Choosing the best electric tankless water heater for a whole house starts with two checks: how much hot water your household uses at once and whether your electrical service can support the unit. A heater’s advertised flow rate is not a guarantee at every inlet-water temperature, so a model that works well in a mild climate may struggle to supply several fixtures in colder conditions. Below, we compare the listed options, including two point-of-use or gas alternatives that may suit some homes but are not direct substitutes for a whole-house electric heater.
Table of Contents
Quick Comparison
| Product | Power or fuel | Listed maximum flow | Best fit |
|---|---|---|---|
| Rheem RTEX-24 24kW Electric Tankless Water Heater | 24 kW, 240V electric | Up to 5.9 GPM | Homes with suitable electrical service and moderate simultaneous hot-water needs |
| WINTEMP 27kW Electric Tankless Water Heater | 27 kW, 240V electric | Up to 6.5 GPM | Households needing higher listed electric output, if their service can support it |
| WINTEMP 18kW Electric Tankless Water Heater | 18 kW, 240V electric | Up to 4.3 GPM | Smaller hot-water loads or homes with less electrical capacity |
| Westinghouse 11kW WiFi Electric Tankless Water Heater | 11 kW, 240V electric | Up to 2.56 GPM | Point-of-use service, such as one shower or a small area |
| Rinnai RX180iN Condensing Tankless Water Heater | Natural gas or propane | Up to 10 GPM | A gas-powered alternative for homes open to a different fuel type |
Flow rates are the manufacturers’ listed maximums. Actual output depends on incoming water temperature, desired set temperature, flow, and installation conditions.
Our Picks: Best Electric Tankless Water Heater For Whole House reviews
1. Rheem RTEX-24: A Mainstream Whole-Home Electric Option
The Rheem RTEX-24 is a 24 kW, 240V electric tankless heater designed for whole-home use. Its listed maximum flow is up to 5.9 GPM, and its digital thermostat adjusts in one-degree increments from 80°F to 140°F. It heats water on demand and does not need venting, which can simplify placement compared with a gas tankless system.
The compact wall-mounted cabinet measures about 17.6 inches wide by 18.3 inches high and is listed at 3.5 inches deep. That saves floor space, but the electrical requirements are substantial: the product information calls for three 40-amp double-pole breakers, three sets of #8 AWG copper conductors with ground, and recommends at least a 200-amp household service panel. Have an electrician check the panel and installation plan before buying.
At its listed output, this is a strong candidate for a home with moderate overlapping hot-water use and adequate electrical capacity. Its flow rating does not guarantee that it can supply every fixture at once, especially where incoming water is cold. The product information lists a five-year leak warranty and a one-year parts warranty; confirm the terms that apply to your installation.
Pros:
- Designed for whole-home use, with a listed maximum flow of up to 5.9 GPM
- Digital temperature adjustment in one-degree increments
- Compact, wall-mounted design with no venting requirement
- Established brand and clearly stated electrical requirements
Cons:
- Requires substantial electrical capacity and dedicated circuits
- Actual flow can be lower than the listed maximum in colder-water conditions
Verdict: Choose the Rheem RTEX-24 if you want a whole-home electric model from a familiar brand and your electrician confirms your service can support it.
2. WINTEMP 27kW: The Highest-Output Electric Pick Listed
This WINTEMP model is a 27 kW, 240V electric heater with a listed maximum output of 6.5 GPM. It uses self-modulating controls that adjust power according to flow and incoming-water temperature, and it includes WiFi control. The manufacturer describes it as suitable for household showers and everyday use, but the flow figure alone cannot establish whether it will meet your home’s peak demand.
The unit is compact at about 11.1 inches wide, 19.2 inches high, and 4 inches deep, with 3/4-inch NPT water connections. Its listing specifies three 40-amp double-pole breakers and three 8/2 AWG wire runs, while also advising buyers to consult a qualified electrician. Because electrical-service recommendations can vary across the listing details, confirm the exact requirements in the current installation manual before purchase.
Some users report that installation can involve a meaningful additional cost for wiring, breakers, and plumbing changes. That is an important point for any high-output electric tankless heater: the unit price is only one part of the project. The listed ETL certification and safety protections are useful features, but they do not replace correct sizing and professional installation.
Pros:
- Highest listed flow among the electric models in this comparison
- Self-modulating operation adjusts power with flow and inlet temperature
- WiFi temperature control and a compact wall-mounted form
- Listing describes leakage, overheat, and dry-fire protections
Cons:
- Requires a major electrical installation that should be checked before purchase
- WiFi and the maximum flow rating do not guarantee whole-home performance in every climate
Verdict: Consider the WINTEMP 27kW if you need more listed electric capacity than the 24kW options provide and a qualified electrician confirms the service requirements.
