11 Easy Install Propane Tankless Heater For Existing Plumbing Connections of 2026 Without Repiping

1

Rheem RTG-84DVLP-3 High Efficiency Non-Condensing Indoor Tankless Liquid Propane Water

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  9.6
• Brand
  Rheem

Key specs2

Hot Water Capacity

8.4 GPM (180,000 BTU/hr)

Warranty Coverage

Includes a 15-year warranty on the heat exchanger alongside a 5-year parts warranty for indoor residential setups.

Pros & cons43

Pros

• Delivers up to 8.4 GPM and 180,000 BTU/hr to supply 3 to 4 fixtures simultaneously
• Features a 0.82 Uniform Energy Factor to cut energy costs over conventional tanks
• Digital LED panel allows temperature adjustments in exact 1-degree increments
• Backed by a 15-year heat exchanger warranty and a 5-year parts warranty

Cons

• Manufacturer specifies professional installation rather than a direct homeowner setup
• Listing does not specify water or gas port NPT sizes, requiring verification before connecting
• Weighs 46.5 pounds, making it heavier than most compact indoor models

2

ThermoMate CZ422LP, 102,000 BTU 4.7 GPM Propane Tankless Water Heater

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  9.3
• Brand
  thermomate

Key specs2

Plumbing Connection Sizes

• Water inlet and outlet: 3/4-inch NPT
• Gas inlet: 1/2-inch NPT
• Vent connection: 3-inch outer diameter

Power and Vent Setup

Plugs into standard 120V wall outlets with an included 5-foot cord and routes exhaust through a 3-inch OD vent connection.

Pros & cons42

Pros

• Uses standard 3/4-inch NPT water ports and a 1/2-inch NPT gas inlet for direct plumbing fits
• Connects directly to standard 120V outlets with an included 5-foot UL-certified power cord
• Provides built-in frost protection via 4 ceramic cores that activate automatically at 41 degrees Fahrenheit
• 3.5-inch LED diagnostic screen shows real-time flow rate, fan status, and error codes

Cons

• Requires a dedicated 3-inch outer diameter exhaust vent penetration through the wall
• Maximum heating output of 113,000 BTU limits simultaneous use to two showers in colder climates

3

Propane Tankless Water Heater, 4.74 GPM 18L Indoor, Instant Hot

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  9.1
• Brand
  forimo

Key specs2

Port Thread Specifications

• Cold water inlet: 1/2-inch NPT
• Hot water outlet: 1/2-inch NPT
• Gas inlet: 1/2-inch NPT

Exhaust Vent Size

2.3-inch (6 cm) diameter vent pipe

Pros & cons42

Pros

• Features matching 1/2-inch NPT connections across water inlet, outlet, and gas line
• Includes a compact 2.3-inch (6 cm) exhaust pipe diameter for smaller wall vent holes
• Delivers up to 4.74 GPM and 123,000 BTU/hr for two to three simultaneous fixtures
• Operates without an expansion tank at water pressures starting at 29 PSI

Cons

• All 1/2-inch NPT ports will require adapters if your existing plumbing uses 3/4-inch lines
• Requires manual draining via the pressure relief valve during freezing weather when idle

4

Westinghouse Tankless Water Heater Propane Indoor, 7.9 GPM 180,000 BTU

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  8.9
• Brand
  Westinghouse

Key specs2

Smart Controls

Features integrated WiFi connectivity and voice control for remote temperature adjustments and real-time fault tracking.

Plumbing Compatibility

Standard 3/4-inch NPT water connections

Pros & cons42

Pros

• Matches existing residential 3/4-inch NPT plumbing connections directly
• Generates 180,000 BTU and up to 7.9 GPM to supply 3 to 5 fixtures at once
• Built-in WiFi and voice control allow temperature changes without touching the unit
• Plugs into existing 120V AC electrical supply with self-modulating gas burners

Cons

• Vent pipe diameter and clearance specs are omitted from the listing and require verification
• Product description contains conflicting mentions of indoor and outdoor installation

5

Ranein Propane Gas Tankless Water Heater, 8.5 GPM, 190,000 BTU,

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  7.8
• Brand
  Ranein

Key specs2

High Elevation Limit

Not recommended above 2,000 feet

Combustion Fan Placement

Bottom-mounted blower actively prevents exhaust backflow while varying speed against exterior wind pressure.

