Westinghouse 120,000 BTU Natural Gas Tankless Water Heater Review: 5.1 GPM Whole-Home Hot Water With App Control

A tankless water heater can be a practical upgrade for households that want hot water on demand without dedicating floor space to a large storage tank. Instead of keeping dozens of gallons heated around the clock, a tankless system activates when hot water is requested and heats it as it passes through the unit.

This Westinghouse natural gas tankless water heater is designed for indoor residential use and combines a stated 120,000 BTU input, up to 5.1 gallons per minute of hot-water flow, smartphone control, an LED interface, a water-flow servo intended to stabilize outlet temperature, and built-in protection features such as freeze protection.

Its output places it in the mid-capacity range for whole-home tankless systems. It may be capable of serving several fixtures at once, but the real-world result depends heavily on incoming water temperature, desired outlet temperature, plumbing flow, and how many showers or faucets are operating simultaneously.

What Is the Westinghouse 5.1 GPM Tankless Water Heater?

This model is an indoor natural gas tankless water heater designed to produce hot water only when demand occurs.

The supplied specifications include:

• 120,000 BTU gas input
• Up to 5.1 GPM maximum flow
• Natural gas operation
• Indoor installation
• Smartphone app control
• LED control panel
• Water-flow servo
• Claimed ±1°F temperature stability
• Variable-speed fan
• Freeze protection
• CSA certification
• 3/4-inch NPT plumbing connections
• 2-year whole-unit warranty
• 5-year heat-exchanger warranty

It is marketed for both whole-home and some commercial applications, although actual suitability should always be based on calculated hot-water demand.

How a Tankless Water Heater Works

A conventional storage water heater keeps a reservoir of water hot until someone uses it.

A tankless model works differently.

When a hot-water fixture opens, water begins flowing through the heater. Sensors detect the demand, the gas burner activates, and heat is transferred into the water before it leaves the unit.

When the fixture closes, the burner shuts down.

This is why tankless systems are often described as "on-demand" water heaters.

Why On-Demand Heating Can Save Energy

A storage water heater continually loses heat through its tank walls and must periodically reheat the stored water.

A tankless system avoids much of that standby heating because it does not maintain a large reservoir at temperature.

Actual energy savings depend on:

• Household water usage
• Fuel prices
• Installation
• Existing equipment
• Temperature settings

A specific savings percentage should not be assumed without verified operating data.

Understanding the 120,000 BTU Rating

The burner is rated at up to 120,000 BTU according to the supplied information.

BTU measures heating capacity.

For tankless water heaters, burner capacity is especially important because the appliance must heat water while it is moving rather than gradually warming a storage tank.

More BTU Means More Heating Capability

In general, more burner capacity allows a tankless heater to support:

• Higher water flow
• Larger temperature rise
• More simultaneous demand

However, BTU alone does not determine performance.

The heater's design, efficiency, flow controls, and incoming water temperature all matter.

Maximum Flow of 5.1 GPM

The source lists a maximum output of up to 5.1 gallons per minute.

That is enough, under suitable conditions, for multiple household fixtures.

However, 5.1 GPM is a maximum rating rather than a guaranteed flow under all conditions.

Why Maximum GPM Needs Context

Tankless output falls as the required temperature rise increases.

If incoming water is relatively warm, the heater does not need to add as much heat.

If the inlet water is very cold, the unit must work harder to reach the same outlet temperature, reducing the maximum flow it can sustain.

This is one of the most important concepts when choosing a tankless heater.

Temperature Rise Matters More Than Household Size

A heater should not be selected solely based on statements such as "for a family of four."

Two homes with the same number of occupants can have very different requirements.

A more accurate sizing calculation uses:

simultaneous hot-water flow + required temperature rise

Example of Temperature Rise

If incoming water arrives at 65°F and you want 120°F hot water, the heater needs to raise it by 55°F.

If winter inlet water is only 40°F, the required rise becomes 80°F.

The second situation is much more demanding.

As a result, practical GPM may be significantly lower in colder climates.

Can It Supply 2 to 4 Fixtures at Once?

The manufacturer describes the heater as capable of supporting approximately 2 to 4 fixtures simultaneously.

