Choosing a tankless water heater for your whole home means matching its fuel, output, and installation needs to your household—not just picking the model with the largest flow-rate number. The options below include gas units for different levels of demand and an electric model that avoids venting. Before you buy, compare your incoming water temperature, the number of fixtures you may use at once, and your home’s gas or electrical capacity.
Table of Contents
Quick Comparison
| Water heater | Fuel and installation | Listed flow rate | Best suited for |
|---|---|---|---|
| Rinnai RXP199iN Condensing Smart Sense | Natural gas or propane; indoor or outdoor | Up to 11.1 GPM | High household demand and recirculation features |
| Westinghouse 8.1 GPM Outdoor Propane | Propane; outdoor | Up to 8.1 GPM | Several fixtures running at once |
| Ranein 5.3 GPM Indoor Natural Gas | Natural gas; indoor | Up to 5.3 GPM | Moderate household demand |
| Stiebel Eltron Tempra 24 Trend | Electric; indoor | Not specified in the supplied product data | Homes with sufficient electrical capacity |
| APUS 5.43 GPM Indoor Natural Gas | Natural gas; indoor | Up to 5.43 GPM | Smaller homes and moderate simultaneous use |
Our Picks: Best Tankless Water Heaters For Whole House Use reviews
Rinnai RXP199iN: Best for High Demand and Flexible Installation
The Rinnai RXP199iN is the highest-output option in this group, with a listed maximum flow rate of 11.1 GPM and heat output of 199,000 BTU. It runs on natural gas or propane, and its Versa Vent design allows indoor or outdoor installation. For outdoor placement, the specified RX-OVC vent cap is required.
Its internal recirculation pump and Smart-Circ feature are designed to learn household water-use patterns and schedule recirculation. That can help reduce the wait for hot water at taps, though results depend on the plumbing layout and setup. Wi-Fi control is available through a separate Control-R module, so it is not included as a built-in feature.
The compact wall-mounted unit may suit a busy household that wants to run several fixtures at once. Owners describe having a steady supply for a large household, while some also note that recirculation can make hot water arrive faster without running the tap while waiting. The main trade-off is installation complexity: Rinnai recommends a qualified technician, and the home must be set up for the selected fuel and venting arrangement.
Pros:
- Listed flow rate of up to 11.1 GPM
- Works with natural gas or propane
- Can be installed indoors or outdoors with the required outdoor accessory
- Built-in pump and Smart-Circ recirculation feature
Cons:
- Wi-Fi control requires a separate module
- Professional installation is recommended
Verdict: Choose the Rinnai if your home has high hot-water demand and you want fuel and installation flexibility, provided your installer confirms the unit is correctly sized for your conditions.
Westinghouse 8.1 GPM: Best Outdoor Propane Option for Multiple Fixtures
This outdoor-only propane heater has a listed maximum output of 180,000 BTU and flow rate of up to 8.1 GPM. The manufacturer says it is designed to support three to five fixtures at once, such as showers, sinks, a dishwasher, and laundry appliances. Actual performance depends on the temperature rise needed and the combined flow of the fixtures.
A wired digital controller is included, with a stated adjustment range of 95°F to 158°F. The unit also has freeze protection and a variable-speed combustion fan. It uses standard 3/4-inch NPT residential plumbing connections and requires 120V AC power, so outdoor placement does not mean the heater operates without an electrical connection.
Owners describe straightforward setup and stable temperatures in their installations. However, this model is not a fit if you need an indoor heater or use natural gas. Its stated warranty is two years for the complete unit and five years for the heat exchanger, so check the warranty terms and installation requirements before purchase.
Pros:
- Up to 8.1 GPM listed flow rate
- Designed for several simultaneous fixtures
- Includes a wired temperature controller
- Outdoor design includes freeze protection
Cons:
- Propane and outdoor installation only
- Requires 120V AC power as well as gas and plumbing connections
Verdict: Consider the Westinghouse if you use propane, have a suitable outdoor installation location, and need more capacity than the smaller indoor units offer.
