Buying Guide
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 Hardcastle's RV Editors
10 min read4 products evaluated
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.
Hardcastle’s RV field notes
The Rig Fit Check
A quick way to connect the shortlist to the space, workload and ownership details that matter after the box arrives.
- 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
The Practical Shortlist
A road-tested-thinking look at 4 options, organized around the job each one suits best.
Best Safety Feature Set
Suburban ST-42 42
Families wanting scald and child safeguards
Our take Check price for Suburban ST-42 42 (opens in a new tab)
Best Quiet Digital Control
GIRARD Tankless RV Water Heater
Quiet, steady-temperature buyers
Our take Check price for GIRARD Tankless RV Water Heater (opens in a new tab)
Best Choice of Door Sizes
RecPro RV Tankless Gas Water Heater
Buyers with specific door sizes
Our take Check price for RecPro RV Tankless Gas Water Heater (opens in a new tab)
Best Value Tankless
Garvee RV Tankless Water Heater
Budget tankless buyers
Our take Check price for Garvee RV Tankless Water Heater (opens in a new tab)
| Pick | Best for | Key spec | Price |
|---|---|---|---|
| Families wanting scald and child safeguards | Flame out protection | Check price for Suburban ST-42 42 (opens in a new tab) |
| Quiet, steady-temperature buyers | 12V under 3 amps | Check price for GIRARD Tankless RV Water Heater (opens in a new tab) |
| Buyers with specific door sizes | 42,000 BTU gas heater | Check price for RecPro RV Tankless Gas Water Heater (opens in a new tab) |
| Budget tankless buyers | Six safety features | Check price for Garvee RV Tankless Water Heater (opens in a new tab) |
Why Each Pick Made the Cut
Best Safety Feature Set1 of 4
Suburban ST-42 42 on Amazon (opens in a new tab)
Suburban ST-42 42 makes the shortlist because child lock holds outlet at 113 F.
Best for
- Families wanting scald and child safeguards
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.
Best for families who want child lock and scald protection. It also suits buyers who prefer a familiar brand.
Key dimensions & specs
- Flame out protection
- Scald kill switch and child lock
- Freeze and voltage protection
Pros
- Child lock holds outlet at 113 F
- Scald protection kill switch
- Flame out protection
- Freeze protection listed
Cons
- Pricier than Garvee 42,000
- Needs 12V control power
Best Quiet Digital Control2 of 4
GIRARD Tankless RV Water Heater on Amazon (opens in a new tab)
The strongest case for GIRARD Tankless RV Water Heater is quiet brushless motor.
Best for
- Quiet, steady-temperature buyers
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.
A great fit for travelers who want steady temperature and fuel savings. It also suits owners who value low noise.
Key dimensions & specs
- 12V under 3 amps
- Microprocessor temperature control
- 95 to 124 F digital panel
Pros
- Quiet brushless motor
- Microprocessor holds steady temperature
- Digital panel with Fahrenheit and Celsius
- Claims half the LP gas of a six-gallon tank
Cons
- Professional installation is recommended
Best Choice of Door Sizes3 of 4
RecPro RV Tankless Gas Water Heater on Amazon (opens in a new tab)
RecPro RV Tankless Gas Water Heater is the better fit when buyers with specific door sizes.
Best for
- Buyers with specific door sizes
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.
Best for owners who need the 18 inch door option or want fault codes. It also suits those replacing an older tank heater.
Key dimensions & specs
- 42,000 BTU gas heater
- 15 or 18 inch door sizes
- Copper heat exchanger
Pros
- Two door size options
- Copper heat exchanger
- Fault auto-diagnosis with code display
- Wind resistance function
Cons
- Wired controllers add wiring work
- Choose door size carefully
Best Value Tankless4 of 4
Garvee RV Tankless Water Heater on Amazon (opens in a new tab)
Choose Garvee RV Tankless Water Heater for ignition at 0.74 GPM minimum flow.
Best for
- Budget tankless buyers
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.
A strong pick for budget upgrades from a tank heater. It also suits anyone who wants the longest safety list at the lowest price.
Key dimensions & specs
- Six safety features
- Ignition at 0.74 GPM
- 14.5 to 100 psi range
Pros
- Ignition at 0.74 GPM minimum flow
- Six safety features listed
- Anti-freeze function below 42 F
Cons
- Less brand history than Suburban
- Needs 12V power supply
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.
What Matters Before You Choose a 42000 Btu RV Tankless Water Heater
Key buying criteria so you get the right fit the first time.
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.
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.
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.
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.
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.
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 |
Scroll sideways to see every column.
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.
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
Best overall: Suburban ST-42 42 — best safety feature set pick in this roundup. See the full verdicts above for every pick, with pros, cons and who each one suits.
Browse all 42000 btu rv tankless water heater on Amazon — Prime-eligible options with current pricing.