12 Best Continuous Hot Water Heater of 2026 For Endless Showers

1

Rheem RTG-84XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water

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  9.7
• Brand
  Rheem

Key specs2

Simultaneous Fixture Capacity

3 to 4 showers at 8.4 GPM (35°F rise)

Venting Requirements

Designed strictly for exterior wall mounting, this unit exhausts directly into the surrounding outdoor air, removing the expense and labor of routing direct-vent piping through your roof.

Pros & cons42

Pros

• Delivers up to 8.4 GPM at a 35°F temperature rise to run 3 to 4 showers at once
• Outdoor wall-mount installation eliminates indoor exhaust venting requirements
• Includes a digital LED control panel for water temperature adjustments in 1°F steps
• Features a 180,000 BTU burner and built-in freeze and flame failure protection

Cons

• Outdoor-only installation is not suitable for unvented interior utility closets
• Lacks integrated WiFi connectivity for mobile app control

2

110V Tankless Water Heater Electric, 3000W Tankless Electric Water Heater

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  9.6
• Brand
  xwdzswgs

Key specs2

Handwashing Flow Rate

0.3 to 0.5 GPM

Electrical Connection Specs

Requires dedicated wiring with a cross-sectional area of at least 2.5 square millimeters and a breaker rated over 32A, positioned strictly in a vertical orientation.

Pros & cons42

Pros

• Compact 4.32-inch profile fits easily into tight under-sink cabinet spaces
• Operates on standard 110V electrical power for point-of-use handwashing
• Provides 98% thermal efficiency with built-in dry boil and leakage protection
• Digital LCD screen displays current operating temperature and status

Cons

• Flow rate of 0.3 to 0.5 GPM cannot support household shower demands
• Requires vertical mounting and dedicated wiring with a breaker over 32A

3

ORBEK RV Tankless Water Heater, Propane, 12V DC, For RV

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  9.5
• Brand
  Orbek

Key specs2

High-Altitude Capability

Rated up to 9,800 ft elevation

RV Cutout Dimensions

Fits standard RV openings measuring 15x15, 15x18, or 18x18 inches using standard NPT water lines and a 12V DC camper battery system.

Pros & cons42

Pros

• Supplies on-demand hot water using a 60,000 BTU propane burner and 12V DC power
• Staged combustion and brushless DC fan maintain heating up to 9,800 feet of altitude
• Integrated 150 PSI pressure-reducing valve prevents plumbing overpressure
• Digital wired remote control provides temperature adjustments from 95°F to 123°F

Cons

• Exterior replacement door panels for 15x15 or 15x18 openings must be purchased separately
• Limited to single-fixture mobile applications rather than multi-bath homes

4

Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water

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  9.3
• Brand
  Rheem

Key specs2

Simultaneous Fixture Capacity

2 to 3 showers at 7.0 GPM (35°F rise)

Energy Efficiency Rating

0.82 Uniform Energy Factor (UEF)

Pros & cons42

Pros

• Supplies 7.0 GPM at a 35°F rise to support 2 to 3 simultaneous showers
• Eliminates indoor venting hardware by utilizing an outdoor wall-mount configuration
• Achieves a 0.82 Uniform Energy Factor to reduce residential gas consumption
• Durable metal cabinet includes built-in freeze protection and 1°F digital controls

Cons

• Requires outdoor mounting and professional natural gas line plumbing
• Does not include WiFi hardware for smartphone monitoring

5

LECLOC Mini Tankless Instant Water Heater Under Sink, 3kW 120V

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  9.0
• Brand
  LECLOC

Key specs2

Power Hookup

120V plug-in cord (3kW)

Intended Application

Designed strictly for single point-of-use warm water at utility or bathroom sinks, avoiding the complex hardwiring of whole-house units.

Pros & cons42

Pros

• Plug-in 120V corded design allows straightforward point-of-use installation
• Front rotary knob provides quick temperature adjustments between 30°C and 55°C
• Weighs only 3.9 pounds with a slim depth for restricted under-sink areas
• Features comprehensive safety protections including IPX4 water resistance

Cons

• Low 3kW heating capacity is restricted to single-sink handwashing and cannot run a shower
• Inlet water temperature heavily impacts maximum warmth and output flow

6

Rheem RTG-70DVLN-3 High Efficiency Non-Condensing Indoor Tankless Natural Gas Water

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  8.9
• Brand
  Rheem

Key specs2

Venting Requirements

Requires dedicated indoor direct-vent ducting to draw outside combustion air and safely exhaust flue gases outdoors.

