A 30-amp tankless water heater is usually a point-of-use unit for one sink, not a whole-house heater. The right choice depends on your voltage, available circuit, water temperature needs, and how much hot water you expect to use at once. Our picks include compact heaters designed for a single outlet, plus a higher-output Stiebel Eltron option. Check each model’s electrical requirements carefully: “30 amp” does not mean every heater uses the same voltage, wiring, or breaker setup.
Table of Contents
Quick Comparison
| Product | Power and electrical details | Best for | Key feature |
|---|---|---|---|
| ThermoMate 6kW Tankless Water Heater | 6kW, 240V; draws 25A; requires a 30A breaker | Sink use where a dedicated 240V circuit is available | Digital temperature control and compact body |
| Stiebel Eltron DHX 3.5 Trend POU | 3.5kW, 120V; listed with a 30A breaker | Lower-flow point-of-use applications | Electronic temperature control and anti-scald limits |
| Stiebel Eltron DHC 8-2 Classic | 7.2kW at 240V or 5.4kW at 208V | A single sink needing more heating capacity | Hydraulic controls and copper-clad heating element |
| APUS 4500W Electric Tankless Water Heater | 4,500W, 220–240V; requires a 30A double-pole breaker | Compact, single-outlet installation | LED touch display and self-modulating operation |
Our Picks: Best 30 Amp Tankless Water Heater reviews
ThermoMate 6kW: Best All-Around Pick for a 240V Sink
The ThermoMate is a compact 240V heater for a single sink. Its 6kW heating system is specified to provide 1.0 gallon per minute at a 35°F temperature rise. That makes it a practical fit for handwashing and other modest point-of-use needs, but the output is not a promise of the same flow at every incoming water temperature.
The unit measures about 10.96 by 7.4 by 2.52 inches, so it can fit in tight spaces under or over a sink. It has a digital temperature display, touch controls, and temperature adjustment in one-degree increments. The manufacturer also lists a cast-aluminum heating element separated from the water line and a stainless-steel water tube.
Its electrical specifications need attention: the heater draws 25 amps at 240V and requires a 30A circuit breaker, at least 10 AWG wire, and hardwired installation. It is not a plug-in replacement for a standard outlet heater. Compared with the 120V Stiebel Eltron DHX, this model has more rated heating power, but it also requires a 240V supply.
Pros:
- 6kW output for a single point of use
- Compact size for under-sink or similar installations
- Digital display with one-degree temperature adjustment
- ETL listed, according to the product title
Cons:
- Requires 240V hardwiring and a dedicated 30A breaker
- Specified flow and temperature rise may not suit higher-demand use
Verdict: Choose the ThermoMate if you want a compact 240V sink heater with clear temperature controls and your electrical service meets its stated requirements.
Stiebel Eltron DHX 3.5 Trend: Best for a 120V Point of Use
The DHX 3.5 Trend is a 3.5kW, 120V point-of-use heater. Its lower power rating makes it a different kind of option from the 240V ThermoMate and APUS models. It may suit a single low-flow outlet where 120V power is the relevant constraint, but the supplied product information does not specify a flow rate or temperature rise.
Its electronic controls use a flow sensor and inlet and outlet temperature sensors, and the unit has an LCD screen with digital temperature adjustment. The stated output range is 68–140°F. Selectable anti-scald limits of 109°F, 122°F, or 131°F offer a way to cap the temperature setting for certain installations.
The product title specifies a 30A breaker, but the listing information also identifies this as a 120V heater. Confirm the exact wiring and circuit requirements in the manufacturer’s installation instructions before buying. Compared with the other picks, this model stands out for its control features and 120V design rather than high heating capacity.
Pros:
- 120V, 3.5kW design for a point-of-use application
- Electronic temperature control with an LCD screen
- Selectable temperature limits for added scald protection
- Can be used as a booster, according to the product description
Cons:
- Lower rated power than the 240V models in this comparison
- Product information does not state a flow rate or temperature rise
Verdict: Consider the DHX 3.5 if you need a 120V point-of-use heater and its lower output fits your use; verify the circuit details before installation.
Stiebel Eltron DHC 8-2 Classic: Best for More Heating Power
The DHC 8-2 Classic is a single-sink point-of-use heater with different power ratings for different supply voltages: 7.2kW at 240V or 5.4kW at 208V. Those figures are higher than the 3.5kW DHX 3.5, making the DHC 8-2 the more powerful Stiebel Eltron option in this lineup. The supplied information does not list its required breaker size, so check the installation manual and have an electrician confirm compatibility.
This model uses hydraulic controls and is described as operating quietly. Its copper-clad heating element and resettable high-limit safety switch are notable construction and safety features. The manufacturer also says the heater never dry-fires; installation should still follow the product instructions and applicable electrical and plumbing rules.
The DHC 8-2 may suit a sink where a lower-power unit is not the right match, especially when the supply voltage and circuit can support it. It is not presented as a whole-house heater, and the product details do not provide a flow-rate figure for comparing output under specific water conditions.
Pros:
- Higher rated power than the 3.5kW model in this group
- Supports 240V and 208V configurations
- Hydraulic controls are designed for quiet operation
- Copper-clad heating element and resettable high-limit switch
Cons:
- Breaker and wire requirements are not specified in the supplied product details
- Not identified as a whole-house heater
Verdict: The DHC 8-2 is worth considering for a single sink when you want more rated heating power, but confirm its electrical requirements before choosing it over the 30A-specific options.
