Rheem Tankless Water Heaters: 15 Picks Ranked by Specs
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Finding the best rheem tankless water heaters depends on your fuel supply, electrical capacity, and household flow demand. Rheem offers indoor and outdoor units powered by electricity, natural gas, or propane, with capacities ranging from compact 3.5 kW single-sink models to 11.2 GPM whole-house systems.
The Rheem 18kW 240V Electric Tankless Water Heater takes the top spot because it supplies up to 4.4 GPM for moderate-demand homes with 240V electric service without requiring venting. This guide compares 15 models based strictly on the specifications published on their listings to help you match your setup.
Quick picks
Our 15 picks
Rheem 18kW 240V Electric Tankless Water Heater
Best for: moderate-demand homes with 240V electric service
- Fuel Type
- Electric
- Flow Rate
- 4.4 GPM
- Wattage
- 18 kW
- Voltage
- 240 V
- Temperature Control
- ±1°F
- Dimensions
- 3.5 x 14.5 x 18.5 inches
View on Amazon: Rheem 18kW 240V Electric Tankless Water Heater
This whole-house electric tankless water heater delivers up to 4.4 GPM using an 18 kW, 240V electrical configuration. It features self-modulating copper immersion elements and an external digital display accurate to 1°F. If you need a compact electric unit for moderate household water demands without installing gas lines or venting, this model fits standard 3/4-inch NPT plumbing and mounts directly on your wall.
Pros
- Up to 4.4 GPM flow rate
- Digital temperature control accurate to 1°F
- Two field-serviceable copper immersion heating elements
- Standard 3/4-inch bottom NPT water connections
Cons
- Requires a 240V dedicated electrical setup
- Maximum flow rate limited to 4.4 GPM
Good fit if
- You have a dedicated 240V electrical supply available.
- You need up to 4.4 GPM of hot water for whole-house use.
- You want external digital temperature controls with 1°F precision.
Skip if
- You need flow rates higher than 4.4 GPM for high-demand households.
- You only have a standard 120V electrical line available.
Verdict: Rheem 18kW 240V Electric Tankless Water Heater provides reliable whole-house hot water up to 4.4 GPM with precise digital temperature control. It offers efficient electric heating in a compact wall-mounted design without requiring venting.
Rheem 13kW Compact Electric Tankless Water Heater
Best for: single-fixture setups and low-flow bathrooms
- Voltage
- 240V
- Dimensions
- 12.6 × 8.25 × 3.63 inches
- Weight
- 3.97 pounds
View on Amazon: Rheem 13kW Compact Electric Tankless Water Heater
This Rheem electric unit delivers on-demand hot water using a 13kW, 240V heating system requiring 54 amps. It provides a maximum flow rate of 3.17 GPM, modulated across two copper immersion heating elements. With 99.8% efficiency and precise digital temperature control in single-degree increments, it suits you if you need compact point-of-use heating or supply for a single low-flow bathroom.
Pros
- Digital LED thermostatic control with 1-degree accuracy
- 99.8% energy efficiency rating
- Up to 3.17 GPM flow rate
- Dual field-serviceable copper immersion heating elements
Cons
- Draws 54 amps, requiring adequate 240V electrical capacity
- Maximum flow rate limited to 3.17 GPM
Good fit if
- You need hot water for a single shower or sink fixture.
- You have a 240V electrical connection that supports a 54A draw.
- You want compact dimensions for tight installation spaces.
Skip if
- You require simultaneous hot water across multiple high-demand fixtures.
- You only have a 120V electrical service available.
Verdict: Rheem 13kW 240V Tankless Electric Water Heater gives you compact, 99.8% efficient heating for low-demand applications without taking up floor space. It delivers up to 3.17 GPM, making it a practical fit for dedicated point-of-use setups or small living spaces.
Rheem RTG 9.5 GPM Natural Gas Water Heater
Best for: large homes running multiple fixtures simultaneously
- Fuel Type
- Natural Gas
- Flow Rate
- 9.5 GPM
- BTU
- 199,900 BTU/hr
- Installation Location
- Indoor
- Temperature Control
- ±1°F
- Certification
- CSA
This indoor natural gas tankless water heater delivers up to 9.5 GPM at a 35°F temperature rise, powered by a 199,900 BTU burner. With an 0.82 Uniform Energy Factor and non-condensing direct venting, it supplies enough capacity to run three to four showers at once. Built-in WiFi lets you monitor operation, while precision controls allow adjustments down to 1°F. It suits multi-bathroom households needing high-demand indoor heating.
