Installing an electric tankless water heater runs $1,642 to $1,925 when the panel already has enough capacity, per Homewyse, dated May 2026. The moment it does not, a panel or service upgrade commonly adds $1,500 to $4,500 on its own, per Fixr, dated January 31, 2025, often the single biggest swing in the job.
Hot Water Brief is an independent cost-research site. We are not a contractor and do not perform the work ourselves.
That $1,642 to $1,925 figure is not a general electric tankless price tag. It is what Homewyse prices for one job: a 5.3 gallon per minute unit with three 40 amp, 240 volt circuits already at the wall. The estimate excludes bringing wiring up to current code, electrical system modification, and permit or inspection fees. Nearly everything excluded is electrical, which is why installed cost can land close to the baseline in one house and thousands above it in the next.
For the equipment price against the installed price across gas and electric, see the electric tankless water heater cost guide; for how tankless compares to a tank swap, see the full cost breakdown. What follows is only the part that decides where your quote lands: the panel, the circuits, and the permit.
A single point-of-use electric tankless unit can draw 54 amps by itself, and a larger whole-house model needs two separate 40 amp breakers for 75 amps combined, per Rheem's published specifications for the RTEX-13 and RTEX-18. On an older 100 amp panel, that is a large share of the whole house's total capacity.
A tank-type electric water heater pulls current in short bursts as a heating element cycles on and off to hold a tank at temperature. A tankless unit pulls its full rated current continuously for as long as hot water is running, because it is heating the entire flow in real time rather than reheating a stored tank. That is the practical reason the breaker and wire sizes on a tankless spec sheet run larger than what the tank it replaces ever needed.
Both Rheem product spec sheets advise confirming the panel can handle the unit's power demand and checking available amperage first, since that is what decides whether this stays a self-contained water heater job or becomes a panel job with a water heater attached.
Breaker and wire size scale directly with the unit's kilowatt rating and are set by the manufacturer, not by preference. A 13 kilowatt point-of-use model needs a single 60 amp double-pole breaker on 6 gauge copper wire; an 18 kilowatt whole-house model needs two 40 amp breakers on 8 gauge copper wire, each on its own circuit.
| Model | Capacity | Breaker(s) required | Wire gauge (copper) | Amp draw | Source, dated |
|---|---|---|---|---|---|
| Rheem RTEX-13, point-of-use | 13 kW | 1 x 60A double-pole | 6 AWG | 54A | Rheem spec via wholesalewaterheater.com, accessed August 2026 |
| Rheem RTEX-18, whole-house | 18 kW | 2 x 40A double-pole | 8 AWG | 75A combined | Rheem spec via wholesalewaterheater.com, accessed August 2026 |
| Stiebel Eltron Tempra 12 to 36 range | 12 to 36 kW | 1 to 3 double-pole breakers, up to 50A each | 10 AWG to 6 AWG | Varies by model | gotankless.com electrical requirements chart, accessed August 2026 |
| Homewyse priced national installed job | 5.3 gpm | 3 x 40A, 240V | Not stated | Not stated | Homewyse, May 2026 |
Line up Homewyse's priced job, which assumes three 40 amp circuits at the unit, against the figures above: the single-breaker RTEX-13 sits well under that assumption, while the two-breaker RTEX-18 sits close to it. The published national number tracks a larger, whole-house unit more than the smallest point-of-use model, part of why a single-bathroom quote can land under the published range and a full-house quote can land over it.
Yes. Rheem's 18 kilowatt RTEX-18 needs two separate 40 amp double-pole breakers rather than one larger breaker, and Stiebel Eltron's largest Tempra models need up to three double-pole breakers as large as 50 amps each, per each manufacturer's published electrical requirements. Each breaker needs its own dedicated wire run back to the panel.
That matters for labor, not just parts. One circuit is one wire run from the panel to the unit; three circuits on a Tempra 29 or 36 class unit means three wire runs, three breaker slots, and three termination points. Stiebel Eltron's electrical requirements page states that if a home lacks the minimum household service specified for the model, upgrades will likely be required, and recommends 100 to 300 amps of service depending on the model chosen.
Breaker slots are also a physical limit, separate from amperage. A panel can be rated for enough total amperage and still be out of open slots for a second or third double-pole breaker, which alone can force a panel change even when the total amp math looks fine on paper.