APUS 4500W: Best Compact Option with a Touch Display
The APUS is a 4,500W electric tankless heater designed for one sink or another low-flow application. Its product information describes an adjustable outlet range of 85–131°F and says hot water may begin reaching the outlet in about three seconds under suitable inlet-water and flow conditions. That timing is conditional, not a guarantee for every installation.
At about 8.7 by 6.5 by 2.6 inches, this is the smallest listed unit by the dimensions provided. It uses an LED touch display and self-modulating operation, adjusting power based on flow and temperature conditions. The description also lists over-temperature, dry-burn, and leakage protection.
The APUS requires a dedicated 220–240V hardwired circuit, a 30A double-pole breaker, and 12 AWG copper wire, according to its product details. It is explicitly not intended for whole-house or multiple-bathroom use. Compared with the ThermoMate, it has lower rated power and a smaller stated body, while both are intended for single-outlet use.
Pros:
- Compact design for under-sink or nearby wall placement
- LED touch control with an adjustable 85–131°F range
- Self-modulating operation and listed safety protections
- Electrical requirements are clearly stated in the product details
Cons:
- Designed for a single low-flow outlet, not whole-house use
- Requires dedicated hardwired 220–240V power
Verdict: Pick the APUS if compact size and a touch display are priorities for a single sink, and your setup can meet its dedicated 30A circuit requirements.
How to Choose a 30 Amp Tankless Water Heater
Match the heater to its voltage and circuit
Start with the unit’s exact electrical requirements, not just the amp rating in its name or listing. The products here include 120V, 208V, 220–240V, and 240V models, and their breaker and wire requirements differ. For example, the ThermoMate draws 25A at 240V and calls for a 30A breaker, while the APUS specifies a 30A double-pole breaker and 12 AWG copper wire. Have a qualified electrician confirm that your panel, wiring, grounding, and available circuit are suitable.
Estimate your hot-water demand
These models are intended for point-of-use applications, usually one sink or another low-flow outlet. Heater capacity affects how much water can be heated and by how many degrees as it flows. The ThermoMate provides a stated flow and temperature-rise figure, while the other supplied product details do not give comparable figures. If you need hot water at several fixtures at once, a small point-of-use unit may not meet that need.
Consider incoming water temperature
The colder the water entering the heater, the more work the unit must do to reach your selected temperature. Actual hot-water flow can therefore vary with the incoming temperature and the outlet setting. Treat published performance figures as specific conditions rather than a guarantee of identical results in every home.
Check the installation location and plumbing
Measure the space near the sink and confirm that the heater’s water connections match your plumbing. The ThermoMate and APUS list 1/2-inch NPT water connections. Also plan for a suitable mounting location and the hardwired electrical connection. Follow the installation instructions and local plumbing and electrical codes.
Compare controls and safety features
Digital displays and touch controls make temperature adjustment easier to see, while sensors and temperature limits can help manage operation. The DHX 3.5 lists selectable anti-scald limits, and the APUS lists over-temperature, dry-burn, and leakage protection. Check the exact features for the model you choose, and do not assume that one unit’s protection features apply to another.
Be realistic about the term “30 amp”
A 30A breaker requirement does not tell you by itself how much hot water a heater can deliver. Voltage, wattage, incoming water temperature, and flow all matter. Some models in this guide are described with a 30A breaker, while the DHC 8-2 product details list power ratings but not its breaker size. Confirm the complete electrical specification for your chosen model before purchase.
Frequently Asked Questions
Can a 30A tankless water heater run a whole house?
The models in this guide are designed for point-of-use applications, such as one sink. They should not be treated as whole-house heaters. A home with several showers or fixtures may need a different type and capacity of water heater.
Does a 30A breaker mean the heater uses exactly 30 amps?
No. A breaker rating and a heater’s operating current are not the same thing. For example, the ThermoMate is specified to draw 25A at 240V and requires a 30A breaker. Always use the model’s installation instructions to confirm the circuit, wire, and breaker requirements.
Which of these models is designed for 120V power?
The Stiebel Eltron DHX 3.5 Trend is listed as a 3.5kW, 120V unit. Its product title specifies a 30A breaker. Verify the full installation requirements before connecting it.
Which option has the highest stated power rating?
The Stiebel Eltron DHC 8-2 is rated at 7.2kW at 240V or 5.4kW at 208V, the highest power figure among these picks. Its product information does not state a breaker size, so confirm that detail with the installation documentation.
Will these heaters provide hot water at the same flow in every home?
No. Flow and outlet temperature depend on factors such as the incoming water temperature and the heater’s capacity. The ThermoMate lists a specific flow at a stated temperature rise; other models do not provide comparable performance figures in the supplied information.
Can I install one of these heaters myself?
These models require electrical and plumbing connections, and several require hardwiring. The APUS description recommends installation by a qualified electrician and plumber. Follow the manufacturer’s instructions and local codes, and consult qualified professionals if you are unsure about your setup.
Final Recommendation
For a typical 240V single-sink application, the ThermoMate is the strongest all-around fit in this group because it combines 6kW of power with a stated flow figure, digital temperature control, and a clear 30A breaker requirement. Choose the Stiebel Eltron DHX 3.5 if you specifically need a 120V point-of-use model, or the APUS if compact size and touch controls matter most. The DHC 8-2 offers the highest listed power, but its breaker requirements need to be confirmed. In every case, match the heater to your actual hot-water demand and have the electrical requirements checked before buying.