Ranein 5.3 GPM: Compact Indoor Heater for Moderate Demand
The Ranein is an indoor natural-gas model rated at up to 5.3 GPM and 130,000 BTU. Its compact wall-mounted design is intended to save floor space, and it includes an LED display. The product information says it can serve three to five outlet points, but that claim should not be read as a guarantee that every outlet can run at full flow at the same time.
It has standard 3/4-inch NPT water and gas connections. The manufacturer also describes a fan that adjusts to changing conditions to support combustion. The unit’s maximum listed temperature is 130°F, which may be an important limit if you want a higher set temperature.
This may suit a household with moderate demand that wants to replace a tank heater with a compact indoor unit. The manufacturer notes that it is not recommended for locations above 2,000 feet. It also advises draining the unit during extended non-use in cold weather, so check the manual’s freeze-protection and winterization instructions for your situation.
Pros:
- Compact indoor wall-mounted design
- Up to 5.3 GPM and 130,000 BTU listed
- LED display and standard 3/4-inch connections
- Two-year manufacturer warranty stated in the product information
Cons:
- Natural gas only
- Not recommended for locations above 2,000 feet
Verdict: The Ranein is worth considering for moderate household use where natural gas is available, but check local elevation, temperature needs, and installation requirements first.
Stiebel Eltron Tempra 24 Trend: Best Electric Pick if Your Panel Can Support It
The Tempra 24 Trend is a 24 kW, 240V electric tankless heater. It needs hard wiring, and the manufacturer lists a minimum recommended electrical service of 150 A. Unlike gas models, it does not require venting, which can simplify placement—but only if your home’s electrical system can handle its demands.
Its compact design includes a digital temperature display and automatic modulation. The listed output temperature range is 68°F to 140°F. The product information also lists a seven-year leakage warranty and a three-year parts warranty. It is important to have an electrician assess your panel and wiring before buying; electrical capacity can be the deciding factor for this model.
Owners in warmer climates describe using it to replace a large tank, while others stress the need to confirm the electrical requirements before installation. Because the supplied specifications do not give a useful whole-house flow figure, do not assume that its 24 kW rating alone guarantees enough hot water for every home. Ask an installer to assess your incoming water temperature and expected simultaneous use.
Pros:
- No venting required
- Compact design with digital temperature display
- Automatic modulation and a stated temperature range up to 140°F
- Seven-year leakage and three-year parts warranties listed
Cons:
- Requires hard wiring and substantial electrical capacity
- Whole-house suitability depends on flow needs and local water conditions
Verdict: Pick the Tempra 24 Trend if you prefer electric operation, your electrical system can support it, and a qualified installer confirms its output suits your household.
APUS 5.43 GPM: Indoor Natural Gas Pick for Moderate Household Use
The APUS is an indoor natural-gas model rated at 120,000 BTU and up to 5.43 GPM. Its product information describes it as suitable for three to four water points, including two showers and a sink. That is a useful starting point, but the number of fixtures it can serve at once depends on their flow rates and the temperature rise required in your home.
The unit has an LED touchscreen, a stated temperature range of 95°F to 149°F in its feature description, and a low-flow start point of 0.66 GPM. The product details list a maximum temperature of 140°F, however, so confirm the usable temperature range with the manufacturer before purchase. It uses 120V AC for its controls and includes freeze protection; the manufacturer advises draining the unit below 41°F or during extended non-use.
This may be a fit for a smaller household looking for an indoor gas heater with a compact wall-mounted design. Its listed output is below the Rinnai and Westinghouse models, so it is not the strongest choice for high, simultaneous demand. The stated warranty is two years, and the included components are listed as including a vent pipe and installation kit.
Pros:
- Listed flow rate of up to 5.43 GPM
- Low-flow start point is listed at 0.66 GPM
- LED touchscreen and freeze-protection features
- Compact indoor wall-mounted design
Cons:
- Natural gas only
- Product information gives different maximum-temperature figures
Verdict: Consider the APUS for moderate demand if natural gas is available, but confirm the temperature specifications and have an installer verify its capacity for your home.
How to Choose a Whole-House Tankless Water Heater
Estimate Your Simultaneous Hot-Water Demand
List the fixtures and appliances that might run at the same time, such as showers, sinks, a dishwasher, or a washing machine. Add their expected hot-water flow rates to estimate the demand the heater must meet. A manufacturer’s suggested fixture count is a guide, not a promise of full flow at every outlet.