3. WINTEMP 18kW: A Lower-Capacity Electric Choice
The WINTEMP 18kW is the smaller electric option from the same product line. It runs on 240V and lists a maximum flow of up to 4.3 GPM. The unit adjusts its power based on water flow and incoming temperature, and its WiFi feature lets you change the temperature remotely. Its listing describes it as suitable for residential shower use and everyday hot water.
At about 11.1 inches wide, 19.2 inches high, and 4 inches deep, it takes up little wall space. The stated electrical requirements are two 40-amp double-pole breakers and two 8/2 AWG wire runs, with a recommended 150-amp household service. Have an electrician verify the full load calculation for your home; a panel’s main rating by itself does not show how much spare capacity is available.
This lower-output model may suit a smaller household or a home with modest simultaneous hot-water demand. It has less listed flow than the Rheem 24kW and WINTEMP 27kW, so it is less compelling for multiple showers and other fixtures running together. The product information also lists a two-year limited warranty.
Pros:
- Lower electrical demand than the 24kW and 27kW choices
- Compact design with WiFi temperature control
- Self-modulating power use based on water flow and temperature
- Listed ETL certification and multiple safety protections
Cons:
- Lower maximum listed flow may limit simultaneous fixture use
- Still needs dedicated high-amperage circuits and a service check
Verdict: The WINTEMP 18kW is worth considering for a smaller hot-water load, but choose a higher-capacity unit if your household often uses several fixtures at once.
4. Westinghouse 11kW: Best for Point-of-Use Hot Water
The Westinghouse 11kW is a smaller 240V electric tankless heater intended for point-of-use service, not as the strongest choice for a whole house. Its listed maximum flow is up to 2.56 GPM, and the product information identifies one shower as a suitable use. It also offers app and voice control, an LED display, and temperature settings from 86°F to 140°F.
The wall-mounted unit measures about 9.5 inches wide by 14.2 inches high and 3.5 inches deep. Its stated electrical needs are one 50-amp double-pole breaker and 8 AWG wire, with an activation flow of 0.4 GPM. It is ETL certified and lists protections for leakage, overheating, dry firing, and high voltage.
Some users describe straightforward setup and dependable hot water in smaller spaces, while others note that temperature settings above 130°F can lead to an over-temperature shutdown in certain conditions. That makes careful setup important. For whole-home use, this heater’s modest flow rating is a clear limitation; it makes more sense near a single bathroom, cabin, or other limited demand area.
Pros:
- Small footprint suited to tight or point-of-use installations
- WiFi and voice control with a visible LED display
- Listed ETL certification and multiple safety protections
- Lower output than whole-home models can fit smaller hot-water needs
Cons:
- Not a strong fit for whole-house demand or multiple simultaneous showers
- Temperature behavior may require careful setup to avoid a high-limit shutdown
Verdict: Buy the Westinghouse for a limited point-of-use job, not as your main whole-house electric water heater.
5. Rinnai RX180iN: A Gas Alternative, Not an Electric Heater
The Rinnai RX180iN is included as a comparison point, but it does not meet the electric requirement in the target category. It is a gas-fired condensing tankless heater that works with natural gas or propane. Its listed maximum output is up to 10 GPM, and the manufacturer says it can serve up to six fixtures at once, depending on conditions and sizing.
This model is designed for indoor or outdoor installation, although the listing specifies that an RX-OVC vent cap is required for outdoor installation. It includes a Quick Flush feature and has a listed UEF of .98. WiFi control requires a separate Controlr module, and the manufacturer recommends professional installation.
Its higher listed flow may make it worth comparing if your home already uses gas or propane and you are open to changing fuel type. That is a different installation from an electric tankless replacement: fuel supply, venting, and professional setup all need to be considered. Do not select it if you specifically need an electric heater.
Pros:
- Listed flow of up to 10 GPM for larger hot-water loads
- Can run on natural gas or propane
- Indoor or outdoor installation options, with the required configuration
- Quick Flush feature and listed UEF of .98
Cons:
- Gas-fired, so it is not an electric tankless water heater
- WiFi control requires a separate module, and professional installation is recommended
Verdict: Consider the Rinnai only if you are open to a gas or propane system; for an electric-only project, choose one of the electric models above instead.
