Best Tankless LP Gas Water Heater: Top Picks Compared

A tankless LP gas water heater heats water as you need it, rather than keeping a tank hot around the clock. The right choice depends on how many fixtures you expect to use at once, how cold your incoming water gets, and whether you need an indoor or outdoor model. The options below range from compact outdoor units for smaller households to higher-capacity systems for homes with several bathrooms. Always confirm the exact fuel type, installation requirements, and local code requirements before buying.

Quick Comparison

Our Picks: Best Tankless Lp Gas Water Heater reviews

1. Westinghouse 5.1 GPM: A Practical Outdoor Pick for Smaller Homes

This outdoor Westinghouse model is rated for up to 5.1 gallons per minute and 120,000 BTU. The manufacturer positions it for households of two to four people and says it can support two to four fixtures at once. That makes it a possible fit for a smaller home, guest space, or light-duty business, though actual flow depends on incoming water temperature and how much hot water each fixture needs.

A useful feature is its low stated activation flow of 0.53 GPM, with a minimum water pressure of 15 PSI. That may help it operate with lower-flow taps or older plumbing. It also includes a wired controller with a stated adjustment range of 95°F to 158°F. The manufacturer claims temperature stability within ±1°F and a UEF above 0.81; treat those figures as product specifications, not a promise that every home will get identical results.

The outdoor wall-mounted design avoids using indoor floor space, but it also means you need a suitable exterior location and protection for exposed plumbing. The unit has built-in freeze protection, but the supplied product information warns that external pipes need separate insulation and that the heater must be drained if temperatures fall below freezing without continuous power.

Pros:

• Outdoor design saves indoor space.
• Low stated activation flow may suit some lower-flow plumbing setups.
• Includes a wired temperature controller.
• CSA/ANSI certification and several stated safety protections.

Cons:

• Its 5.1 GPM rating may not suit larger homes with several high-demand fixtures.
• Outdoor pipes need their own freeze protection.

Verdict: Choose this model if you want a smaller outdoor LP heater and your household’s simultaneous hot-water needs fit its capacity.

2. Westinghouse 8.1 GPM: Higher-Capacity Outdoor Hot Water

This larger Westinghouse outdoor unit is rated for up to 8.1 GPM and 180,000 BTU. Its product description says it can support three to five fixtures at once, making it a better starting point than the 5.1 GPM model for a home with multiple bathrooms or overlapping laundry and kitchen use.

The heater uses a wired controller and self-modulating water-and-gas controls. The manufacturer claims outlet temperature stability within ±1°F. It is designed for outdoor wall mounting, so there is no indoor vent route to plan, but you still need to select a suitable location and protect the connected pipes from freezing. The product information also specifies 3/4-inch NPT residential plumbing and 120V AC power.

Compared with the smaller Westinghouse, this model has more rated output for peak use. That extra capacity is only useful if your gas supply, plumbing, and incoming-water conditions support it. The listed warranty is two years for the complete unit and five years for the heat exchanger, so check the warranty terms and installation conditions before purchase.

Pros:

• Higher stated flow and BTU output than the 5.1 GPM Westinghouse.
• Outdoor installation keeps the heater out of living space.
• Includes a wired controller and freeze-protection features.
• Warranty information specifies separate coverage for the unit and heat exchanger.

Cons:

• Requires 120V power as well as a properly sized propane supply.
• Outdoor installation still requires a plan for cold-weather pipe protection.

Verdict: This is the stronger Westinghouse choice when your home needs more simultaneous hot-water capacity and an outdoor installation works for your property.

3. Rheem RTG Series 8.4 GPM: Indoor Capacity With an Important Fuel Check

The product title identifies this Rheem RTG model as a liquid propane heater rated at 8.4 GPM and 180,000 BTU. The description says it is an indoor, non-condensing unit with a direct-vent system and gives its 8.4 GPM figure at a 35°F temperature rise. It also describes a wall-mounted design for whole-home use.

There is a key detail to resolve before considering this unit: the supplied description also calls it a natural gas heater, despite the LP wording in the title. Fuel type is not interchangeable, so do not rely on the title alone. Confirm the exact model number, fuel configuration, and installation instructions with Rheem or a qualified installer before buying. The description lists a 15-year heat-exchanger warranty and a five-year parts warranty, but confirm the terms for the exact model.

