ThermoMate ET180 Electric Tankless Water Heater 18 kW
- Wattage: 18000 watts
- Power Source: Battery
- Flow Rate: 4.4 gpm
- Maximum Temperature: 140 °F
Last refreshed Sep 8, 2026 · Based on the Amazon listing and published specifications, not hands-on testing.
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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ASIN: B08MJJHZ7JModel: ET180Category: Water Heaters
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.
Pros and cons
- 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 Depth | 3.1 inches |
| Item Dimensions W X H | 13.1 × 17.1 inches |
| Capacity & performance | |
| Flow Rate | 4.4 gpmhigher than 65% of 21 water heaters |
| Maximum Temperature | 140 °F |
| Heat Output | 18 KW |
| Power & efficiency | |
| Wattage | 18000 watts |
| Power Source | Battery |
| Voltage | 240 voltshigher than 78% of 38 water heaters |
| Construction & materials | |
| Material Type | Alloy Steel |
| Color | Gray |
| Compatibility & installation | |
| Mount Type | Wall |
| Included components | |
| Included Components | Mount Kit |
| Other details | |
| Maximum Pressure | 150 psi |
| Number Of Items | 1 |
| Style Name | 18kW |
| Special Features | Instant hot water, Leaking free and maintenance free heating element |
| Item Type Name | Tankless Water Heater |
| Manufacture Year | 2024 |
Closest rivals on specs
Titan N-160 Electric Tankless Water Heater 16 kW- Wattage 18000 vs 16000 watts (+13%)
- Item Depth 3.1 vs 2.7 inches (+15%)
Eemax HA027240 Tankless Electric Water Heater 18 kW- Flow Rate 4.4 vs 6 gpm (-27%)
Titan N-180 Tankless Water Heater 18 kW- Flow Rate 4.4 vs 7 gpm (-37%)
- Item Depth 3.1 vs 4.5 inches (-31%)
Frequently asked questions
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.