Pros
- Delivers 9.5 GPM flow rate using a 199,900 BTU natural gas burner
- Supports 3 to 4 simultaneous showers at a 35°F temperature rise
- Features WiFi monitoring and ±1°F digital temperature adjustments
- Backed by a 15-year heat exchanger and 5-year parts warranty
Cons
- 0.82 UEF rating is lower than condensing models
- Requires direct vent piping for indoor installation
Good fit if
- You have a natural gas supply and need to run 3 to 4 fixtures simultaneously.
- You want built-in WiFi connectivity and precise 1°F temperature increments.
Skip if
- You need a liquid propane or outdoor-rated water heater.
- You prefer a condensing model with a higher energy factor.
Verdict: Rheem RTG 9.5 GPM Indoor Natural Gas Water Heater offers substantial heating capacity for multi-bathroom homes that require high simultaneous flow. Its non-condensing design and integrated WiFi provide dependable indoor output without sacrificing precise temperature control.
Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater
Best for: Large homes with outdoor natural gas hookups
- Fuel Type
- Natural Gas
- Flow Rate
- 9.5 GPM
- BTU
- 199,900 BTU/hr
- Installation Location
- Outdoor
- Temperature Control
- ±1°F
- Certification
- CSA
View on Amazon: Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater
This is an outdoor natural gas tankless water heater designed for whole-house use. It delivers up to 9.5 GPM at a 35°F temperature rise with a 199,900 BTU per hour maximum burner rate and a 0.82 UEF rating. Because you mount it outdoors, you avoid running dedicated indoor venting. It suits large homes needing simultaneous hot water across three to four fixtures.
Pros
- Delivers 9.5 GPM flow rate at a 35°F temperature rise
- Generates up to 199,900 BTU/hr for high-demand households
- Outdoor wall mounting eliminates indoor exhaust venting requirements
- Digital LED control panel provides precision temperature adjustments within ±1°F
Cons
- Requires outdoor exterior wall mounting
- Non-condensing 0.82 UEF rating is lower than condensing options
- Base configuration does not include Wi-Fi functionality
Good fit if
- You have an exterior mounting location with a natural gas supply.
- You need to supply hot water for three to four simultaneous showers.
- You want to avoid installing indoor exhaust venting pipes.
Skip if
- You require an indoor water heater or use liquid propane.
- You want a higher-efficiency condensing unit.
- You prefer built-in Wi-Fi connectivity without selecting that specific variation.
Verdict: Rheem RTG 9.5 GPM Outdoor Natural Gas Heater delivers 199,900 BTU/hr of high-capacity water heating without requiring indoor venting. It provides dependable whole-home flow for large households with exterior installation access.
Rheem RTG 9.5 GPM Outdoor Propane Tankless Heater
Best for: outdoor installation in multi-bathroom propane-powered homes
- Fuel Type
- Liquid Propane
- Flow Rate
- 9.5 GPM at 35°F rise
- BTU
- 199,900 BTU/hr
- Installation Location
- Outdoor
- Temperature Control
- Digital LED, ±1°F
- Certification
- CSA
View on Amazon: Rheem RTG 9.5 GPM Outdoor Propane Tankless Heater
This whole-house tankless water heater runs on liquid propane and installs outdoors, which removes the need for indoor venting. It delivers up to 9.5 GPM at a 35°F temperature rise with a maximum heat output of 199,900 BTU/hr. If you have multiple bathrooms and a dedicated propane supply, this unit provides enough capacity to run three to four showers at once while maintaining temperature accuracy within 1°F.
Pros
- High flow capacity of 9.5 GPM at a 35°F temperature rise
- 199,900 BTU/hr heat input for multi-bathroom demand
- Outdoor wall-mount design requires no indoor exhaust venting
- 15-year heat exchanger and 5-year parts warranty coverage
Cons
- Requires liquid propane supply; incompatible with natural gas lines
- Outdoor-only mounting limits installation to exterior walls
- Non-condensing 0.82 UEF rating is lower than condensing units
Good fit if
- You heat water using a dedicated liquid propane supply.
- You prefer an exterior wall installation to avoid indoor venting runs.
- You need high flow rates to support up to four simultaneous showers.
Skip if
- You need an indoor water heater or use natural gas.
- You live in an area requiring an ultra-high efficiency condensing unit.
Verdict: Rheem RTG 9.5 GPM Outdoor Liquid Propane Water Heater delivers high flow rates for propane homes without the hassle of indoor vent pipes. It is a capable whole-house option if you have exterior mounting space.