If the LP version is verified, this model may suit a home looking for indoor installation and substantial output. It includes a digital temperature control and is described as having built-in freeze and flame-failure protection. Professional installation is specified, and the direct-vent arrangement means venting and clearances need careful planning.

Pros:

• High stated capacity of 8.4 GPM and 180,000 BTU.
• Indoor wall-mounted design with a direct-vent system.
• Digital temperature control and stated safety features.
• Product description lists extended heat-exchanger and parts warranty coverage.

Cons:

• The supplied title and description conflict on propane versus natural gas.
• Professional installation and indoor vent planning are required.

Verdict: Consider this Rheem only after confirming that the exact unit is configured for LP gas and that its venting and installation requirements fit your home.

4. Rinnai RSC199iP: High Output With Smart-Circ Recirculation

The Rinnai RSC199iP is an indoor propane tankless heater with a listed maximum flow of up to 11 GPM. The product description says it can serve as many as seven fixtures at once, though the actual number your home can run will depend on water temperature rise, fixture demand, and the installation. Its stated capacity makes it the highest-output option in this group.

Its Smart-Circ feature is designed to learn household hot-water use patterns and schedule the pump and recirculation accordingly. Recirculation can be useful when you want hot water to reach distant fixtures sooner, but it requires a compatible plumbing setup. The description says a Wi-Fi control module is not included, so don’t assume the heater offers app control by itself.

This is a more involved option than the outdoor Westinghouse heaters. Rinnai recommends professional installation, and an indoor system needs suitable venting and placement. The product information lists separate residential warranty periods for the heat exchanger, labor, and parts; read the current warranty terms carefully before choosing it.

Pros:

• Highest listed maximum flow in this comparison.
• Smart-Circ scheduling is designed to adapt to household usage patterns.
• Indoor design and multiple venting options may suit different layouts.
• Product information provides separate warranty coverage for key components and labor.

Cons:

• Professional installation is recommended.
• The Wi-Fi control module is not included, and recirculation needs a compatible setup.

Verdict: Choose the Rinnai if you need high capacity and can make use of its recirculation features, with a qualified installer handling the system design.

5. MIZUDO 5.1 GPM: Flexible Placement and App Controls

This MIZUDO propane model is rated for 120,000 BTU and up to 5.1 GPM, putting it in the same general capacity class as the smaller Westinghouse. Its product information describes indoor or outdoor installation, but conversion accessories are required and must be purchased separately. Confirm which configuration and accessories you need before planning the installation.

The unit offers Wi-Fi and app controls for adjusting temperature, checking energy use, and receiving maintenance notifications, according to the product description. It also claims temperature stability within 1°F and lists a copper heat exchanger and stainless steel combustion chamber. Those material details may interest shoppers comparing construction, but they do not replace checking the full installation and maintenance instructions.

The listing describes protections for freeze conditions, dry burning, flame failure, and exhaust blockage. As with any tankless heater, installation must match the fuel supply, venting arrangement, and local requirements. The listed warranty is two years for the unit and five years for the heat exchanger. Since indoor use depends on separately purchased accessories, this model’s flexibility comes with added planning.

Pros:

• App controls provide remote temperature adjustment and maintenance notifications.
• Can be configured for indoor or outdoor use with the required accessories.
• Includes stated safety protections and freeze protection.
• Listed warranty separates unit and heat-exchanger coverage.

Cons:

• Indoor/outdoor conversion accessories are an extra purchase.
• Its 5.1 GPM rating may be limiting for homes with high simultaneous demand.

Verdict: The MIZUDO is worth considering if app control and placement flexibility matter more to you than having the highest flow capacity.

How to Choose the Best Tankless LP Gas Water Heater

Size the Heater for Your Peak Hot-Water Demand

Think about how many hot-water fixtures might run at the same time, not just how many people live in your home. A shower running while the dishwasher and a sink are in use creates a different demand from one shower at a time. Compare that peak use with the heater’s flow rating, and remember that the published maximum may not reflect the flow available under your home’s temperature conditions.