A full panel upgrade from 100 amp to 200 amp service runs $1,500 to $4,500 nationally, averaging about $3,000, per Fixr, dated January 31, 2025. That is on top of the tankless installation itself, and in some jobs it is a bigger line item than the water heater.
| Panel or service work | Published national range | Typical | Source, dated |
|---|---|---|---|
| Panel upgrade, 100A to 200A, no relocation | $1,500 to $4,500 | about $3,000 | Fixr, January 31, 2025 |
| Panel relocation, if the panel has to move | additional $1,000 to $4,000 | not stated | Fixr, January 31, 2025 |
| Rewiring beyond the panel itself | $500 to $4,500 | not stated | Fixr, January 31, 2025 |
| Electrical permit fee | $50 to $300 or more | not stated | Fixr, January 31, 2025 |
| Licensed electrician labor | $40 to $120 per hour | not stated | Fixr, January 31, 2025 |
Stack the two ranges together and a job needing both lands at roughly $3,142 to $6,425, more than triple the baseline's low end. Where you land in that range depends almost entirely on how far your existing service is from what the unit needs, not on which brand of water heater you buy.
No. Homewyse's national installed price of $1,642 to $1,925 explicitly excludes permit and inspection fees, dated May 2026, and Fixr's panel upgrade data prices a separate electrical permit at $50 to $300 or more, dated January 31, 2025. Expect a permit line to sit outside whatever installed quote you are handed, not buried inside it.
Permit fees are set locally by the building department with jurisdiction over the address, which is why neither national estimator bakes a single figure into its published range. If your quote does not mention a permit line at all, that is worth asking about, since work on a dedicated electrical circuit, and on the panel itself if one is needed, typically needs its own inspection separate from the plumbing side of swapping the water heater.
Compare your panel's rated amperage against the manufacturer's stated recommended household service for the exact model you want, not the model's amp draw alone. Stiebel Eltron's published chart recommends anywhere from 100 to 300 amps of total household service depending on the Tempra model chosen, and states that upgrades will likely be needed if your home falls short.
Rheem's RTEX-13 and RTEX-18 spec sheets both carry the same instruction in different words: check available amperage on the panel and consult an electrician before assuming a swap is a straightforward job. What a panel is rated for and what it has left to give are two different numbers once every existing circuit is counted, and that count is a licensed electrician's load calculation, not a guess from the panel door label.
Every figure on this page is listed here with its publisher and date, so you can check it against the day you are reading this.
Prices move. The dates above are the point of citing them, so check them against the day you are reading this rather than assuming a figure published in 2025 or May 2026 still holds.
$1,642 to $1,925 nationally when the panel already has the needed capacity, per Homewyse, dated May 2026. If a panel or service upgrade is needed, add $1,500 to $4,500 on top, per Fixr, dated January 31, 2025. Those two ranges explain most of the spread between quotes.
Current draw scales with the unit's kilowatt rating faster than one breaker can safely carry. Rheem's 18 kilowatt RTEX-18 needs two separate 40 amp breakers for 75 amps combined, and Stiebel Eltron's largest Tempra models need up to three double-pole breakers, per each manufacturer's specifications.
Compare your panel's rated amperage and remaining headroom against the manufacturer's recommended household service for the specific model, which Stiebel Eltron publishes as 100 to 300 amps depending on the unit. Rheem's RTEX-13 and RTEX-18 spec sheets both instruct checking available amperage and consulting an electrician first.
A 100 amp to 200 amp panel upgrade runs $1,500 to $4,500 nationally, averaging about $3,000, per Fixr, dated January 31, 2025. Relocating the panel adds $1,000 to $4,000 more, and rewiring beyond the panel itself runs $500 to $4,500, per the same source.
Not in the published national baseline. Homewyse's $1,642 to $1,925 installed figure, dated May 2026, excludes permit and inspection fees. Fixr prices a separate electrical permit at $50 to $300 or more, dated January 31, 2025, so budget for it as its own line.
Not automatically. It depends on how much spare capacity the existing panel already has, not just the new unit's rating. A 13 kilowatt model draws 54 amps on one breaker, while an 18 kilowatt model needs 75 amps across two breakers, per Rheem's specifications, so check headroom against the specific model.
Independent Research
Published ranges for tank and tankless replacement, the failures that justify a repair, and the ones that do not. Sourced, dated, and free to read.