Leak Prevention System

Integrated LeakGuard internal detection

Pros & cons42

Pros

• Supports 2 to 3 showers simultaneously with 7.0 GPM output at a 35°F rise
• Direct-vent indoor system allows safe placement inside basements or utility rooms
• LeakGuard internal leak detection shuts down operation to help prevent water damage
• Delivers 160,000 BTU/hr with digital temperature accuracy within 1°F

Cons

• Requires running dedicated direct-vent piping to an exterior wall or roof
• Professional gas line sizing is necessary to support the 160,000 BTU demand

7

Rheem RTG-70XLP-3 High Efficiency Non-Condensing Outdoor Tankless Liquid Propane Water

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  8.7
• Brand
  Rheem

Key specs2

Fuel Type Compatibility

Liquid propane (160,000 BTU/hr)

Outdoor Weatherproofing

Constructed with a heavy-duty metal enclosure and built-in freeze protection to withstand exterior residential mounting.

Pros & cons42

Pros

• Supplies 7.0 GPM continuous flow configured specifically for dedicated liquid propane
• Outdoor cabinet eliminates the need for cutting vent penetrations through living spaces
• Delivers 160,000 BTU/hr to provide hot water across 2 to 3 fixtures at once
• Features digital controls, freeze defense, and a 15-year heat exchanger warranty

Cons

• Not compatible with municipal natural gas lines without a separate burner conversion
• Restricted to outdoor exterior mounting locations

8

Rheem RRTGH84DVLN3701171 Rheem RTGH Series 8.4 GPM 157,000 BTU 120

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  8.4
• Brand
  Rheem

Key specs2

Condensing Efficiency

0.93 UEF condensing technology

Burner Heat Output

157,000 BTU/hr natural gas

Pros & cons42

Pros

• Industry-leading condensing design achieves a high 0.93 Uniform Energy Factor
• Generates 8.4 GPM at a 35°F rise to comfortably supply 3 to 4 simultaneous showers
• Direct-vent indoor configuration meets strict ultra-low NOx emissions standards
• Maintains steady output with a 157,000 BTU natural gas condensing burner

Cons

• Condensing operation produces acidic condensate that requires dedicated drainage
• Heavier 59.88-pound construction requires sturdy wall bracket reinforcement

9

Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray

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  8.1
• Brand
  Rheem

Key specs2

Electrical Service Requirement

• 240V single-phase power connection
• Three 40-amp double-pole circuit breakers
• Three runs of 8 AWG copper conductors
• Recommended 200-amp minimum electrical panel

Whole-Home Electric Flow

Up to 5.9 GPM across multiple fixtures

Pros & cons42

Pros

• Delivers up to 5.9 GPM of tankless hot water without requiring gas lines or venting
• Digital thermostatic dial adjusts temperatures in 1-degree steps from 80°F to 140°F
• Compact 3.5-inch depth mounts flush to interior drywall to free up floor space
• Provides continuous heating across multiple household fixtures simultaneously

Cons

• Requires a minimum 200-amp household electrical panel to support high power draw
• Demands three 40-amp double-pole breakers and three dedicated 8 AWG wire runs

10

Rheem 18kW 240V Tankless Electric Water Heater, Gray

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  7.9
• Brand
  Rheem

Key specs2

Heating Element Design

Dual field-serviceable copper immersion

Water Connection Size

Bottom 3/4-inch NPT connections

Pros & cons42

Pros

• Delivers up to 4.4 GPM continuous hot water using self-modulating power technology
• Dual copper immersion heating elements are durable and field serviceable
• Standard bottom 3/4-inch NPT water connections simplify plumbing hookups
• External digital thermostatic control maintains temperature accuracy to 1°F

Cons

• May not support multiple high-flow showers simultaneously in colder climates
• Requires substantial 240V electrical capacity that must be verified prior to purchase

11

Rheem RTGH Series 6.8 GPM Natural Gas Tankless Water Heater

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  7.5
• Brand
  Rheem

Key specs2

Condensing Efficiency

0.93 UEF (uses up to 34% less energy)

Energy Efficiency Rating

Extracts additional heat from flue exhaust gases to achieve a 0.93 UEF rating, lowering gas consumption compared to standard non-condensing heaters.