That is possible in some scenarios, but fixture count is an imprecise measure.

A bathroom faucet and a shower do not consume the same amount of water.

Neither do a low-flow showerhead and a high-flow tub filler.

Add the Actual Flow Rates

Suppose a household uses:

• Shower: 2.0 GPM
• Second shower: 2.0 GPM
• Bathroom faucet: 1.0 GPM

That totals approximately 5.0 GPM.

This is close to the heater's stated maximum before accounting for temperature rise.

In cold-water conditions, that simultaneous demand may exceed practical capacity.

Better for Moderate Whole-House Demand

A 5.1 GPM unit may be a good fit for households where simultaneous hot-water demand is moderate.

Examples might include:

• One shower plus a faucet
• Two efficient showers
• Shower plus dishwasher

It may be less suitable for a home that regularly operates:

• Three showers simultaneously
• Large soaking tub filler plus shower
• Several high-flow fixtures together

In those cases, a higher-capacity model may be more appropriate.

Continuous Hot Water Within Capacity

One major benefit of tankless heating is that there is no fixed storage tank to empty.

As long as the unit has:

• Gas
• Electricity
• Adequate water flow
• Demand within its heating capacity

it can continue supplying hot water.

That can be useful for households with back-to-back showers.

Continuous Does Not Mean Unlimited

A tankless water heater can run continuously, but it cannot heat unlimited water at unlimited flow.

If demand exceeds the burner's ability to raise the water to the set temperature, the system may reduce output or fail to maintain the desired temperature.

Proper sizing prevents this problem.

Water-Flow Servo for Temperature Stability

The source states that the heater uses an advanced water-flow servo.

A water-flow servo helps regulate how much water passes through the heat exchanger so outlet temperature remains more stable as demand changes.

This is important because sudden changes in flow can otherwise produce noticeable temperature variation.

Claimed ±1°F Temperature Stability

Westinghouse claims temperature control within approximately ±1°F.

That can contribute to a more comfortable shower when other fixtures turn on or off.

Real-world performance will still depend on:

• Inlet water temperature
• Water pressure
• Gas pressure
• Installation
• Simultaneous fixture demand

The specification should therefore be treated as an operating target rather than a guarantee under every condition.

Smart App Control

The heater can be controlled through a smartphone app according to the supplied description.

This allows users to manage settings without standing directly in front of the appliance.

Depending on the implementation, app control may provide access to:

• Temperature settings
• Heater status
• Operating information
• Alerts

The exact functions should be confirmed for the current model and app version.

LED Control Panel

The unit also includes a physical LED interface.

The display is described as showing:

• Water temperature
• Operating status
• Error codes

A local control panel remains useful even on a WiFi-enabled appliance because it allows basic monitoring without a smartphone.

Error Codes Can Simplify Troubleshooting

Modern tankless heaters rely on multiple sensors.

If the unit detects an abnormal condition, an error code can help identify whether the problem relates to:

• Ignition
• Flow
• Venting
• Temperature
• Gas supply

The service manual should be used to interpret codes accurately.

Natural Gas Operation

This specific model uses natural gas.

That means it is intended for homes with an appropriate natural-gas supply.

A natural-gas model should not be connected to propane unless the manufacturer explicitly provides an approved conversion procedure.

Gas Supply Must Be Properly Sized

A 120,000 BTU appliance can place substantial demand on a home's gas system.

An existing line that worked with a conventional tank heater may not necessarily be adequate.

The installer should evaluate:

• Gas pipe diameter
• Pipe length
• Gas pressure
• Other connected appliances
• Meter capacity

Gas-Line Undersizing Can Cause Problems

If the gas supply cannot deliver enough fuel, the heater may experience:

• Poor combustion
• Reduced output
• Ignition issues
• Error codes

This is why tankless water heater installation should not be treated as a simple appliance swap.

Indoor Installation Only

The product is intended for indoor installation.

Indoor gas water heaters require appropriate combustion-air management and exhaust venting.

The exact vent configuration should follow the manufacturer's installation manual.

Variable-Speed Fan

The source mentions a precision variable-speed fan.