Pros & cons43

Pros

• Utilizes standard 3/4-inch NPT water fittings for straightforward pipe alignment
• Provides high 190,000 BTU output and 8.5 GPM flow for 4 to 6 simultaneous outlets
• Bottom-mounted combustion blower prevents exhaust backdraft and adjusts fan speed automatically
• Compact 8.07-inch depth fits tight utility closets and mechanical spaces

Cons

• Not recommended for elevations above 2,000 feet due to oxygen and combustion limits
• Listing does not specify the gas inlet thread size or exhaust vent pipe diameter
• Requires manual draining via the pressure relief valve when left unheated in freezing weather

6

Heatrova Propane Gas Tankless Water Heater, 4.3 GPM, 102,000 BTU,

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  7.8
• Brand
  Heatrova

Key specs2

Line and Vent Dimensions

• Water connections: 3/4-inch NPT
• Gas inlet connection: 3/4-inch NPT
• Exhaust vent: 3-inch diameter

Cold Weather Activation

Built-in heaters engage automatically below 39°F

Pros & cons42

Pros

• Uses matching 3/4-inch NPT connections for both water lines and the gas supply inlet
• Automatic freeze protection engages built-in heating modules when ambient temps drop below 39 degrees
• Connects directly to a 3-inch exhaust vent and standard UL-approved 120V electrical outlet
• Slim 6.8-inch depth and 21.3-inch height conserve space on utility room walls

Cons

• 4.3 GPM maximum capacity may bottleneck if multiple high-flow showers run together in winter
• Pure copper heat exchanger requires regular descaling in hard water environments to maintain efficiency

7

GASLAND Gasmart E Propane Tankless Gas Water Heater Indoor, Max

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  7.7
• Brand
  GASLAND

Key specs2

Energy Rating and Output

199,000 BTU/hr with 0.80 UEF

Installation Verification Needs

Port thread sizes and vent diameter are omitted from manufacturer specs, so verify fittings before mounting.

Pros & cons42

Pros

• Generates 199,000 BTU to deliver up to 7.6 GPM for whole-home simultaneous demands
• High 0.80 Uniform Energy Factor cuts fuel consumption compared to standard gas tanks
• Certified by CSA with integrated freeze, flame-out, and overheat protection sensors
• Includes a 1-year replacement warranty supported by U.S.-based customer service

Cons

• Specific NPT connection sizes for gas and water lines are not listed and must be confirmed
• Exhaust vent pipe diameter and power supply specs are omitted from the listing

8

18L Tankless Water Heater Propane with Digital Display 4.76 GPM

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  7.4
• Brand
  Baococo

Key specs2

Operating Environment

Outdoor and portable RV use only

Water Temperature Span

Adjustable from 17°F to 113°F

Pros & cons43

Pros

• Delivers up to 4.76 GPM and 115,425 BTU/hr without requiring hardwired electrical connections
• Includes a handheld shower head featuring an integrated one-button shutoff to stop water flow
• Features six safety cutoffs including low-flow ignition lockout and dry combustion prevention
• Compact 12.6-inch square footprint is easy to mount in outdoor or cabin setups

Cons

• Designed for outdoor or portable use and is not rated for indoor home plumbing installations
• Listing omits NPT pipe fitting sizes, requiring adapters for standard residential lines
• Maximum water temperature tops out at 113 degrees Fahrenheit

9

Novieex Propane Gas Tankless Water Heater Up to 4.3 GPM

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  7.2
• Brand
  NOVIEEX

Key specs2

Water Pressure Threshold

Operational from 1.5 to 116 PSI

Uniform 1/2-inch Ports

• Cold water inlet: 1/2-inch NPT
• Hot water outlet: 1/2-inch NPT
• Gas supply line: 1/2-inch NPT

Pros & cons42

Pros

• Direct 1/2-inch NPT threading across cold inlet, hot outlet, and propane gas connection
• Operates on standard 110V to 120V AC household outlets at low water pressure down to 1.5 PSI
• Wide temperature selection range between 95 and 149 degrees Fahrenheit via LED touchscreen
• Lightweight 19.84-pound frame simplifies single-person mounting on wall studs

Cons

• Requires reducer adapters if connecting to existing 3/4-inch residential plumbing lines
• Exhaust vent pipe diameter and venting hardware specifications are not provided

10

Tankless water heater Gas Propane 1.6GPM VENT FREE 41000 BTU

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  7.2
• Brand
  MAWI

Key specs2

Outdoor Vent-Free Setup

Operates outdoors without an exhaust flue or wall thimble, relying on open-air ventilation.

Flow and BTU Rating

1.6 GPM flow at 41,000 BTU/hr

Pros & cons33

Pros

• Vent-free outdoor design eliminates the need to cut wall penetrations or run exhaust flues
• Three mechanical dials provide independent control over gas flow, water volume, and temperature
• Ultra-compact 11.2-inch footprint fits easily on outdoor cabin walls and camper mounts

Cons

• Strictly restricted to outdoor installation and must never be installed inside living quarters
• Low 1.6 GPM flow and 41,000 BTU capacity can only support a single point of use at a time
• Plumbing connection sizes are not specified, requiring confirmation prior to hookup

11

Tankless Water Heater Instant Propane Gas Water Heater 14L 3.66GPM

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  7.1
• Brand
  Baococo

Key specs2

Minimum Water Pressure

Ignites at 3.6 PSI (up to 116 PSI)

Off-Grid Utility

Engineered for outdoor cabin and RV washing tasks with an included shutoff shower head and 85,300 BTU burner.