Rheem RTG Series 7.0 GPM Propane Tankless Water Heater
Best for: Propane homes running two to three showers
- Fuel Type
- Liquid Propane
- Flow Rate
- 7.0 GPM
- BTU
- 160,000 BTU/hr
- Installation Location
- Indoor
- Temperature Control
- ±1°F
- Certification
- CSA
View on Amazon: Rheem RTG Series 7.0 GPM Propane Tankless Water Heater
This indoor liquid propane tankless water heater delivers up to 7.0 GPM with a 160,000 BTU burner. Its non-condensing design features a 0.82 Uniform Energy Factor and requires direct venting indoors. With digital temperature adjustments within 1°F, it supports two to three simultaneous showers. This unit suits you if you heat with propane and need reliable whole-house hot water delivery without taking up floor space.
Pros
- Delivers up to 7.0 GPM output rated at 160,000 BTU/hr
- Digital LED panel allows temperature adjustments within ±1°F
- Wall-mount unit measuring 24.2 by 13.5 by 10.3 inches
- Includes 15-year heat exchanger and 5-year parts warranty coverage
Cons
- Lacks built-in WiFi connectivity
- Lower 0.82 UEF efficiency than condensing alternatives
- Requires direct indoor venting and professional installation
Good fit if
- You run a dedicated liquid propane supply.
- You need sufficient flow for two to three simultaneous showers.
- You want an indoor wall-mounted installation.
Skip if
- You use natural gas instead of propane.
- You require built-in WiFi functionality.
- You prefer an outdoor unit to avoid indoor venting requirements.
Verdict: Rheem RTG 7.0 GPM Indoor Propane Water Heater offers steady multi-bath flow and precise digital controls for propane-fueled homes. It delivers dependable indoor heating backed by a 15-year heat exchanger warranty.
Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater
Best for: indoor natural gas setups with multiple showers
- Fuel Type
- Natural Gas
- Flow Rate
- 6.8 GPM
- BTU
- 120,000 BTU/hr
- Installation Location
- Indoor
- Temperature Control
- ±1°F
- Certification
- CSA
View on Amazon: Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater
The Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater provides on-demand hot water using a condensing design with a 0.93 Uniform Energy Factor. It delivers up to 6.8 GPM at a 35°F rise from 120,000 BTU/hr of natural gas. Built for direct-vent indoor installation, this unit suits you if you run two to three simultaneous showers and want precise temperature adjustments down to 1°F.
Pros
- 0.93 Uniform Energy Factor condensing efficiency
- Flow rate of 6.8 GPM at a 35°F rise
- Digital LED control with ±1°F temperature precision
- 15-year heat exchanger and 5-year parts warranty
Cons
- No Wi-Fi connectivity included on this model size
- Requires direct venting for indoor installation
Good fit if
- You have an indoor natural gas supply with direct vent capability.
- You need sufficient flow for two to three simultaneous showers.
- You want high energy efficiency supported by a 0.93 UEF rating.
Skip if
- You need a liquid propane or outdoor-mounted water heater.
- You require factory-installed Wi-Fi control.
- You need higher peak flow than 6.8 GPM or more than 120,000 BTU/hr.
Verdict: Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater delivers efficient condensing performance for homes running up to three showers at once. Its 0.93 UEF rating and 120,000 BTU/hr natural gas burner offer reliable indoor heating without taking up floor space.
Rheem RTGH 9.5 GPM Propane Tankless Water Heater
Best for: Large homes running on liquid propane
- Fuel Type
- Liquid Propane
- Flow Rate
- 9.5 GPM
- BTU
- 199,900 BTU/hr
- Installation Location
- Indoor
- Temperature Control
- ±1°F
- Certification
- CSA
View on Amazon: Rheem RTGH 9.5 GPM Propane Tankless Water Heater
The Rheem RTGH 9.5 GPM Indoor Propane Tankless Water Heater delivers up to 9.5 GPM using liquid propane and a 199,900 BTU burner. Its condensing design reaches a 0.93 Uniform Energy Factor to maximize efficiency during indoor direct-vent operation. You get digital temperature control accurate to 1°F and capacity for three to four simultaneous showers. It suits large homes that rely on propane storage rather than a municipal natural gas connection.
Pros
- High 9.5 GPM maximum flow rate powered by 199,900 BTU/hr
- Condensing operation achieves a 0.93 Uniform Energy Factor
- Digital LED control with precision within 1°F
- Includes built-in freeze protection
Cons
- Requires a liquid propane supply instead of natural gas
- Does not include built-in Wi-Fi connectivity
- Requires indoor direct-vent piping through an exterior wall or roof
Good fit if
- You heat with liquid propane and need whole-house capacity.
