Buying guide · 10 min read · Updated October 2, 2026

4 Best 42000 Btu RV Tankless Water Heater in 2026: A Practical RV Guide

Best 42,000 BTU RV tankless water heaters compared on controls, safety features, door fit and low-flow ignition for travel trailers and motorhomes.

By Bowen HigginsRV Editor at RV Gear Lab4 products comparedSpec-sheet researched

A 42,000 BTU tankless heater is the entry rung of propane on-demand hot water, so the buying question is less about raw output and more about how each unit protects itself, how it fits your door and how low a flow it will light at. This shortlist compares four 42,000 BTU models on those points.

Each heater was read for what its own listing states: BTU, door sizes, temperature range, minimum flow and safety features. Headline flow numbers depend on inlet and outlet temperatures, so none are quoted as promises here.

RV Gear Lab field notes

The Rig Fit Check

Start with the job: Suburban ST-42 42 leads this shortlist for Families wanting scald and child safeguards. Use that fit as a reference point, then compare the alternatives against your own space and workload.
Specs that separate the picks: The first details to compare are Flame out protection, 12V under 3 amps, 42,000 BTU gas heater. Confirm the exact model and included components before ordering.
Trade-off to plan for: Pricier than Garvee 42,000

Before you buy

What Matters Before You Choose a 42000 Btu RV Tankless Water Heater

Key buying criteria so you get the right fit the first time.

01
What 42,000 BTU delivers
BTU is fuel input per hour, and it sets how much temperature rise you can get at a given flow. It matters because a showering family needs enough rise on cold inlet water. Treat any gpm figure as dependent on inlet and outlet temperature.
02
Minimum ignition flow
A tankless burner needs a minimum flow to fire, and low-flow faucets can fall below it. It matters for quiet, trickle use. Look for a stated minimum such as 0.74 GPM.
03
12V control power
Most propane tankless units still need 12V for the fan, controller and ignition. It matters when boondocking on batteries. Check the listed amp draw, such as under three amps.
04
Door and cutout fit
Tankless heaters come with different door sizes, such as 15 by 15 or 18 by 18 inches. It matters because a mismatch means cutting or a trim kit. Measure the opening.
05
Safety features
Flame out, scald and freeze protections help avoid injury and damage. It matters most with children or winter use. Look at the safety list on the listing.

Our standards

Why You Can Trust RV Gear Lab

At RV Gear Lab, we compare products based on rig fit and power or hookup compatibility, verified specifications, usability, setup requirements, weight, durability, and real-world trade-offs. We do not rank products purely on marketing claims or commission rates.

We have not personally tested every product listed. Where hands-on testing is not available, recommendations are based on verified manufacturer specifications, product documentation, use-case fit, and comparative research.

How we review RV gear →

Detailed reviews

The 4 best 42000 btu rv tankless water heater, explained

Best Safety Feature Set · 1 of 4

Suburban ST-42 42

Flame out protection
Scald kill switch and child lock
Freeze and voltage protection

Check price on Amazon

Best for: Families wanting scald and child safeguards

Our take

Best for families who want child lock and scald protection.

Why it made the shortlist

The Suburban ST-42 is a 42,000 BTU tankless heater whose listing details flame out protection, an internal high-temperature scald kill switch and a child lock that holds outlet temperature to 113 F. It also lists active freeze protection and voltage protection.

Compared with the Garvee and RecPro units, it is the best documented on family-oriented safeguards, and it comes from a long-standing RV water heater maker.

It also suits buyers who prefer a familiar brand.

What works

Child lock holds outlet at 113 F
Scald protection kill switch
Flame out protection
Freeze protection listed

Watch out for

Pricier than Garvee 42,000
Needs 12V control power

Check price on Amazon

Best Quiet Digital Control · 2 of 4

GIRARD Tankless RV Water Heater

12V under 3 amps
Microprocessor temperature control
95 to 124 F digital panel

Check price on Amazon

Best for: Quiet, steady-temperature buyers

Our take

A great fit for travelers who want steady temperature and fuel savings.

Why it made the shortlist

The GIRARD tankless RV water heater is a 42,000 BTU unit with a quiet brushless motor that runs on 12V power under three amps. An onboard microprocessor monitors incoming temperature, flow and outgoing temperature to keep output steady.

It adds a digital control panel with 95 to 124 F adjustment and a Fahrenheit and Celsius toggle. The listing says it uses half the LP gas of a six-gallon tank heater for the same hot water.

It also suits owners who value low noise.

What works

Quiet brushless motor
Microprocessor holds steady temperature
Digital panel with Fahrenheit and Celsius
Claims half the LP gas of a six-gallon tank

Watch out for

Professional installation is recommended

Check price on Amazon

Best Choice of Door Sizes · 3 of 4

RecPro RV Tankless Gas Water Heater

42,000 BTU gas heater
15 or 18 inch door sizes
Copper heat exchanger

Check price on Amazon

Best for: Buyers with specific door sizes

Our take

Best for owners who need the 18 inch door option or want fault codes.

Why it made the shortlist

The RecPro RV Tankless Gas Water Heater is a 42,000 BTU unit offered in two door sizes, 15 by 15 inch or 18 by 18 inch. It has a copper heat exchanger, automatic ignition and low water pressure startup.

It adds wired controllers with fault auto-diagnosis and code display, a speed-changing function for different flow rates and wind resistance for outdoor use. Choosing the door size that matches your cutout keeps the install simple.

It also suits those replacing an older tank heater.