This fan helps manage combustion airflow and exhaust under changing burner loads.

That can contribute to stable operation across different hot-water demands.

Venting Is a Critical Safety Requirement

Gas combustion produces exhaust gases that must be vented safely outside.

An incorrectly installed vent can create serious health and safety risks.

Vent diameter, materials, length, termination location, and clearances all need to match the manufacturer's requirements and applicable codes.

CSA Certification

The unit is described as CSA certified.

Certification indicates that the product has been evaluated against applicable safety and performance standards associated with that listing.

Certification does not replace proper installation.

Freeze Protection

The heater includes a freeze protection system according to the source.

This is useful in colder environments, but built-in freeze protection should not be misunderstood.

The water heater and exposed piping can still freeze if conditions exceed the protection system's capabilities or electrical power is lost.

Protect Water Lines Too

Even if the appliance contains freeze-protection components, external plumbing can remain vulnerable.

Proper insulation and cold-weather installation practices are still necessary.

Tankless Heaters Still Need Electricity

Although the unit heats with natural gas, it depends on electricity for:

• Electronic controls
• Ignition
• Fan
• Sensors
• WiFi functions

During a power outage, most modern gas tankless water heaters cannot operate normally.

Standard 3/4-Inch NPT Connections

The heater uses standard 3/4-inch NPT plumbing connections according to the source.

This is common for residential tankless water heaters and helps support adequate water flow.

The installer should still confirm the required sizes for:

• Cold-water inlet
• Hot-water outlet
• Gas connection

from the current installation documentation.

Space-Saving Design

Tankless water heaters are wall-mounted and generally occupy far less floor area than conventional tank systems.

This can be valuable in:

• Utility rooms
• Mechanical closets
• Basements
• Garages

However, the appliance still requires clearance for service, venting, and pipe connections.

Smart Choice for Space-Constrained Homes

Replacing a large tank with a wall-mounted heater can free usable floor space.

That may be especially attractive in smaller homes or utility areas where every square foot matters.

Tankless vs. Traditional Tank Water Heater

The main difference is storage.

A conventional heater keeps a large volume of water hot.

A tankless heater heats water as needed.

Tankless Advantages

Potential benefits include:

• Continuous hot water within capacity
• Compact installation
• Reduced standby heating

Storage Tank Advantages

Potential benefits include:

• Simpler installation
• Stored reserve for short periods of high demand
• Less dependence on high instantaneous gas input

Neither design is automatically better for every home.

Hot Water Still Takes Time to Reach the Faucet

Tankless heating does not eliminate the water already sitting inside household pipes.

If a bathroom is far from the water heater, users may still wait for hot water to travel through the plumbing.

That delay depends on:

• Pipe length
• Pipe diameter
• Flow rate

rather than whether the heater has a tank.

Recirculation Considerations

If long hot-water wait times are a problem, a recirculation system may help.

The supplied product description does not mention a built-in recirculation pump.

Homeowners who want near-immediate hot water at distant fixtures should verify whether external recirculation options are compatible.

Hard Water and Scale

Tankless heat exchangers can accumulate mineral deposits.

Hard-water scale can reduce heat-transfer efficiency and restrict flow.

Homes with mineral-rich water may need periodic descaling.

Maintenance Is Important

A tankless heater is not maintenance-free.

Depending on water quality and manufacturer recommendations, routine care may include:

• Flushing heat exchanger
• Cleaning inlet filter
• Inspecting venting
• Checking connections

Maintenance helps preserve efficiency and reduce long-term problems.

Service Valves Are Worth Considering

A tankless service-valve kit can simplify future heat-exchanger flushing.

If one is not included, ask the installer whether it should be added during installation.

Doing so is easier than modifying the plumbing later.

Warranty Coverage

The supplied information states:

2-year warranty for the complete unit

and

5-year warranty for the heat exchanger

The heat exchanger is a major component, so the longer coverage is noteworthy.

Review the complete warranty because coverage may depend on:

• Correct installation
• Maintenance
• Registration
• Water quality

Professional Installation Is Recommended

This product involves:

• Natural gas
• Combustion
• Exhaust venting
• Plumbing
• Electricity

Professional installation is strongly advisable.