- You run up to four showers simultaneously and require high flow.
- You want a high-efficiency 0.93 UEF condensing unit installed indoors.
Skip if
- You use municipal natural gas rather than liquid propane.
- You prefer an outdoor installation to avoid dedicated venting.
- You require built-in Wi-Fi monitoring right out of the box.
Verdict: Rheem RTGH 9.5 GPM Indoor Propane Tankless Water Heater provides high flow rates and 0.93 UEF efficiency for propane-powered homes with multiple bathrooms. Its indoor direct-vent configuration and freeze protection deliver dependable, high-capacity hot water.
Rheem IKONIC 11.2 GPM Propane Tankless Water Heater
Best for: high-demand propane homes needing built-in recirculation
- Fuel Type
- Liquid Propane
- Flow Rate
- 11.2 GPM
- BTU
- 199,900 BTU/hr
- Installation Location
- Indoor
- Dimensions
- 28.6 x 17.3 x 13.7 inches
- Features
- WiFi
View on Amazon: Rheem IKONIC 11.2 GPM Propane Tankless Water Heater
This indoor condensing tankless water heater runs on liquid propane and provides up to 11.2 GPM with an input of 199,900 BTU/hr. It includes built-in recirculation and integrated Wi-Fi for monitoring usage and adjusting temperatures from a mobile device. With a 1/2-inch side clearance requirement and a quick hang bracket, it suits large homes that need high simultaneous hot water delivery across multiple bathrooms and appliances.
Pros
- High flow rate up to 11.2 GPM with 199,900 BTU/hr heating capacity
- Integrated recirculation system eliminates delays for hot water delivery
- Built-in EcoNet Wi-Fi enables remote scheduling and usage tracking
- Compact installation profile requiring 1/2-inch side clearance
Cons
- Requires an additional kit if mounted outdoors
- Weighs 86 pounds, requiring reinforced wall mounting
- Runs exclusively on liquid propane rather than natural gas
Good fit if
- You use liquid propane and require high flow for simultaneous fixtures.
- You want built-in recirculation without installing an external pump.
- You prefer monitoring water and energy usage through a mobile application.
Skip if
- You have a natural gas connection or an all-electric utility setup.
- You need an outdoor-ready unit without purchasing a conversion kit.
Verdict: Rheem IKONIC 11.2 GPM Propane Tankless Water Heater provides high-volume indoor hot water delivery backed by built-in recirculation and Wi-Fi monitoring. It is a strong match for propane-supplied homes running multiple showers and appliances simultaneously.
Rheem 2.5 Gallon Mini-Tank Electric Water Heater
Best for: point-of-use single sink hot water supply
- Fuel Type
- Electric
- Capacity
- 2.5 gallons
- Temperature Control
- 50°F-140°F
- Dimensions
- 11"W x 17"H x 11"L
- Weight
- 17.6 pounds
View on Amazon: Rheem 2.5 Gallon Mini-Tank Electric Water Heater
This point-of-use electric water heater stores 2.5 gallons of water in an enameled glass-lined tank. It measures 11 inches wide, 11 inches long, and 17 inches high, weighing 17.6 pounds. You can adjust the water temperature from 50°F to 140°F. The unit mounts on the floor or the wall with the included bracket. It suits you if you need localized hot water directly at a single sink.
Pros
- Adjustable temperature control from 50°F to 140°F
- Floor and wall mountable with included bracket
- Enameled glass-lined tank for extended life
- Compact 11-inch by 11-inch base footprint
Cons
- Capacity limited to 2.5 gallons rather than continuous flow
- Weighs 17.6 pounds before filling with water
Good fit if
- You need dedicated hot water for a single point of use.
- You want flexible installation with floor or wall mounting options.
- You require water temperatures adjustable between 50°F and 140°F.
Skip if
- You need continuous on-demand hot water for whole-home fixtures.
- You lack clearance for an 11 by 17 by 11-inch cabinet installation.
Verdict: Rheem 2.5 Gallon Mini-Tank Electric Water Heater provides dedicated point-of-use heating with flexible floor or wall mounting. Its 2.5-gallon glass-lined tank and 50°F to 140°F range make it practical for individual fixtures.
