Tankless Water Heater Electric 18kW at 240 Volt
- Water Heater
- 18000 watts
- 18000 watts
- Battery
Real on-demand output for a shower, but the 76-amp electrical requirement is the real decision point here, not the unit itself.
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How it ranks among the 10 water heaters we track
4.3★ across 743 Amazon ratings, Bayesian-smoothed toward the category average.
743 Amazon ratings, weighted on a log scale so huge counts don't drown everything.
50+ bought on Amazon last month.
Brand identity, imagery, description and spec coverage.
The ProductDome score is separate from the Amazon rating shown above: it combines the Bayesian-smoothed Amazon rating with evidence volume, tracked demand, and data quality across the 10 water heaters we track - how the scorecard works · full water heaters data report. Confidence: high - strong rating volume and complete data.Updated 8 days ago. Data-computed, not a hands-on test. Compiled by the ProductDome Research Team.
Overview
The Thermomate ET180 is a tankless electric water heater rated at 18kW on a 240-volt supply, built to deliver hot water on demand for a shower or similar indoor fixture rather than storing a reserve in a tank.
This is a different category of heater than the mini-tank units in this lineup: instead of storing and reheating a few gallons, it heats water as it flows through, rated up to 4.4 gallons per minute depending on incoming temperature. That output comes at a real electrical cost. Thermomate specifies a draw up to 76 amps and calls for two double-pole 40-amp breakers on two 8AWG wires, which is a dedicated circuit most homes will need an electrician to run. Self-modulating control adjusts power draw to the actual flow and incoming temperature rather than running at full output constantly.
- 18kW tankless at 240V
- Up to 4.4 GPM flow rate
- 80-140 F digital adjustment
- Two 40A double-pole breakers required, 76A draw
Who it's for
Suited to a homeowner replacing or supplementing a shower's hot water supply who can install or already has the electrical capacity for an 80-amp dedicated circuit. Not the right choice for a single-sink add-on, where the smaller mini-tank units in this category are the easier and cheaper fit.
Strengths and trade-offs
Drawn from this product's published specifications.
- On-demand output up to 4.4 GPM with no tank to run out
- Self-modulating power draw based on flow and temperature
- Compact wall-mounted footprint at 17.12 x 13.12 x 3.12 inches
- ETL certified with no-water auto shutoff and leak protection
- Requires an 80-amp dedicated circuit with two 40-amp breakers
- Needs two 8AWG wires, likely an electrician install
- Not sized for a single small sink where a mini tank is simpler
Performance notes
Self-modulating operation is the core of how this unit performs: it reads incoming water temperature and flow rate and adjusts heating output accordingly, aiming to hold a stable output temperature rather than swinging hot and cold as demand changes. The digital display allows 1-degree adjustments across an 80-140 F range. Because there is no tank, hot water starts in about 3 seconds and does not run out the way a stored reserve can, but the tradeoff is the heavy amperage draw needed to heat water on demand rather than gradually.
Specifications
| Brand | thermomate |
|---|---|
| Model | ET180 |
| Dimensions & fit | |
| Item Dimensions W x H | 13.1 × 17.1 inches |
| Item Depth | 3.1 inches |
| Capacity & performance | |
| Heat Output | 18000 watts |
| Maximum Temperature | 140 °F |
| Flow Rate | 4.4 gpm |
| Power & efficiency | |
| Wattage | 18000 watts |
| Power Source | Battery |
| Voltage | 240 volts |
| Construction & materials | |
| Material Type | Alloy Steel |
| Color | Gray |
| Compatibility & installation | |
| Mount Type | Wall |
| Included components | |
| Included Components | Mount Kit |
| Other details | |
| Number of Items | 1 |
| Item Type Name | tankless water heater |
| Manufacture Year | 2024 |
| Special Features | Instant hot water, Leaking free and maintenance free heating element |
| Style Name | 18kW |
| Maximum Pressure | 150 psi |
Other thermomate water heaters
How it compares
This product against the closest alternatives we track in water heaters.
| Product | Amazon rating | Ratings | ProductDome score |
|---|---|---|---|
| Tankless Water Heater Electric 18kW at 240 VoltThis product | 4.3 / 5 | 743 | 3.9 / 5 |
| Stiebel Eltron 233219 2.5 gallonStiebel Eltron | 4.6 / 5 | 462 | 4.2 / 5 |
| CAMPLUX 5L Portable Tankless Water HeaterCamplux Enjoy Outdoor Life | 4.2 / 5 | 3,346 | 4.1 / 5 |
| EcoSmart ECO 8 Tankless Water HeaterEcoSmart | 4.2 / 5 | 709 | 4.0 / 5 |
| GASLAND BS158 Outdoor Portable Gas Water Heater 1.58GPMGasland | 4.3 / 5 | 1,400 | 3.9 / 5 |
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Questions about the thermomate ET180
Common buyer questions answered straight from the product spec data - no fluff, no "it depends".
What breaker size does the ThermoMate ET180 need?
Thermomate specifies an 80-amp circuit using two double-pole 40-amp breakers on two 8AWG wires, drawing up to 76 amps.
How fast does hot water arrive with a tankless unit like this?
Being tankless, it heats on demand and Thermomate lists hot water starting in about 3 seconds, with no stored reserve to run out.
What is the maximum flow rate?
Up to 4.4 gallons per minute, though actual flow depends on the incoming water temperature and the target temperature set on the digital display.