Section 10
Amp draw, breakers and main service size for electric tankless heaters
This table lists the amp draw, breakers and minimum main service that Stiebel Eltron and EcoSmart publish for 15 electric tankless models at 240 V. Minimum main service ranges from 100 A to 300 A. In an ADU fed from the main house, the feeder size can limit the heater size.
| Manufacturer | Model | Power | Amp draw | Breakers | Minimum main service |
|---|---|---|---|---|---|
| Stiebel Eltron | Tempra 12 Trend / Plus | 12 kW | 50 A | 1 x 50 A | 100 A |
| Stiebel Eltron | Tempra 15 Trend / Plus | 14.4 kW | 2 x 30 A | 2 x 30 A | 100 A |
| Stiebel Eltron | Tempra 20 Trend / Plus | 19.2 kW | 2 x 40 A | 2 x 40 A | 125 A |
| Stiebel Eltron | Tempra 24 Trend / Plus | 24 kW | 2 x 50 A | 2 x 50 A | 150 A |
| Stiebel Eltron | Tempra 29 Trend / Plus | 28.8 kW | 3 x 40 A | 3 x 40 A | 200 A |
| Stiebel Eltron | Tempra 36 Trend / Plus | 36 kW | 3 x 50 A | 3 x 50 A | 300 A |
| EcoSmart | ECO 8 | 8 kW | 33 A | 1 x 40 A DP | Not listed |
| EcoSmart | ECO 11 | 13 kW | 54 A | 1 x 60 A DP | Not listed |
| EcoSmart | ECO 18 | 18 kW | 75 A | 2 x 40 A DP | 150 A |
| EcoSmart | ECO 24 | 24 kW | 100 A | 3 x 40 A DP | 200 A |
| EcoSmart | ECO 27 | 27 kW | 113 A | 3 x 40 A DP | 200 A |
| EcoSmart | ECO 36 | 36 kW | 150 A | 4 x 40 A DP | 300 A |
| Stiebel Eltron | DHC-E 8/10 Classic (set to 9.6 kW) | 9.6 kW | 40 A | 1 x 40 A DP | Not listed |
| Stiebel Eltron | DHC-E 8/10 Classic (set to 7.2 kW) | 7.2 kW | 30 A | 1 x 30 A DP | Not listed |
| Stiebel Eltron | DHC-E 12 Classic | 12 kW | 50 A | 1 x 50 A DP | Not listed |
Sources: Stiebel Eltron Tempra[1] and DHC-E[2] technical specifications and EcoSmart product pages[3][4].
10.2 Service size by model
Stiebel Eltron lists 100 A main service for the Tempra 12 and 15 and 125 A for the 20. It lists 150 A for the 24, 200 A for the 29 and 300 A for the 36[1]. EcoSmart lists a 150 A panel for the ECO 18 and a 200 A panel for the ECO 24 and ECO 27. It lists 300 A for the ECO 36[3][4]. These are the manufacturers' minimums for the whole service. They do not account for the rest of the building's load.
Stiebel Eltron's footnote on breakers says overcurrent protection is sized at 100 percent of load, because tankless water heaters are treated as a non-continuous load. It calls for copper conductors rated 75 C or higher[1]. Local code can differ.
This page lists published numbers and is not wiring guidance. A licensed electrician runs the load calculation and does the work.