Plan the electrical supply before buying electric tankless
Electric tankless water heating can require several circuits and substantial electrical demand. Check the exact model and available supply before treating it as a straightforward replacement for a storage or gas heater.
A defined installation estimate. Clear charges before paid diagnostic work.
One model shows why the supply review matters
The Stiebel Eltron Tempra manual lists separate electrical requirements for each model and supply voltage. These figures illustrate the planning issue; they are not a circuit design for another heater or a calculation of your home’s capacity.
| Tempra 24 Plus example | Manufacturer requirement or rating | Homeowner implication |
|---|---|---|
| At 240 V | 24 kW rated input. | Account for this model’s demand in the electrical assessment. |
| At 208 V | 18 kW rated input. | The available voltage changes the model’s output; do not assume identical performance. |
| Circuit arrangement | Two 50 A double-pole breakers in the manual’s table. | Plan the required circuit arrangement, not just one available breaker position. |
Breaker spaces and service capacity are different checks
Several open panel positions do not establish that the electrical service can support a tankless installation. The assessment considers existing demand, the proposed heater, panel suitability and the actual supply. Adding the breaker ratings is not a substitute for a proper load calculation.
An upgrade is not automatic for every tankless project. If an evaluated supply change is needed, the electrical scope, actual serving utility and required approvals determine the sequence. A circuit installation by itself does not always involve utility work.
Sources: Stiebel Eltron Tempra manual, pp. 12-15. / Tampa Electric: Construction Services.
Compare alternatives before committing
Keep the electrical and water-heating decisions connected. A storage or heat-pump alternative may have different circuit needs; an electric tankless model must also suit the household’s hot-water requirements as evaluated by the qualified water-heater installer.
Obtain an electrical scope before placing a nonreturnable equipment order or promising an installation date. Route access, multiple circuits, disconnecting provisions, permit review and any confirmed supply changes can affect the project. Equipment price alone is not the installed project cost.
Sources: Rheem AP21914 Rev. 02, pp. 12, 18. / Stiebel Eltron Tempra manual, pp. 12-15. / City of Orlando: Get a Permit.
What to send for an electrical estimate
Provide the exact model or shortlist, current heater type, proposed location, ZIP and planned installation date. If the manufacturer offers separate 208 V and 240 V ratings, send that page too; the electrician will verify the property supply.
The water-heater installer should define plumbing, sizing for hot-water use, commissioning and other mechanical work. Mister Safety’s agreed electrical scope should identify the circuit work, connection and coordination responsibilities. Do not open the panel to gather information.
In Simple Terms
An electric tankless heater heats water as it passes through. Its small physical size does not tell you how much electrical supply it needs. Some models need several circuits, and the home’s available capacity must be evaluated separately from the number of empty breaker spaces.
Choose the heater and the electrical plan together. Checking this before purchase helps you compare a complete tankless project with storage or heat-pump alternatives and coordinate the electrical and plumbing appointments.
Your questions, answered.
Does two 50 A breakers mean my home needs a 100 A service upgrade?
No. Breaker labels are not a service-load calculation or an automatic upgrade size. The selected heater and the property’s overall electrical demand must be evaluated.
Will the same heater perform identically on 208 V and 240 V?
Not necessarily. The cited Tempra 24 Plus table lists different power ratings at those voltages. The water-heater installer must account for the available supply when selecting the model.
Can I get an installed price from the equipment price online?
No. Equipment cost and electrical, plumbing, permitting or supply-change costs are different parts of the project. Obtain a defined scope for each.
Keep planning with clarity.
Plan the electrical work before installation.
Considering electric tankless? Send the model shortlist and current water-heater setup so the electrical scope can be evaluated before purchase.
Clear scope before paid work.
A free estimate prices defined installation or upgrade work. Investigating an unexplained fault is paid diagnostic work; the charge is explained and approved before troubleshooting.
An existing circuit is not working? Ask about diagnostics.Based in Zephyrhills and the Tampa Bay area. We confirm availability for your Florida service address and project.
Our office answers 24/7. Arrival windows describe expected arrival, not a completion guarantee. View scheduling and fee details.
Read our current warranty terms. Qualifying work and disclosed discounted work have different coverage terms.
Research reviewed September 12, 2026. Exact equipment instructions, assessed conditions and the applicable jurisdiction govern the installation. Confirm current permit and code requirements for the project.
Sources and further reading
- Tempra Trend & Tempra Plus Operation and Installation
Stiebel Eltron · Current linked manual; publication date not established.
- Construction Services
Tampa Electric · Undated current page.
- 120 V Heat Pump Water Heater Use & Care / Installation, AP21914 Rev. 02
Rheem · AP21914 Rev. 02; copyright 2022.
- Get a Permit
City of Orlando · Undated current page.