Rheem Prestige 11 GPM Condensing Water Heater
Best for: high-demand indoor natural gas setups
- Fuel Type
- Natural Gas
- Flow Rate
- 11.0 GPM
- Installation Location
- Indoor
- Dimensions
- 28.7 x 17.3 x 14.8 inches
- Venting Type
- Condensing
View on Amazon: Rheem Prestige 11 GPM Condensing Water Heater
This indoor condensing tankless water heater runs on natural gas and delivers up to 11.0 GPM. It features built-in recirculation, automated usage tracking via Auto-Learn programming, and integrated water and gas leak detection that shuts down the unit during a fault. Measuring 28.7 by 17.3 by 14.8 inches, it suits indoor setups where you need high flow rates and automated demand management from an existing natural gas supply.
Pros
- Maximum flow rate of 11.0 GPM
- Built-in recirculation system
- Auto-Learn programming tracks usage patterns
- Water and gas leak detection with automated shutdown
Cons
- Configured only for natural gas, not liquid propane
- Designed solely for indoor installation
Good fit if
- You have a natural gas supply line indoors.
- You need high simultaneous demand up to 11.0 GPM.
- You want built-in recirculation with auto-learning schedule tracking.
Skip if
- You need an outdoor-rated water heater.
- You rely on propane or electric utilities.
Verdict: Rheem 11.0 GPM Condensing Natural Gas Heater delivers high flow output and built-in recirculation for indoor natural gas setups. Automated leak shutoff and usage tracking provide reliable protection and scheduling.
Rheem 240V 3-Chamber Electric Tankless Water Heater
Best for: Homes needing multi-chamber 240V electric water heating
- Voltage
- 240V
- Dimensions
- 1 × 1 × 1 inches
- Weight
- 17.8 pounds
View on Amazon: Rheem 240V 3-Chamber Electric Tankless Water Heater
This Rheem 240V electric tankless water heater provides residential hot water using three copper immersion heating elements. The unit features self-modulating power management that adapts directly to your hot water demand, alongside an external digital display offering temperature adjustments within 1 degree. It connects through standard bottom 3/4-inch NPT fittings and weighs 17.8 pounds. It suits your home if you want direct electric heating with field-serviceable components.
Pros
- External digital control with 1-degree temperature accuracy
- Three field-serviceable copper immersion heating elements
- Bottom 3/4-inch NPT water connections for standard installation
- Self-modulating design adjusts power to demand
Cons
- No flow rate GPM listed in published specifications
- Requires a 240V high-voltage electrical setup
Good fit if
- You need a 240V electric system with standard 3/4-inch NPT bottom water connections.
- You want precise temperature adjustments via a digital LED thermostat.
- You prefer field-serviceable copper immersion heating elements.
Skip if
- You require a gas or liquid propane water heater.
- You lack electrical panel capacity for a 240V tankless appliance.
Verdict: Rheem 240V 3-Chamber Electric Tankless Water Heater delivers steady electric heating with precise one-degree controls and three field-serviceable copper chambers. It is a solid pick if your home supports a dedicated 240V electric setup.
Rheem 3.5kW 120V Point-of-Use Electric Heater
Best for: single-sink point-of-use 120V electrical setups
- Fuel Type
- Electric
- Voltage
- 120V
- Dimensions
- 10.9 × 5.88 × 2.75 inches
- Weight
- 4.5 pounds
View on Amazon: Rheem 3.5kW 120V Point-of-Use Electric Heater
This compact electric unit provides point-of-use heating using a standard 120V electrical connection and a 3.5kW heating element. Measuring 10.9 inches long by 5.88 inches wide and weighing 4.5 pounds, it fits inside tight spaces near your sink. You get a digital display showing output temperature from 80°F to 140°F. It suits you if you need a single-fixture electric option without upgrading to a 240V circuit.
Pros
- Operates on standard 120V electrical service
- Weighs 4.5 pounds with compact 10.9 by 5.88-inch footprint
- Digital display shows output temperatures from 80°F to 140°F
- 3.5kW power draw suits point-of-use electrical installations
Cons
- Non-thermostatically controlled operation
- Limited 3.5kW output restricted to single point-of-use applications
Good fit if
- You need a dedicated point-of-use heater operating on 120V power.
- You have limited space and require an under-cabinet unit under 11 inches long.
- You only need warm water for a single low-demand fixture.
Skip if
- You require precise thermostatic temperature control.
- You need a whole-house or multi-fixture 240V water heater.
- You want a gas or liquid propane unit.
Verdict: Rheem 3.5kW 120V Point-of-Use Electric Heater delivers dedicated single-sink heating on a standard 120V line without requiring 240V electrical panel upgrades. Its non-thermostatic design and 3.5kW draw keep it focused strictly on low-demand, point-of-use applications.