Pros & cons43

Pros

• Low-flow ignition system activates reliably at water pressures as low as 3.6 PSI
• Integrated 10 percent energy-saving mode limits propane usage during temporary outdoor sessions
• Delivers 3.66 GPM flow and 85,300 BTU/h output for off-grid cabins and RV use
• Six integrated safety protections shut off fuel automatically during flame failure or dry firing

Cons

• Rated strictly for outdoor use and cannot be connected to indoor closed plumbing systems
• Water temperature adjustment is capped at a maximum of 113 degrees Fahrenheit
• Pipe connection sizes are omitted from product data and require checking before purchase

Last update on 2026-10-11 / Affiliate links / Images, Product Titles, and Product Highlights from Amazon Product Advertising API

Will a propane tankless water heater thread directly onto existing 1/2-inch or 3/4-inch plumbing lines?

It depends on the specific port dimensions of the unit, so you must verify whether the heater uses 1/2-inch or 3/4-inch NPT fittings before mounting. Certain models, such as the Novieex 4.3 GPM heater, feature NPT 1/2-inch gas inlets, cold water inlets, and hot water outlets designed to match 1/2-inch runs directly. Other units, including the Heatrova 102,000 BTU model, come with 3/4-inch NPT connections. Selecting a unit that matches your existing pipe sizing allows you to thread directly onto your current plumbing connections without adding step-down adapters or soldering new copper joints.

How do you confirm your propane supply line provides enough volume for a tankless unit?

You must check the heater heating demand against the diameter and pressure of your current gas line. Demands vary significantly across models, from 100,000 BTU on the Novieex or 102,000 BTU on the Heatrova up to 190,000 BTU on the Ranein and 199,000 BTU on the GASLAND Gasmart E. Also, verify that your regulator delivers the required operating pressure, such as the 11.24 inches water column (2.8 kPa) gas rated pressure specified for the Novieex. If an existing supply line was sized only for a low-demand tank heater, it may restrict propane volume during peak demand and cause the burner to shut down.

Can you route the exhaust through an existing vent opening?

You can only reuse an existing exhaust opening if the vent pipe diameter, duct routing, and fan requirements match the manufacturer specifications. Many modern indoor units use forced exhaust, such as the Ranein heater with bottom-mounted fans that automatically adjust rotating speed to push combustion gases out and prevent smoke backflow. Outdoor or portable options, such as the MAWI 41,000 BTU heater, are vent-free and must not be used indoors without approved exterior airflow. If you are comparing indoor ventilation setups, review guidelines for a propane heater with safe indoor venting to confirm clearance rules before cutting or reusing wall openings.

Do propane tankless heaters require a standard electrical outlet near existing plumbing?

Yes, indoor propane tankless units typically require a dedicated electrical connection to power their control boards, digital temperature displays, and exhaust fans. The Novieex 4.3 GPM heater, for example, lists an electrical requirement of 110V to 120V AC at 60Hz. If your previous water heater used a standing pilot light without electrical wiring, you will need a standard 120V outlet located close to your plumbing lines. Homeowners who prefer to avoid electrical modifications altogether often weigh other utility configurations, including an electric tankless water heater to match panel capacity, before finalizing their mechanical room layout.

What built-in safety protections prevent damage to existing household pipes?

Look for units with integrated freeze protection and flow-monitoring safeguards to prevent ruptured plumbing and heat exchanger failure. The ThermoMate CZ422LP is CSA certified and includes eight built-in protections, covering boil-dry, freeze, flame-out, overheating, over-temperature, and pipe blockage. Other indoor units provide flame failure devices alongside anti-freezing protection to safeguard against unburned fuel and cold snaps. These internal sensors monitor operating conditions continuously, shutting down the gas valve automatically if water flow drops or internal temperatures exceed safe operating thresholds.

How much wall space is required when replacing a storage tank with a tankless model?

Propane tankless units mount flat against wall studs and take up a fraction of the floor space used by a 50-gallon storage tank, but you must confirm cabinet dimensions to ensure adequate clearance around your existing pipe drops. Compact options like the Heatrova measure 13.7 by 13.7 by 13.7 inches, while mid-sized units like the ThermoMate measure 13.77 by 13.77 by 21.65 inches with a weight of 22 pounds. Higher-output whole-home models, like the Rheem RTG-84DVLP-3, require 10.27 by 13.5 by 24.2 inches of vertical clearance and weigh 46.5 pounds. Measuring your wall space beforehand ensures water valves and gas shutoffs remain fully accessible after installation.