Account for Incoming Water Temperature
A heater must raise cold water to your chosen output temperature. The colder the incoming water, the more heating work the unit must do to supply the same flow. This is why a listed maximum GPM should not be treated as the guaranteed flow rate for every climate or household. Ask an installer to size the unit for your location and usage.
Choose the Right Fuel and Check Utility Capacity
Match the heater to a fuel source your home can use. The Rinnai supports natural gas or propane, the Westinghouse is propane-only, and the Ranein and APUS are natural-gas models. The Stiebel Eltron is electric and requires a 240V connection and substantial electrical service. Confirm gas-line capacity or electrical-panel suitability before ordering.
Plan for Indoor or Outdoor Installation
Check whether the model is approved for the location you have in mind. The Westinghouse is designed for outdoor installation, while the Ranein, Stiebel Eltron, and APUS are indoor units. The Rinnai can be installed indoors or outdoors with its required outdoor vent cap. Venting, clearances, plumbing, and local code requirements can affect the cost and feasibility of installation.
Consider Recirculation and the Wait for Hot Water
A tankless heater warms water on demand, but it does not remove the time it takes water to travel through long pipes. The Rinnai includes an internal recirculation pump and Smart-Circ scheduling. If faster hot water at distant taps is important, ask an installer whether recirculation makes sense for your plumbing and how it will affect setup and energy use.
Check Temperature Limits and Controls
Compare the model’s stated temperature range with your household needs, and check how the temperature is adjusted. The Westinghouse includes a wired controller; the Ranein has an LED display; the APUS has a touchscreen; and the Rinnai offers Wi-Fi control through a separate module. Confirm specifications with the manufacturer where product details conflict, as they do for the APUS temperature information.
Review Freeze Protection and Maintenance Needs
Freeze protection does not mean every installation is safe from freezing in all conditions. Follow the manufacturer’s instructions for drainage, power, and extended periods of non-use. Ask about routine maintenance, including flushing requirements, and make sure you understand the care needed for your water conditions and installation.
Get Installation and Warranty Details in Writing
Tankless heaters can require different gas, electrical, venting, and plumbing work than a tank replacement. Have a qualified professional check the site and estimate any required upgrades before you buy. Also read the warranty terms carefully, including registration requirements, coverage length, and which parts or labor are included.
Frequently Asked Questions
Can a tankless water heater supply an entire house?
Yes, if it is sized for the home’s simultaneous hot-water demand and the temperature rise needed. A whole-house model may still struggle if several high-flow fixtures run at once and exceed its capacity.
Does a higher GPM rating always mean better performance?
No. The listed flow rate is only part of the picture. Incoming water temperature, desired output temperature, and the flow of fixtures running at the same time all affect the hot water available.
Are tankless water heaters gas or electric?
They can use either. Gas models need the correct gas supply and venting arrangement, while electric models need enough electrical capacity. This selection includes both types, so check the utility requirements before choosing.
Will tankless heating make hot water arrive instantly?
Not necessarily. The heater warms water on demand, but water may still need time to travel through the pipes. A recirculation system, such as the one built into the Rinnai, may help reduce the wait when properly set up.
Does an outdoor tankless heater still need electricity?
Some do. The Westinghouse outdoor model requires 120V AC power in addition to propane. Check the specifications for any model you are considering rather than assuming outdoor installation means no electrical connection is needed.
Can I install a whole-house tankless water heater myself?
Installation can involve gas, electrical, venting, and plumbing work, and local rules may require a licensed professional. The Rinnai manufacturer recommends professional installation. Have a qualified installer confirm the site, capacity, and code requirements before purchase.
Final Recommendation
For households with high demand, the Rinnai RXP199iN stands out for its listed flow rate, dual-fuel compatibility, flexible installation, and built-in recirculation pump. The Westinghouse is a strong alternative if you specifically need an outdoor propane model. For moderate demand, consider the Ranein or APUS after confirming the capacity and temperature details for your home. Choose the Stiebel Eltron only after an electrician confirms your service can support its electrical requirements. In every case, proper sizing and professional installation matter as much as the heater’s headline output.