Rheem 36 kW 6 GPM Electric Tankless Water Heater
Best for: all-electric homes requiring high flow capacity
- Fuel Type
- Electric
- Flow Rate
- 6 GPM
- Wattage
- 36 kW
- Dimensions
- 18.3 x 21.6 x 21.6 inches
- Weight
- 19 pounds
View on Amazon: Rheem 36 kW 6 GPM Electric Tankless Water Heater
This Rheem electric tankless water heater supplies hot water using a 36 kW heating system. It delivers a flow rate of up to 6 GPM, operating entirely on electricity without venting requirements. At 19 pounds and measuring 18.3 by 21.6 by 21.6 inches, it mounts directly to wall spaces. You will find it suits high-demand households equipped with sufficient electrical service.
Pros
- High 36 kW power rating
- Flow rate up to 6 GPM
- Self-modulating power output
- Lightweight 19-pound design
Cons
- Refurbished unit condition
- Requires substantial 36 kW electrical capacity
- May ship in generic packaging
Good fit if
- You need up to 6 GPM of electric hot water output.
- You have an electrical setup capable of supplying 36 kW.
- You want a lightweight 19-pound wall-mounted unit.
Skip if
- You require a brand-new unit rather than a refurbished model.
- You prefer gas or liquid propane fuel sources.
- Your electrical service cannot support 36 kW demand.
Verdict: Rheem 36 kW 6 GPM Electric Tankless Water Heater delivers high flow rates for homes with adequate electrical service.
Rheem 36 kW Electric Tankless Water Heater
Best for: high-demand 240-volt electric whole-home heating
- Fuel Type
- Electric
- Wattage
- 36kW
- Voltage
- 240V
- Temperature Control
- Ext Adj Temp Ctrl
- Dimensions
- Bot 3/4 in. Npt Con
- Weight
- 24.4 pounds
This unit is a high-output electric tankless water heater designed for 240-volt electrical systems. It provides 36 kW of heating power and features an external adjustable temperature control for direct heat management. With bottom 3/4-inch NPT plumbing connections and a 24.4-pound silver casing, it gives you high electric heating capacity without gas infrastructure. It suits you if your home supports high-draw 240-volt circuits.
Pros
- 36 kW power rating for high electric heating output
- External adjustable temperature control
- Bottom 3/4-inch NPT water connections
- 24.4-pound compact silver housing
Cons
- Requires a high-capacity 240-volt electrical setup
- Electric power source with no gas or propane option
Good fit if
- You need a 36 kW electric heater running on a 240-volt service.
- You want an external adjustable temperature control interface.
- You prefer bottom-mounted 3/4-inch NPT plumbing connections.
Skip if
- You require a natural gas or liquid propane water heater.
- You do not have the electrical capacity for a 36 kW, 240V appliance.
Verdict: Rheem 36kW 240V Electric Tankless Water Heater delivers 36 kW of electric heating with convenient external adjustable controls and standard 3/4-inch NPT connections. It is a capable choice if your electrical service supports high 240V loads.
Specifications side by side
| Spec | Rheem 18kW 240V Electric Tankless Water Heater | Rheem 13kW Compact Electric Tankless Water Heater | Rheem RTG 9.5 GPM Natural Gas Water Heater | Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater | Rheem RTG 9.5 GPM Outdoor Propane Tankless Heater | Rheem RTG Series 7.0 GPM Propane Tankless Water Heater | Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater | Rheem RTGH 9.5 GPM Propane Tankless Water Heater | Rheem IKONIC 11.2 GPM Propane Tankless Water Heater | Rheem 2.5 Gallon Mini-Tank Electric Water Heater | Rheem Prestige 11 GPM Condensing Water Heater | Rheem 240V 3-Chamber Electric Tankless Water Heater | Rheem 3.5kW 120V Point-of-Use Electric Heater | Rheem 36 kW 6 GPM Electric Tankless Water Heater | Rheem 36 kW Electric Tankless Water Heater |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Fuel Type | Electric | not specified | Natural Gas | Natural Gas | Liquid Propane | Liquid Propane | Natural Gas | Liquid Propane | Liquid Propane | Electric | Natural Gas | not specified | not specified | Electric | Electric |
| Flow Rate | 4.4 GPM | not specified | 9.5 GPM | 9.5 GPM | 9.5 GPM at 35°F rise | 7.0 GPM | 6.8 GPM | 9.5 GPM | 11.2 GPM | not specified | 11.0 GPM | not specified | not specified | 6 GPM | not specified |
