the breakers, then reset the cutout as its manual describes. If it trips again, the cause is still there. For scale, see our tankless descaling guide.
Recall check for both brands
Brand
Recalls found on cpsc.gov
Covers these models?
EcoSmart
None found
No
Stiebel Eltron
None found
No
Searched the CPSC recall database by brand on Oct 21, 2026, at 10:54 AM. The same search for another water heater brand returned its recalls, so the database was answering.
How to choose in four questions
150 A service, mild water
Stiebel Tempra 24 Trend: two 50 A breakers, about 3.1 GPM from 52°F water at 105°F.
300 A service, cold water
EcoSmart ECO 36: four 40 A breakers, 3.6 GPM from 37°F water and 6.5 from 67°F.
125 A service
Stiebel Tempra 20 Trend: two 40 A breakers. Plan on one shower at a time in winter.
One sink far from the tank
EcoSmart ECO 11: one 60 A circuit, 1.3 to 3.2 GPM depending on the water.
Under 125 A, or a full panel
Get a load calculation first. A whole-house electric tankless heater may need a service upgrade.
Question
If yes
If no
Is your main service 300 A?
ECO 36 for the most flow, or a Tempra 36
Keep going
Is it 150 A or more, with room for two 50 A breakers?
Tempra 24 Trend
Keep going
Is it 125 A, with room for two 40 A breakers?
Tempra 20 Trend, if one shower at a time is enough
Keep going
Do you only need one sink?
ECO 11 on one 60 A circuit
Talk to an electrician about service size before buying any whole-house unit
At the same kW they make the same hot water. Stiebel’s Tempra runs fewer breakers at each size, rates higher efficiency (0.97 to 0.98 UEF against 0.93 to 0.94) and gives you 90 days to register instead of 30. EcoSmart’s ECO line has the longer warranty term, limited lifetime, if a licensed electrician and plumber install it within 30 days and you register within 30 days.
Is the Stiebel Tempra 24 better than the EcoSmart ECO 24?
Both are 24 kW, so flow is the same: about 2.4 GPM from 37°F water at a 105°F setting. The Tempra 24 needs two 50 A breakers against the ECO 24’s three 40 A, recommends 150 A service against 200 A, and rates 0.97 UEF against 0.93. The ECO 24 has the lifetime warranty.
How many amps does a Stiebel Tempra 24 need?
100 A total, on two 50 A double-pole breakers with two runs of 8/2 copper wire. Stiebel recommends at least 150 A main service, depending on the rest of the house’s load.
How many amps does an EcoSmart ECO 36 need?
150 A total, on four 40 A double-pole breakers with four 8 AWG runs. EcoSmart recommends 300 A household service for it.
What is the difference between the Tempra Trend and Tempra Plus?
Same elements, wiring and warranty at each size. The Plus adds a flow readout in gallons per minute, a running cost-savings estimate, two preset buttons and, per Stiebel’s spare-parts list, an Advanced Flow Control motorized valve. Both have the digital temperature display, capacity bar, Tmax limit and display lock.
What is the Stiebel Eltron tankless warranty?
7 years against leaks and 3 years against failed parts, from the purchase date. Register within 90 days on Stiebel’s website. Labor, freezing, hard water and moving the heater are excluded.
Does the EcoSmart lifetime warranty have conditions?
Yes. For the ECO line, a licensed electrician and plumber must install it within 30 days of receipt, with proof, and you must register within 30 days or the warranty is void. Scale, freezing and failing to purge air are excluded, and labor isn’t covered.
Why is my Stiebel Eltron tankless not heating?
Stiebel’s manual lists a clogged filter screen or aerator, a stuck flow sensor, flow above the heater’s capacity, low voltage, scale on the elements and a tripped safety thermal cutout. Turn off the breakers before you check anything inside.
Can an electric tankless heater run on 208 V?
Yes, at reduced output. Stiebel’s Tempra 24 makes 18 kW at 208 V instead of 24. EcoSmart says its ECO models give 75% capacity at 208 V after a jumper change.
Do electric tankless water heaters need a relief valve?
Both makers say UL 499 doesn’t require one. EcoSmart notes that Massachusetts and Kentucky do, and Stiebel says to fit one if your inspector requires it. Check your local code.
How we compared them
Why trust us
Written by Isaac Daniels, a licensed journeyman plumber in Georgia (license #JP507711). Specs, wiring and warranty terms come from EcoSmart’s and Stiebel Eltron’s own spec sheets, manuals and warranty text; recall facts from CPSC; seller and stock from Amazon’s Creators API.
How we compare
Only what EcoSmart, Stiebel Eltron, CPSC and the Amazon listings publish, read Oct 21, 2026.
No score on any heater, because breaker fit and incoming water temperature decide the right one, not a single number.
Flow: EcoSmart’s zone tables as published. Stiebel’s flow is kW × 6.824 ÷ temperature rise, which reproduces Stiebel’s own rise table.
Links only to listings that were new, in stock and the buy-box offer at our check.
EcoSmart ECO 8 and ECO 11 specifications sheet (kW, amps, breaker, panel, UEF, wire, compression fittings, size, weight, zone flow table): ecosmartus.com, updated 2024-04-17, read Oct 21, 2026.
EcoSmart ECO use and care manual (clearances, relief valve, Massachusetts and Kentucky, pressure, air purge, electrical table, 208 V jumper, flow regulators, troubleshooting, maintenance): ecosmartus.com, 2024-04-17, read Oct 21, 2026.
EcoSmart ECO limited lifetime warranty (term, 30-day install and registration, licensed installers, exclusions, returns): ecosmartus.com, read Oct 21, 2026.
Stiebel Eltron Tempra Trend and Plus technical specifications, rev. 6.2025 (item numbers, kW at 240 and 208 V, amps, breakers, wire, temperature rise, activation flow, weight, size, pressure, UEF, main service recommendations): stiebel-eltron-usa.com, read Oct 21, 2026.
Stiebel Eltron Tempra Trend and Plus installation and operating instructions (registration, warranty, mounting, clearance, freezing, connectors, relief valve, 68–140°F range, display, Tmax, display lock, Plus features, troubleshooting, spare parts including the Plus-only Advanced Flow Control valve): stiebel-eltron-usa.com, read Oct 21, 2026.
Amazon listings for the Tempra 24 Trend, Tempra 20 Trend, ECO 36 and ECO 11 (seller, condition, stock, brand and model): read through the Creators API, Oct 21, 2026, 10:58 AM.
CPSC recall database searched for EcoSmart and Stiebel Eltron: Oct 21, 2026, 10:54 AM.
