Choosing a whole house electric heater means balancing hot water flow, electrical capacity, and efficiency. Below is a concise comparison of the five selected tankless electric units chosen for whole-house use, followed by objective product breakdowns and a detailed buying guide.
| Product | Rated Power | Reported Flow Rate | Notable Features |
|---|---|---|---|
| Rheem 18kW Tankless Electric Heater | 18 kW | Up to 4.4 GPM | External thermostatic control, self-modulating, field serviceable |
| Rheem RTEX-24 24kW Electric Heater | 24 kW | Up to 5.9 GPM | Digital temp display, self-modulating power |
| Orbek 18kW On-Demand Water Heater | 18 kW | Up to 4.17 GPM | Water-electric separation, quick heat, ETL certified |
| ThermoMate 18kW On-Demand Heater | 18 kW | Noted as instant hot in 3 seconds | Self-modulating, digital 1° increments, scale-resistant design |
| WINTEMP 27kW Whole House Heater | 27 kW | Up to 6.3–6.5 GPM (listed) | WiFi control, LED display, high capacity for multiple points |
Rheem 18kW Tankless Electric Heater
This Rheem unit is an 18 kW electric tankless heater designed for compact whole-house or multiple-point use. The manufacturer highlights an external digital thermostatic control with LED display and +/-1° accuracy for temperature setting.
Key technical points include self-modulation that adjusts power to match hot water demand, and two copper immersion heating elements that are field serviceable. The unit lists a flow capacity up to 4.4 GPM, which is useful for 1–3 simultaneous fixtures depending on inlet water temperature.
Installation considerations: this model is intended for hardwired installation; confirm breaker and wire sizing with an electrician. The field-serviceable elements may simplify repairs compared to sealed units.
Rheem RTEX-24 24kW Electric Heater
The RTEX-24 is a 24 kW tankless electric heater aimed at higher-flow whole-house needs. Rheem lists a maximum flow rate of up to 5.9 GPM, which supports multiple simultaneous showers or fixtures in moderate climates.
Features include an ON/OFF dial control with adjustable digital temperature display and self-modulating power control for stable output as flow conditions change. As an electric unit, it requires adequate circuit capacity and proper wiring; confirm compatibility with your home’s service.
This model can be selected when the household requires a higher continuous GPM than lower-kW units can provide. Evaluate incoming groundwater temperature and expected simultaneous demand to determine suitability.
Orbek 18kW On-Demand Water Heater
The Orbek 18 kW electric tankless heater lists up to 4.17 GPM and is positioned for 2–3 point-of-use scenarios across a home. The product notes the need for 2 x 240V/40A two-pole breakers and 8 AWG wiring, which is critical to verify before purchase.
Design highlights include water-electricity separation to reduce scale and corrosion, and fast heat-up time with on-demand output in seconds. The manufacturer states potential energy reductions compared with storage tank heaters.
Consider this unit if your electrical panel can accommodate the specified breakers and if your typical simultaneous demand fits within the listed GPM. ETL certification is mentioned for safety verification in the product listing.
ThermoMate 18kW On-Demand Heater
ThermoMate’s model is an 18 kW on-demand electric heater emphasizing rapid response and energy savings. The listing highlights instant hot water in about 3 seconds and self-modulating technology that adjusts output to flow and inlet temperature.
This unit advertises digital temperature control with 1° increments and a design that separates the heating element from the water path to minimize scale buildup. The product notes it requires a substantial electrical supply — specifically 80A (two sets of 40A double-pole breakers) per the listing — so electrical planning is essential.
ThermoMate promotes high thermal efficiency and reduced operating cost compared to storage tanks. Confirm panel capacity and professional installation to meet the listed breaker requirements safely.
WINTEMP 27kW Whole House Heater
The WINTEMP unit is the highest rated among these selections at 27 kW, with a reported maximum flow of up to 6.3–6.5 GPM. The listing targets whole-house use with multiple simultaneous points of consumption.
Notable features include WiFi control, LED temperature display, and self-regulating power adjustment to maintain stable outlet temperatures as flow changes. The product calls out significant electrical demands: 3 x 40A double-pole breakers and 3 x 8/2 AWG wiring with a recommended 250A household power supply in the listing.
