Tankless water heaters heat water as you need it instead of storing a tankful, which can save space and reduce standby heat loss. The right model depends on your home’s fuel source, electrical capacity, incoming water temperature, and how many fixtures you expect to use at once. These five options include electric and gas models for different household needs; check the installation requirements carefully before choosing.
Table of Contents
Quick Comparison
| Model | Type | Listed maximum flow | Best suited for |
|---|---|---|---|
| Rheem RTEX-24 | Electric, 24 kW | Up to 5.9 GPM | Homes with sufficient electrical capacity |
| MIZUDO 199,000 BTU | Natural gas, indoor | Up to 10.3 GPM | Busy households with multiple bathrooms |
| Rheem RTG Series | Natural gas, outdoor | 8.4 GPM at a 35°F rise | Homes suited to outdoor installation |
| Rinnai RX199iN | Condensing gas, indoor or outdoor | Up to 11.1 GPM | Homes needing flexible placement and high output |
| WINTEMP 18kW | Electric, 18 kW | Up to 4.3 GPM | Smaller or moderate-demand homes with suitable wiring |
Our Picks: Best Tankless Water Heaters For Homes reviews
1. Rheem RTEX-24: High-Capacity Electric Heating
The Rheem RTEX-24 is a 24 kW electric tankless heater designed to supply hot water on demand. Its digital controls let you set the temperature in one-degree increments from 80°F to 140°F. Because it uses electricity rather than gas, it does not need a fuel line or exhaust vent.
Its compact design can free up floor space compared with a traditional tank. Rheem lists flow of up to 5.9 gallons per minute, but actual output depends on the temperature rise needed and the number of fixtures running. A larger temperature rise—such as in a colder climate—can reduce the available flow.
The key question is whether your home’s electrical system can support it. This model calls for three 40-amp double-pole breakers, three sets of #8 AWG copper conductors with ground, and a recommended minimum 200-amp household service panel. Have a qualified electrician confirm compatibility before buying. Compared with the gas models here, the RTEX-24 avoids venting but places a substantial demand on the electrical panel.
Pros:
- Electric operation requires no gas connection or exhaust vent
- Temperature adjusts in one-degree increments
- Compact wall-mounted design saves floor space
- Can serve multiple fixtures when correctly sized for the home
Cons:
- Requires significant electrical capacity and dedicated breakers
- Actual flow varies with incoming water temperature and demand
Verdict: Choose the RTEX-24 if you want an electric whole-home option and an electrician confirms your panel and wiring can handle its requirements.
2. MIZUDO 199,000 BTU: Indoor Gas Option for Busy Homes
This MIZUDO indoor natural-gas model is rated at 199,000 BTU and lists flow of up to 10.3 GPM. The manufacturer describes it as suitable for simultaneous household hot-water use across multiple bathrooms, kitchen fixtures, laundry, and a dishwasher. As with any tankless heater, the flow you can get depends on the required temperature rise and how much hot water the household uses at once.
The unit has Wi-Fi app control, an LED display, and a stated temperature-control range up to 149°F. Its low-flow activation is listed at 0.53 GPM, which may help it respond to smaller draws. The sealed direct-vent setup uses a dedicated 3-inch-by-5-inch concentric vent kit, so installation involves more than simply connecting a gas line and water pipes.
MIZUDO lists CSA certification for indoor installation, a two-year full-unit warranty, and five-year heat-exchanger coverage. The product information says it is not recommended for elevations above 3,000 feet and calls for draining residual water if the unit will sit unused for an extended period in cold climates. Compared with the outdoor Rheem, this model can be placed inside, but it needs an appropriate vent route and qualified installation.
Pros:
- High listed flow for homes with several hot-water demands
- Wi-Fi app control and compatibility with Amazon Alexa
- Low-flow activation is listed at 0.53 GPM
- Indoor design can fit in a closet, basement, or laundry area when properly installed
Cons:
- Requires a dedicated vent kit and professional gas installation
- Not recommended for elevations above 3,000 feet, according to the product information
Verdict: Consider the MIZUDO for a high-demand home that needs an indoor natural-gas unit, provided its venting, elevation, and installation requirements fit your property.