What works

Two door size options
Copper heat exchanger
Fault auto-diagnosis with code display
Wind resistance function

Watch out for

Wired controllers add wiring work
Choose door size carefully

Check price on Amazon

Best Value Tankless · 4 of 4

Garvee RV Tankless Water Heater

Six safety features
Ignition at 0.74 GPM
14.5 to 100 psi range

Check price on Amazon

Best for: Budget tankless buyers

Our take

A strong pick for budget upgrades from a tank heater.

Why it made the shortlist

Garvee's 42,000 BTU model offers low-flow ignition at a minimum of 0.74 GPM and a water pressure range of 14.5 to 100 psi. It lists six safety features: overheat protection, overpressure relief, flame failure protection, anti-freeze protection, flue blockage protection and an ignition failure alarm.

It costs well below the Suburban ST-42 and still adds an anti-freeze function that starts below 42 F. Temperature adjusts from 95 to 123 F.

It also suits anyone who wants the longest safety list at the lowest price.

What works

Ignition at 0.74 GPM minimum flow
Six safety features listed
Anti-freeze function below 42 F

Watch out for

Less brand history than Suburban
Needs 12V power supply

Check price on Amazon

Methodology

How We Built This Shortlist

Each pick was assessed across 4 criteria weighted for real-world use.

42,000 BTU match

Only units whose listing states 42,000 BTU were credited.

Safety and controls

Child lock, scald, flame and freeze protections were compared.

Fit

Door sizes and plumbing connections were noted.

Flow

Minimum ignition flow and pressure range were weighed.

Decision guide

Match a 42000 Btu RV Tankless Water Heater to Your RV

By what matters most

Your situation	Recommended pick	Why
Child and scald safeguards	Suburban ST-42	Child lock and scald kill switch
Quiet, steady temperature	GIRARD 42,000	Quiet motor and microprocessor
18 inch door	RecPro 42,000	Choice of 15 or 18 inch door
Lowest price	Garvee 42,000	Six safeties at a lower price

By Budget

Budget	Recommended pick
$230 to $410	Garvee 42,000 or Suburban ST-42
$440 to $490	GIRARD 42,000 or RecPro 42,000

Brand-name vs budget tankless

Brand-name

The Suburban ST-42 and GIRARD 42,000 come from established RV heater makers with detailed controls.

Budget

The Garvee 42,000 and RecPro 42,000 cost less and add flexible fit and safeties.

Most buyers should choose the Garvee 42,000 unless child-lock safeguards matter.

By your install

Install	Recommended pick
Standard 15 inch door	RecPro 42,000
Family with kids	Suburban ST-42
Boondocking on batteries	GIRARD 42,000
Budget swap	Garvee 42,000

For Boondocking Specifically

Look for

low 12V draw and a quiet fan

In this comparison

The GIRARD 42,000 states 12V under three amps and the Garvee 42,000 ignites at 0.74 GPM.

When to Spend More

Spend more if

Spend more if you want family safeguards: the Suburban ST-42 offers child lock and scald protection.

Save if

Save if you want a simple upgrade: the Garvee 42,000 costs well below the Suburban ST-42 and lists six safeties.

FAQ

Before You Bring One Home

Does a 42,000 BTU tankless heater need 12V power?

Most units do, for the fan, controller and ignition. The GIRARD 42,000 lists under three amps, so check each model before boondocking.

What mistake do people make?

Trusting a headline gpm without the temperature rise behind it. Judge by BTU, minimum flow and your inlet temperature.

Is the Suburban ST-42 worth it over the Garvee 42,000?

If you want child lock and scald protection from a known brand, yes. For basic needs the Garvee 42,000 is cheaper.

How do I install a tankless heater?

Shut off propane and power, remove the old unit, connect 1/2 inch water and gas lines and test for leaks. Professional installation is recommended in some listings.

How do I protect it in winter?

Use the freeze protection if listed and drain the unit when storing. Active freeze protection needs power and propane.

Bottom line

The short version

Best Safety Feature Set
Suburban ST-42 42
Check price for Suburban ST-42 42 (opens in a new tab)
Best Quiet Digital Control
GIRARD Tankless RV Water Heater
Check price for GIRARD Tankless RV Water Heater (opens in a new tab)
Best Choice of Door Sizes
RecPro RV Tankless Gas Water Heater
Check price for RecPro RV Tankless Gas Water Heater (opens in a new tab)
Best Value Tankless
Garvee RV Tankless Water Heater
Check price for Garvee RV Tankless Water Heater (opens in a new tab)

Browse more 42000 btu rv tankless water heater on Amazon →

About the author

Bowen Higgins

RV Editor at RV Gear Lab

Bowen covers RV power, water systems, towing and leveling, upkeep and interior comfort, with a focus on matching gear to the rig, the hookups and the way you actually travel.

4 Best 42000 Btu RV Tankless Water Heater in 2026: A Practical RV Guide

Our top picks

The Rig Fit Check

What Matters Before You Choose a 42000 Btu RV Tankless Water Heater

What 42,000 BTU delivers

Minimum ignition flow

12V control power

Door and cutout fit

Safety features

Why You Can Trust RV Gear Lab

The 4 best 42000 btu rv tankless water heater, explained

Suburban ST-42 42

GIRARD Tankless RV Water Heater

RecPro RV Tankless Gas Water Heater

Garvee RV Tankless Water Heater

How We Built This Shortlist

42,000 BTU match

Safety and controls

Fit

Flow

Match a 42000 Btu RV Tankless Water Heater to Your RV

By what matters most

By Budget

Brand-name vs budget tankless

By your install

For Boondocking Specifically

When to Spend More

Before You Bring One Home

Does a 42,000 BTU tankless heater need 12V power?

What mistake do people make?

Is the Suburban ST-42 worth it over the Garvee 42,000?

How do I install a tankless heater?

How do I protect it in winter?

The short version

Bowen Higgins

Related guides