Account for Incoming Water Temperature

A tankless heater has to raise the incoming water to your chosen temperature. Colder incoming water requires a larger temperature rise, which can reduce the flow available at your desired output temperature. Look for performance information that states the temperature rise, such as the Rheem description’s 8.4 GPM figure at a 35°F rise. Ask an installer to size the unit for your local conditions and actual household demand.

Confirm the Fuel Type and Gas Supply

Make sure the exact model is designed for liquid propane, not natural gas. The Rheem listing included here has conflicting fuel descriptions, which makes confirmation especially important. Your installer should also check that the propane supply and gas piping can meet the heater’s requirements. Do not assume that a gas connection is correctly sized just because it already serves another appliance.

Choose Indoor or Outdoor Installation

An outdoor heater can save indoor space and avoid planning an indoor vent route, but it needs a suitable exterior location and protection for the connected plumbing. An indoor model needs an approved venting arrangement, proper clearances, and a location that works with the home’s layout. Check local codes and the manufacturer’s installation instructions before choosing based on convenience alone.

Understand Freeze Protection and Power Needs

Built-in freeze protection does not necessarily protect exposed water pipes. The Westinghouse outdoor model information specifically says external pipes need separate insulation and that the unit should be drained if temperatures drop below freezing without continuous power. Check what freeze protection covers, whether the heater needs electricity to operate that protection, and what steps are required during a power outage or extended vacancy.

Compare Controls and Recirculation Features

A wired controller can make it easier to adjust temperature, while app control may be useful if you want remote access or maintenance notifications. Recirculation can help hot water reach fixtures sooner, but it depends on compatible plumbing and may require additional components. Check whether a control module, conversion kit, or other accessory is included or sold separately.

Review Installation, Warranty, and Ongoing Care

Gas tankless heaters involve fuel, water, electricity, and sometimes venting, so use a qualified professional and follow local requirements. Before purchase, compare the warranty for the heat exchanger, other parts, and labor, and check any conditions that apply. Also plan for the maintenance required by the manufacturer and make sure the installation leaves the unit accessible for service.

Frequently Asked Questions

What does LP mean on a tankless water heater?

LP means liquid propane. A heater designed for propane is not automatically suitable for natural gas, or vice versa. Confirm the fuel type for the exact model before buying or arranging installation.

How many gallons per minute do I need?

There is no single right number for every home. Add up the hot-water flow you expect from fixtures that may run together, then compare that demand with the heater’s output under the temperature conditions where you live. A qualified installer can help size the system accurately.

Can a tankless LP heater supply a whole house?

Yes, some models are designed for whole-home use, but the phrase does not guarantee that every fixture can run at once. Capacity depends on the heater’s output, incoming water temperature, and simultaneous household demand.

Do outdoor tankless heaters need freeze protection?

Yes. Outdoor units and exposed pipes need a cold-weather plan. Built-in freeze protection may protect parts of the heater but not external plumbing, and some protection depends on continuous power. Follow the specific manufacturer instructions for insulation, draining, and outages.

Does a tankless water heater need electricity?

Some models require an electrical connection for controls and operation. The Westinghouse 8.1 GPM product information, for example, specifies 120V AC power. Check the requirements for the exact model and installation location.

Is professional installation necessary?

Professional installation is strongly recommended for gas water heaters and is specified in the supplied information for some of these models. The installer can check fuel supply, plumbing, venting, electrical needs, clearances, and local code requirements.

Which option is best for a home with several bathrooms?

Start by comparing the higher-capacity choices, such as the Westinghouse 8.1 GPM, Rheem 8.4 GPM, and Rinnai model rated up to 11 GPM. The Rheem listing’s fuel description needs confirmation, and the best fit still depends on your actual demand and incoming water temperature.

Final Recommendation

For a smaller household that wants an outdoor LP unit, the Westinghouse 5.1 GPM is a straightforward option to investigate. The Westinghouse 8.1 GPM is a more suitable starting point when several fixtures may run at once. For high demand and recirculation features, consider the Rinnai, while confirming that its installation and accessories fit your home. The MIZUDO stands out for app controls and placement options, but requires extra accessories for conversion. Before choosing the Rheem, confirm that the exact model is propane-configured, since its supplied product information conflicts on fuel type. In every case, have a qualified installer verify capacity, fuel supply, and installation requirements.