3. Rheem RTG Series: Outdoor Gas Heating for Multiple Fixtures
This Rheem RTG Series model is a natural-gas heater designed for outdoor installation. It is rated at 180,000 BTU per hour and lists 8.4 GPM at a 35°F temperature rise. Since its rated flow is tied to a stated rise, use your local groundwater temperature and desired hot-water temperature to estimate whether it can meet your home’s needs.
Outdoor placement avoids the need for indoor exhaust venting, and the unit has a metal cabinet for wall mounting. Its digital control panel allows temperature adjustments in one-degree increments. The listed safety features include freeze protection and flame-failure protection, but the product’s outdoor location and local climate still matter when planning installation.
Rheem lists a 15-year heat-exchanger warranty and a five-year parts warranty. The product information recommends professional installation. Compared with the indoor MIZUDO and Rinnai models, this option is a more direct fit if you want a natural-gas heater mounted outside and have a suitable location for it.
Pros:
- Outdoor installation eliminates the need for indoor venting
- Listed output of 8.4 GPM at a 35°F rise
- Digital temperature control with one-degree adjustments
- Includes listed freeze and flame-failure protection
Cons:
- Requires a suitable outdoor mounting location and natural-gas service
- Flow capacity changes with temperature rise and simultaneous demand
Verdict: The Rheem RTG Series is a practical candidate when outdoor installation suits your home and its temperature-rise-based flow rating matches your expected use.
4. Rinnai RX199iN: Flexible Placement and High Listed Flow
The Rinnai RX199iN is a 199,000 BTU condensing tankless heater that supports natural gas or propane. Rinnai lists flow of up to 11.1 GPM and says the unit can serve up to seven fixtures at once. Those figures are maximum claims, not a guarantee for every home; actual performance depends on incoming water temperature and the fixtures in use.
One of its notable features is installation flexibility: the unit can be installed indoors or outdoors using the specified Versa Vent setup, with an RX-OVC vent cap required for outdoor installation. It also has a Quick Flush feature and a UEF rating of .98. Wi-Fi control requires a separate Controlr module, so it is not included as a standard built-in feature.
Rinnai recommends professional installation and provides product guides and sizing information to help match a unit to a home. Its stated residential warranty includes 15 years on the heat exchanger, five years on parts, and five years on labor when registered within 90 days of installation; otherwise, the labor coverage defaults to one year. Compared with the other gas picks, it offers the highest listed maximum flow here and supports either natural gas or propane.
Pros:
- Supports natural gas or propane
- Indoor or outdoor installation is possible with the required vent setup
- High listed maximum flow of up to 11.1 GPM
- Quick Flush feature and stated UEF of .98
Cons:
- Professional installation is recommended
- Wi-Fi control requires a separately purchased module
Verdict: Choose the RX199iN if you need a flexible, high-output gas model and are prepared to arrange professional sizing and installation.
5. WINTEMP 18kW: Compact Electric Heating with Wi-Fi
The WINTEMP 18kW is a 240V electric tankless heater with a listed maximum output of 4.3 GPM. It adjusts power use based on water flow and incoming temperature, and includes Wi-Fi control for remote temperature changes. Its compact dimensions—11.1 inches wide, 19.2 inches high, and 4 inches deep—may make it easier to fit in a tight utility area.
The manufacturer describes it as suitable for everyday residential use and homes with two to three bathrooms in mild to moderate climates. Treat that as a general guide rather than a promise of simultaneous hot water for every fixture: the 4.3 GPM maximum and your local temperature rise are important when sizing it. The listed installation requirements are also specific: a maximum amperage of 75A, two 40-amp double-pole breakers, and 2 x 8/2 AWG wiring, with a 150-amp household service recommended.
The unit is ETL certified and includes listed leakage, overheat, and dry-fire protections. It has a two-year limited manufacturer warranty. Compared with the larger Rheem electric model, this one has lower listed flow and less demanding stated electrical requirements, though a qualified electrician should still confirm that the home’s panel and wiring are suitable.
Pros:
- Compact design with Wi-Fi temperature control
- Self-modulating operation adjusts power to flow and temperature
- ETL certified with several listed safety protections
- Lower listed maximum amperage than the Rheem RTEX-24
Cons:
- Listed maximum flow is lower than the gas models in this guide
- Still requires dedicated wiring and electrical-system checks
Verdict: The WINTEMP is worth considering for a smaller or moderate-demand home that wants an electric unit with Wi-Fi, as long as its flow and electrical requirements suit the household.