| BTU | not specified | not specified | 199,900 BTU/hr | 199,900 BTU/hr | 199,900 BTU/hr | 160,000 BTU/hr | 120,000 BTU/hr | 199,900 BTU/hr | 199,900 BTU/hr | not specified | not specified | not specified | not specified | not specified | not specified |
| Wattage | 18 kW | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | 36 kW | 36kW |
| Installation Location | not specified | not specified | Indoor | Outdoor | Outdoor | Indoor | Indoor | Indoor | Indoor | not specified | Indoor | not specified | not specified | not specified | not specified |
| Capacity | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | 2.5 gallons | not specified | not specified | not specified | not specified | not specified |
| Voltage | 240 V | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | 240V |
| Temperature Control | ±1°F | not specified | ±1°F | ±1°F | Digital LED, ±1°F | ±1°F | ±1°F | ±1°F | not specified | 50°F-140°F | not specified | not specified | not specified | not specified | Ext Adj Temp Ctrl |
| Certification | not specified | not specified | CSA | CSA | CSA | CSA | CSA | CSA | not specified | not specified | not specified | not specified | not specified | not specified | not specified |
| Dimensions | 3.5 x 14.5 x 18.5 inches | not specified | 24.2 x 13.5 x 10.3 inches | 20.8 x 13.5 x 9.4 inches | 20.8 x 13.5 x 9.4 inches | 24.2 x 13.5 x 10.3 inches | 23.7 x 17.7 x 9.8 inches | 23.7 x 17.7 x 9.8 inches | 28.6 x 17.3 x 13.7 inches | 11"W x 17"H x 11"L | 28.7 x 17.3 x 14.8 inches | not specified | not specified | 18.3 x 21.6 x 21.6 inches | Bot 3/4 in. Npt Con |
| Use | Whole House | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified | not specified |
| Venting Type | not specified | not specified | Non-Condensing | Non-Condensing | Non-Condensing | Non-Condensing | not specified | not specified | not specified | not specified | Condensing | not specified | not specified | not specified | not specified |
| Features | not specified | not specified | WiFi | WiFi | WiFi | WiFi | WiFi | WiFi | WiFi | not specified | not specified | not specified | not specified | not specified | not specified |
| Weight | 14.8 pounds | 3.97 pounds | 46.5 pounds | 39.3 pounds | 39.3 pounds | 46.5 pounds | 59.9 pounds | 59.9 pounds | 86 pounds | 17.6 pounds | not specified | 17.8 pounds | 4.5 pounds | 19 pounds | 24.4 pounds |
| Size | Small | Compact | 9.5 GPM (WiFi) | 9.5 GPM (No WiFi) | 9.5 GPM (Non-WiFi) | 7.0 GPM (No WiFi) | 6.8 GPM (No WiFi) | 9.5 GPM (Without WiFi) | 11.2 GPM (w Recirc) | 2.5 Gallon | 11 GPM | not specified | not specified | not specified | not specified |
| Color | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Silver |
| Model | RTEX-18 | RTEX-13 | RTG-95DVELN-3 | RTG-95XLN-3 | RTG-95XLP-3 | RTG-70DVLP-3 | RTGH-68DVLN-3 | RTGH-95DVLP-3 | RECTGH-SR11iP | PROE2 1 RH MT | RTGH-RH11DVLN | RTEX-27 | RTEX-04 | RTEX-36 | RTEX-36 |
The Rheem Tankless Lineup at a Glance
Rheem electric units separate into point-of-use and whole-house categories. Compact 120V models like the Rheem 3.5kW 120V Point-of-Use Electric Heater power isolated sinks without panel modifications. High-voltage 240V models, such as the Rheem 18kW 240V Electric Tankless Water Heater, handle moderate demands without requiring flue vents, provided you have adequate electrical service.
Gas models serve homes with heavier flow requirements across natural gas and propane hookups. You can select outdoor units to skip exhaust piping, or indoor models with dedicated vents. Non-condensing models like the Rheem RTG 9.5 GPM Natural Gas Water Heater suit standard venting setups, while condensing options like the Rheem Prestige 11 GPM Condensing Water Heater provide maximum output for multiple simultaneous fixtures.
Where the Rheem Range Fits Best
Rheem suits you if you need compact point-of-use heaters or high-output whole-house systems. The lineup ranges from a 4.5-pound, 3.5 kW electric unit and a 2.5-gallon mini-tank up to an 86-pound propane heater delivering 11.2 GPM. Electric models scale from 3.17 GPM to 6 GPM, while gas and propane units span 6.8 GPM to 11.2 GPM.