Pros & cons42

Pros

• Condensing heat exchanger delivers high-efficiency 0.93 UEF performance
• Produces 6.8 GPM at a 35°F rise powered by an efficient 120,000 BTU gas burner
• Indoor direct-vent system complies with ultra-low NOx clean air standards
• Protected by a 15-year heat exchanger warranty and 5-year parts coverage

Cons

• Condensate drain line installation is required alongside direct-vent ducting
• Capped at 2 to 3 showers, which may limit larger multi-bath households

12

18L Tankless Water Heater Propane with Digital Display 4.76 GPM

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  7.4
• Brand
  Baococo

Key specs2

Portable Fuel & Firing Rate

115,425 BTU/hr liquid propane

Included Shower Accessories

Comes equipped with a specialized shower head featuring a one-button flow cutoff to conserve water while camping or cleaning gear outdoors.

Pros & cons42

Pros

• Packs 115,425 BTU/hr of propane heating power into a portable outdoor design
• Delivers a maximum flow of 4.76 GPM for outdoor showers, RV hookups, and pet washing
• Includes a portable shower head featuring an integrated one-button shut-off switch
• Equipped with 6 safety protections including flame failure and antifreeze cutoff

Cons

• Requires an open-air outdoor environment and cannot be installed inside living quarters
• Maximum water temperature tops out at 113°F

Last update on 2026-10-22 / Affiliate links / Images, Product Titles, and Product Highlights from Amazon Product Advertising API

Can a continuous hot water heater run two showers at the same time?

Yes, provided the heater delivers enough flow capacity to match the combined demand of both showerheads. Whole-house natural gas and propane models provide flow rates between 7.0 GPM and 8.4 GPM at a 35-degree Fahrenheit temperature rise, which easily supports simultaneous fixtures. High-capacity electric options, such as a 24kW 240V unit, can deliver up to 5.9 GPM. If your household runs multiple fixtures at once, your total simultaneous water draw must stay within the unit's rated flow rate, or water pressure and temperature will drop.

What electrical service or fuel supply is required for a continuous water heater?

Utility requirements depend entirely on the heater's fuel source and heating power. Whole-home electric models require significant electrical service, such as a dedicated 240V connection for an 18kW or 24kW unit. Before installing, verify that your breaker box has adequate panel capacity by reviewing our guide on electric tankless water heaters to match panel capacity. Residential gas models require dedicated gas supply lines rated to support heating inputs ranging from 120,000 BTU up to 180,000 BTU, alongside a standard 120V connection for digital controls.

What is the difference between a point-of-use heater and a whole-home system?

Point-of-use heaters are designed exclusively for a single fixture with low flow requirements, whereas whole-home systems supply an entire plumbing network. Compact 110V or 120V units drawing 3000W (3kW) install directly under a sink to heat water for handwashing, and the manufacturer explicitly notes they are not suitable for showers or multiple taps at once. Whole-home heaters use 240V electric connections or high-output gas burners to produce 5.9 GPM to 8.4 GPM, supplying sufficient hot water for back-to-back showers and major household appliances.

What is the difference between outdoor and indoor direct-vent tankless heaters?

Outdoor tankless heaters vent combustion gases directly into the open air from their exterior casing, while indoor units require specialized direct-vent piping to route exhaust safely outside. High-efficiency indoor condensing units feature a 0.93 Uniform Energy Factor (UEF) and direct-vent exhaust configurations that pull fresh air while discharging flue gases. Outdoor non-condensing models carry a 0.82 UEF and eliminate the need for indoor venting pipes or wall penetrations, but they must be mounted on an exterior wall with proper clearances.

How does incoming water temperature affect continuous flow rates?

Incoming groundwater temperature determines how many gallons per minute a heater can produce at your preferred shower temperature. Flow ratings are measured against specific heating demands, such as delivering 6.8, 7.0, or 8.4 GPM at a 35-degree Fahrenheit temperature rise. When incoming ground water is colder during winter months, the heater requires more heating energy to reach the set temperature, which lowers the maximum flow rate compared to summer operation.

What options exist for continuous hot water in an RV or camper?

Campers require compact units designed specifically for mobile plumbing and low-voltage electrical systems. Dedicated RV tankless heaters run on a 12V DC connection paired with a 60,000 BTU propane burner to supply continuous hot water on demand. These specialized heaters fit standard vehicle cutouts, including 15-by-15-inch and 15-by-18-inch door openings, providing continuous hot water without demanding high-voltage 240V household power supplies.