This unit is appropriate where higher continuous flow is needed and where the home’s electrical service can support the heavy load. Smart control features add remote monitoring and adjustments where that functionality is desired.
Buying Guide: How To Choose A Whole House Electric Tankless Heater
Selecting the appropriate electric tankless water heater requires examining several interdependent factors. Below are key considerations and comparison perspectives to guide a well-informed decision.
1. Assess Flow Rate Needs (GPM)
Flow rate (GPM) determines how many fixtures can run simultaneously. Estimate typical simultaneous demand: a shower ≈ 1.5–2.5 GPM, kitchen sink ≈ 1.5 GPM, dishwasher ≈ 1–2 GPM.
Match the unit’s listed GPM to expected simultaneous fixtures. Higher kW units generally deliver higher GPM, but actual performance depends on incoming water temperature.
2. Consider Incoming Water Temperature (Climate Impact)
Cold groundwater requires more energy to reach the desired outlet temperature. In colder regions, a higher kW unit or one with greater GPM capability is necessary to maintain shower temperatures during simultaneous use.
When comparing units, factor in the delta-T (temperature rise) needed. Manufacturers typically list max GPM at a specific temperature rise; check specifications or contact support for clarifications.
3. Electrical Service Capacity And Breaker Requirements
Electric tankless heaters can demand large continuous currents. Review your main service amperage, available panel spaces, and whether additional breakers and wiring runs are feasible.
Examples from the product specs: some 18 kW units list two 40A two-pole breakers; larger 27 kW units may require multiple 40A circuits. Always confirm requirements and hire a licensed electrician to assess panel upgrades and safety.
4. Self-Modulating & Temperature Stability
Self-modulating) units adjust heating output based on flow and inlet temperature, improving energy efficiency and stabilizing outlet temperature during variable demand.
Look for digital thermostatic controls and fine-grain temperature adjustment (1° increments where available) to maintain comfort and avoid swings that cause cold shocks during showers.
5. Certifications, Safety, And Serviceability
Choose units with safety certifications (ETL, CSA) when available. Serviceability features, like field-serviceable heating elements, can simplify repairs and extend service life.
Also evaluate installation notes such as water connections (NPT sizing) and whether the heater separates heating elements from water to reduce scale accumulation.
6. Installation Space And Plumbing Considerations
Tankless electric heaters are wall-mounted and compact, but allow clearance for wiring, access panels, and maintenance. Confirm inlet/outlet connections (e.g., 3/4″ NPT or 1/2″ NPT) and the need for pressure relief valves or isolation valves for servicing.
Short plumbing runs and point-of-use planning can improve performance and reduce hot water lag in larger homes.
7. Energy Efficiency And Operating Cost Perspectives
Electric tankless units typically have high thermal efficiency because they heat on demand and avoid tank standby losses. Compare manufacturers’ efficiency claims and evaluate how local electricity rates affect operating cost versus storage tanks.
Self-modulation reduces energy waste at low flow. Smart features like scheduling or remote control can help optimize usage patterns in some households.
8. Smart Features And Controls
Some models include WiFi control or remote monitoring for temperature adjustment and diagnostics. Decide whether remote features are important for your household management and whether the additional functionality justifies installation complexity.
9. Maintenance And Water Quality
Hard water accelerates scale buildup. Review the unit’s anti-scale design and plan for periodic descaling or water treatment if local water hardness is high.
Units that separate heating elements from the main water channel or specify reduced scale designs can lower maintenance frequency, but regular checks are still recommended.
10. Professional Installation, Permits, And Warranty
Hire a licensed electrician and plumber for installation to meet local electrical codes and plumbing requirements. Major electrical panel changes often require permits and inspections.
Consult the manufacturer’s documentation for warranty coverage and required professional installation conditions to maintain warranty validity.
Comparative perspective: choose higher-kW units when multiple simultaneous fixtures and cold inlet temperatures are expected; choose lower-kW but modern self-modulating units for smaller homes or milder climates where panel capacity is limited. Always match the unit’s electrical and plumbing requirements to your home’s existing infrastructure before purchase.