A qualified installer can verify both performance and safety requirements.

Common Sizing Mistakes

Choosing by the 5.1 GPM Number Alone

The actual capacity depends on temperature rise.

Counting Fixtures Instead of Flow

Four faucets are not equivalent to four showers.

Ignoring Winter Inlet Temperature

Cold incoming water can substantially reduce practical flow.

Forgetting Gas-Line Capacity

A 120,000 BTU heater may require plumbing changes.

Assuming Tankless Means Instant Hot Water

There is still a travel delay through household piping.

Who Is This Heater Best For?

This Westinghouse model may be a good fit for:

• Small to medium households
• Homes with moderate simultaneous hot-water demand
• Properties with natural gas
• Owners who want app control
• Homes where wall-mounted installation saves useful space

It may be especially suitable when one or two showers are the largest simultaneous demands.

Who May Need a Larger Model?

A higher-output heater may be more appropriate for homes with:

• Multiple simultaneous showers
• Large soaking tubs
• High-flow fixtures
• Very cold inlet water

Sizing should be based on peak flow and temperature rise rather than brand or household size alone.

Advantages and Considerations

Advantages

• 120,000 BTU natural-gas burner
• Up to 5.1 GPM stated maximum flow
• Whole-home capability for moderate demand
• Smartphone app control
• LED display
• Water-flow servo
• Claimed ±1°F temperature stability
• Variable-speed combustion fan
• Freeze protection
• CSA certification
• Standard 3/4-inch NPT connections
• 5-year heat-exchanger warranty

Potential Considerations

• Maximum 5.1 GPM is condition dependent
• May be undersized for heavy simultaneous use
• Professional gas and vent installation is recommended
• Gas line may require upgrading
• Electricity is still required
• Hard water can cause scale
• Indoor installation only

Frequently Asked Questions

What fuel does this water heater use?

Natural gas.

What is its maximum burner input?

Approximately 120,000 BTU, according to the supplied information.

What is the maximum flow rate?

Up to 5.1 GPM under appropriate conditions.

Will it always provide 5.1 GPM?

No. Actual output depends heavily on the required temperature rise.

Can it supply multiple fixtures?

Yes, potentially. The manufacturer describes support for approximately 2 to 4 fixtures, but combined flow is the better sizing method.

Can it run two showers?

Possibly, especially with efficient showerheads and moderate inlet-water temperatures. Actual capability depends on total flow and temperature rise.

Does it have WiFi control?

Yes.

Can I adjust it from a phone?

Yes, according to the supplied product information.

Is there a physical display?

Yes. An LED panel displays temperature, status, and error information.

How stable is the water temperature?

The source claims regulation within approximately ±1°F.

Does it include freeze protection?

Yes.

Is it CSA certified?

Yes, according to the supplied information.

What plumbing connections does it use?

The source lists 3/4-inch NPT connections.

Is it designed for outdoor installation?

No. This model is described as indoor only.

Does a gas tankless water heater need electricity?

Yes. Electricity powers the controls, ignition, fan, and other systems.

Does it require professional installation?

Professional installation is strongly recommended because gas supply, venting, plumbing, and electrical requirements must all be correct.

What is the warranty?

The source lists 2 years for the complete unit and 5 years for the heat exchanger.

Final Thoughts

The Westinghouse 120,000 BTU 5.1 GPM natural gas tankless water heater is designed for homeowners who want a compact whole-house hot-water system with smart controls and enough capacity for moderate simultaneous demand.

Its strongest features are the on-demand natural-gas heating system, up to 5.1 GPM rated flow, app-based control, LED monitoring, water-flow servo, freeze protection, and CSA certification.

The main consideration is sizing. A 5.1 GPM rating can be sufficient for many households, but actual output depends heavily on incoming water temperature and the number and type of fixtures running at once. Gas-line capacity and venting also need to be evaluated before installation.

For a home with moderate hot-water demand, natural-gas service, and a preference for WiFi-enabled controls, this Westinghouse model offers a practical middle ground between compact point-of-use units and larger high-output tankless systems.