How to Choose a Tankless Water Heater for Your Home
Choose the right fuel source
Start with the services already available in your home. Electric models avoid gas piping and combustion venting, but they can require substantial electrical capacity and dedicated breakers. Gas models need the correct fuel supply and a suitable exhaust setup; the Rinnai can use natural gas or propane, while the other gas models listed here are natural-gas units. Installation changes can add complexity, so confirm what your home can support before settling on a model.
Size for flow and temperature rise
Gallons per minute tells you how much hot water a unit may provide, but the listed maximum alone is not enough to choose a heater. Temperature rise is the difference between the incoming water temperature and the temperature you want at the tap. Colder incoming water requires more heating, which can reduce flow. Estimate which fixtures might run together—such as a shower and a dishwasher—and ask a qualified installer to size the unit for that demand.
Check your electrical panel or gas supply
Electric tankless heaters can draw a large amount of power while operating. Compare the model’s breaker, wire, and service-panel requirements with your home’s electrical system, and have an electrician verify the setup. For gas units, confirm that the existing gas service, piping, and venting plan meet the heater’s specifications. Do not assume a water-heater replacement will connect to existing services without changes.
Plan the installation location and venting
Measure the proposed space and check required clearances, water connections, and access for maintenance. An indoor gas unit needs an approved route for exhaust and combustion air; the MIZUDO specifies a concentric vent kit. An outdoor unit avoids indoor venting but still needs an appropriate mounting location. The Rinnai supports indoor or outdoor installation with the specified components, so check its setup requirements before planning the location.
Consider temperature controls and useful features
Digital controls help you set the target temperature, while Wi-Fi can make adjustments more convenient if you want remote access. Check whether connectivity is built in or requires an added module: the WINTEMP and MIZUDO list Wi-Fi features, while the Rinnai requires a separate Controlr module for Wi-Fi control. Features should come after correct sizing and installation compatibility.
Compare warranties and maintenance needs
Warranty coverage varies by component and may depend on registration or other conditions. Read the full warranty terms, including what is covered and for how long. Ask the installer what maintenance the heater needs in your area, especially if your water has mineral content that may require periodic flushing. Also consider cold-weather precautions for outdoor units or for systems that may sit unused during freezing conditions.
Frequently Asked Questions
Can a tankless water heater supply hot water to an entire house?
Yes, a properly sized unit can serve household fixtures, but its capacity is limited by flow and temperature rise. If several high-demand fixtures run at once, they may exceed the heater’s available output. Have a professional size the model around your household’s peak use.
Is an electric or gas tankless water heater better?
Neither type is best for every home. Electric models do not need gas or exhaust venting, but may require major electrical capacity. Gas models can provide high listed flow, but need a suitable fuel supply and venting or outdoor installation. Your home’s existing services and hot-water demand should guide the choice.
How do I know what flow rate my home needs?
List the hot-water fixtures you may use at the same time and estimate their combined flow. Then account for the temperature rise needed in your area. A plumber or installer can help compare those needs with a model’s output at the appropriate temperature rise.
Does a tankless water heater provide unlimited hot water?
It can keep heating water while there is sufficient fuel or electrical capacity, but it does not provide unlimited flow. If demand exceeds its capacity, the water may not reach the desired temperature or flow. Correct sizing is essential.
Can I install a tankless water heater myself?
These models may require dedicated electrical circuits, gas work, specialized venting, or other code-related work. The product information for several of these units recommends professional installation. Use qualified tradespeople and follow local requirements rather than assuming a standard tank replacement is straightforward.
Will an outdoor tankless water heater work in cold weather?
Some models list freeze protection, but that does not make every installation suitable for every climate or situation. Check the manufacturer’s instructions for the specific unit and ask an installer about local conditions, placement, and precautions during power outages or extended periods without use.
Final Recommendation
For a high-demand home that can support natural gas or propane, the Rinnai RX199iN stands out for its listed maximum flow and flexible installation options, though professional setup and the required vent components matter. If your home is suited to outdoor natural-gas installation, the Rheem RTG Series is another strong option. For electric heating, compare the Rheem RTEX-24’s higher listed flow with its substantial electrical requirements against the more compact WINTEMP 18kW. The best choice is the one a qualified installer confirms can meet your peak hot-water demand and work safely with your home’s electrical or gas system.