How to Choose an Electric Tankless Water Heater for Your Whole House
Estimate Your Peak Hot-Water Demand
Think about how many hot-water fixtures may run at the same time, not just how many people live in your home. A shower running while a dishwasher or another shower is in use creates a larger demand than one fixture used alone. Use the flow needs for your actual fixtures and compare them with the heater’s capacity at your expected inlet-water temperature.
Account for Incoming Water Temperature
Tankless heaters must raise incoming water to your chosen temperature. The colder the water entering the unit, the more heat the heater must add, which can reduce the flow it can deliver at the target temperature. A listed maximum GPM is not a promise that the heater will provide that flow in every season or region. Ask a qualified installer to size the system for local water conditions.
Check Electrical Service Before Choosing a Model
High-output electric tankless heaters can require multiple dedicated breakers and heavy-gauge wiring. Compare the exact requirements in the manufacturer’s installation manual with your panel, available breaker spaces, wiring route, and the rest of your home’s electrical loads. A recommended service-panel size is not the same as confirmation that your existing panel has enough capacity. Have an electrician make that assessment before you order.
Compare Output With Your Household’s Real Needs
The 27kW WINTEMP has the highest listed flow among the electric models here, followed by the Rheem 24kW and WINTEMP 18kW. The Westinghouse 11kW is listed for point-of-use use and has much less flow. Treat those figures as a starting point, then check the expected output at your inlet temperature and desired set temperature. A higher-capacity unit is only useful if your electrical system can support it.
Review Installation Requirements and Total Project Scope
Tankless installation may involve new circuits, breakers, wiring, plumbing changes, or other work. The compact size of the heater does not mean the installation is simple or inexpensive. Check the required water connections, mounting location, electrical clearances, and local code requirements with your installer. Professional installation is especially important for a high-amperage appliance.
Look at Controls, Safety Features, and Warranty Terms
Digital temperature control can make it easier to set a comfortable output, while WiFi features may let you adjust settings remotely. These extras should come after sizing and installation needs. Review the exact safety features, warranty coverage, and any registration or installation conditions in the product documentation. Warranty terms can differ by component and model.
Decide Whether Electric Is the Right Fuel
Electric tankless heaters avoid gas venting, but they can place a large load on a home’s electrical system. If your electrical service cannot support a whole-home electric unit, a gas model may be an alternative if your home has suitable fuel access and installation conditions. The Rinnai in this comparison is gas-fired, so it is not a substitute if your project requires an electric heater.
Frequently Asked Questions
Can an electric tankless water heater supply a whole house?
Yes, if the unit is correctly sized for the home’s peak demand and incoming-water temperature, and the electrical service can support it. A model’s whole-home label or maximum flow rating alone does not confirm that it will meet every home’s needs.
Which electric model in this comparison has the highest listed flow?
The WINTEMP 27kW lists up to 6.5 GPM, the highest among the electric options here. Actual usable flow depends on inlet-water temperature, desired temperature, and installation conditions.
Is the Rheem RTEX-24 suitable for multiple fixtures?
It is described as suitable for multiple fixtures and lists a maximum flow of up to 5.9 GPM. Whether that is enough for your household depends on which fixtures run at the same time and how cold the incoming water is.
Will a tankless electric heater work with my existing electrical panel?
It depends on your panel’s capacity, existing loads, available breaker spaces, and the heater’s specific requirements. Have a qualified electrician review the installation manual and assess your service before buying.
Is the Westinghouse 11kW a whole-house heater?
It is better suited to point-of-use service. Its listing gives a maximum flow of up to 2.56 GPM and identifies one shower as a suitable application, so it is not the strongest choice for broad whole-home demand.
Does the Rinnai RX180iN run on electricity?
No. It is a gas-fired tankless heater that uses natural gas or propane. Its listing includes a 120V electrical connection, but that does not make it an electric water heater.
Do tankless heaters provide hot water instantly at every faucet?
They heat water on demand, but hot water still has to travel through the plumbing from the heater to the fixture. The wait depends on the distance and layout of the pipes.
Final Recommendation
For a whole-house electric installation, the Rheem RTEX-24 is a balanced option if its listed capacity matches your household’s demand and your electrical service meets its requirements. The WINTEMP 27kW offers the highest listed flow among the electric models here, but its substantial electrical needs make an electrician’s assessment essential. Choose the WINTEMP 18kW for a smaller hot-water load, and reserve the Westinghouse 11kW for point-of-use service. The Rinnai is a gas alternative, not an electric pick. Before ordering any model, confirm the expected flow for your climate and the complete installation requirements.
