Most 120-volt tankless water heaters are small point-of-use electric units that need a dedicated circuit, not a standard wall outlet.
A 120-volt unit is not a shrunken whole-home heater — it’s a different tool with a smaller job. Voltage settles how much hot water you get, what circuit you need, and whether an electrician must open your panel.
US 120-volt models are point-of-use electric heaters rated roughly 1.75 to 3.5 kW. Whole-home tankless units are almost always 240-volt electric or gas-fired. A gas tankless heater listing 120 volts uses that current only for its fan, controls, and pump, never to heat water — the most common mistake in this category.
What Can A 120-Volt Tankless Water Heater Actually Power?
It serves one low-flow tap: a bathroom sink, laundry sink, shop sink, or single hand-wash station. It won’t feed a shower and kitchen faucet at once, or keep up with a dishwasher.
Output tracks incoming water temperature. Colder supply, less hot water.
Maximum flow runs 0.7 to 1.5 GPM, and most units need 0.25 to 0.32 GPM to switch on. These assume one fixture draws at a time; run two and both lose temperature.
Pressure caps matter too.
Circuit Rules That Decide The Install
Every unit in this group is hardwired. A 120-volt tankless water heater draws enough current to need a dedicated circuit back to the panel; a standard wall outlet cannot supply it.
| Model | Power Draw | Wiring And Flow Notes |
|---|---|---|
| Stiebel Eltron DHC 3-1 | 3 kW, 25 A | #10 AWG copper minimum; 1/2 in NPT; dedicated 30 A circuit, direct wired |
| Eemax FlowCo SPEX3012 | 3 kW, 25 A | 1.5 GPM max; 0.25 GPM to activate |
| Eemax FlowCo SPEX3512 | 3.5 kW, 29 A | #10 AWG recommended; 0.3 GPM turn-on |
| GE 3.5 kW point-of-use | 3.5 kW | 0.7 GPM; 5-year limited warranty |
| Rheem RTEX-04T | 3.5 kW, 29 A | 30 A breaker; 10 AWG wire; 0.3 GPM minimum flow |
| Rheem UPVA-35K 100 | 3.5 kW, 29.2 A | 30 A breaker; #10 AWG wire |
| Rheem UPVA-24K 100 | 2.4 kW | 5-year warranty |
| Rheem UPVA-18K 100 | 1.75 kW | 5-year warranty |
A full panel stops this project cold. With no open slot for a 25 to 30 amp circuit, no 120-volt model fixes that — and a 240-volt unit needs a double-pole breaker instead. Workable alternatives: a small under-sink tank heater or an electrician who can free up capacity.
Warranty terms and flow at your winter inlet temperature vary by model. Our tested 120-volt tankless water heater roundup compares the units that performed best on a single sink.
Three Assumptions That Sink A 120-Volt Install
Most returns trace back to one of three assumptions, each cheap to check before ordering.
- That tankless means 120 volts. The 120-volt models are a small slice; most tankless heaters are 240-volt electric or gas-fired.
- That 120 volts means a plug. Hardwiring is the norm — none of the models above runs on a cord.
- That one sink-sized unit can carry a house.
Before buying, match the unit to the fixture: measure the tap’s flow rate, check winter incoming water temperature, and confirm an open breaker slot for a 25 to 30 amp draw. When all three line up, a 120-volt point-of-use heater delivers hot water at one sink for far less wiring work than a whole-home system.
FAQs
Do 120-volt tankless water heaters plug into a wall outlet?
No. They are hardwired. Most draw 25 to 29 amps, well beyond a household outlet, so a dedicated circuit must run from the panel. Stiebel Eltron’s documentation calls for direct wiring on its 120-volt DHC 3-1.
Can a 120-volt unit handle a shower?
Not realistically. A shower needs a 240-volt electric or gas tankless heater.
How is a 120-volt gas tankless heater different from a 120-volt electric one?
The two share a voltage label and nothing else. A gas tankless water heater uses 120 volts only for its fan, control board, and pump while gas does the heating. A 120-volt electric tankless heater uses the electricity itself to heat water, which is why output stays at sink level.
References & Sources
- Stiebel Eltron. “Specification Sheet — Mini and Mini-E Tankless Water Heaters.” Supports the DHC 3-1 electrical ratings, flow rates at 55°F and 75°F, pressure limit, and wiring requirements.
- Rheem. “Residential Electric Tankless Water Heaters.” Source for RTEX-04T and UPVA series power draws, breaker and wire sizing, and warranty terms.
- Eemax. “FlowCo SPEX3512 Point-of-Use Tankless Water Heater.” Source for FlowCo power draw, recommended wire size, and activation flow.