You should note clear gaps in this selection. Exterior installation is limited strictly to natural gas and propane heaters, leaving you with no outdoor electric options. You also cannot find point-of-use gas units, as all gas models start at 6.8 GPM for multi-fixture use.
If you also need room warmth, technical specifications for the best baseboard space heaters list electrical requirements and output.
How to Choose the Right Rheem Unit
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Match Fuel to Your Home
Your available energy source dictates which Rheem model fits your home. If you have natural gas, models like the RTG 9.5 GPM provide high output. Propane users can choose the outdoor RTG 9.5 GPM or the indoor RTG 7.0 GPM. Electric homes must verify their panel capacity for 240V units like the RTEX-18. Always confirm your fuel type before comparing specs, as switching sources requires new infrastructure and permits.
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Select Proper Installation Location
Decide if the unit belongs indoors or outdoors. Outdoor models, such as the RTG 9.5 GPM Outdoor Natural Gas Heater, eliminate the need for complex indoor venting. Indoor units, like the RTG 9.5 GPM Indoor Natural Gas Water Heater, require proper ventilation and clearance. Check your space constraints and local codes. Some models offer WiFi for remote monitoring, which works best when the unit is accessible for maintenance checks.
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Determine Whole House Needs
Assess how many fixtures you run simultaneously. Whole-house units like the Rheem 18kW 240V Electric Tankless Water Heater serve multiple bathrooms. For single sinks, use point-of-use options like the RTEX-04 or the PROE2 1 RH MT mini-tank. The IKONIC 11.2 GPM Propane model handles high demand for large families. Match your peak usage to the unit’s capacity to avoid temperature drops during heavy use.
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Check Electrical Voltage Requirements
Electric models require specific voltage levels. The RTEX-04 runs on standard 120V, making it easy to install near a sink. Whole-house electric units, such as the RTEX-18, need a dedicated 240V circuit. Higher wattage models like the RTEX-36 demand significant electrical service upgrades. Verify your panel capacity before purchasing. Incorrect voltage selection leads to poor performance or tripped breakers. Always consult an electrician for high-draw installations.
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Evaluate Venting Specifications
Gas units require specific venting types. Non-condensing models, like the RTG 9.5 GPM Outdoor Natural Gas Heater, use standard exhaust pipes. Condensing units, such as the RTGH-68DVLN-3, offer higher efficiency but need specialized venting for acidic exhaust. Indoor gas heaters often use direct-vent systems. Ensure your installation site supports the required venting configuration. Proper venting is critical for safety and efficient operation of any gas-fired Rheem tankless heater.
Frequently asked questions
Which Rheem tankless water heater is best for whole-house use?
The Rheem 18kW 240V Electric Tankless Water Heater is the top pick for moderate-demand homes with 240V electric service. It provides reliable whole-house hot water up to 4.4 GPM. The unit features precise digital temperature control and a compact wall-mounted design that does not require venting.
What is the smallest Rheem electric tankless heater?
The Rheem 3.5kW 120V Point-of-Use Electric Heater is the most compact option for single-sink setups. It operates on a standard 120V line without needing panel upgrades. Weighing just 4.5 pounds, it measures 5.88 inches wide and 10.9 inches long, making it ideal for low-demand applications.
Does Rheem offer outdoor tankless water heaters?
Yes, Rheem provides outdoor models like the RTG 9.5 GPM Natural Gas and Propane heaters. These units are designed for exterior installation, eliminating the need for indoor venting. They deliver high-capacity flow for large homes and feature non-condensing designs for dependable outdoor performance.
Which Rheem model has the highest flow rate?
The Rheem IKONIC 11.2 GPM Propane Tankless Water Heater offers the highest flow rate in this lineup. It is designed for high-demand propane homes needing built-in recirculation. The unit supports multiple showers and appliances simultaneously, making it suitable for large households with significant hot water needs.
Are Rheem tankless heaters WiFi enabled?
Many Rheem models include integrated WiFi for remote monitoring. The RTG 9.5 GPM Indoor Natural Gas and IKONIC 11.2 GPM Propane units feature this capability. WiFi allows you to track usage and adjust settings remotely, adding convenience to your whole-house or point-of-use heating system.
What is the best Rheem heater for a single bathroom?
The Rheem 13kW Compact Electric Tankless Water Heater is best for single-fixture setups and low-flow bathrooms. It delivers up to 3.17 GPM with 99.8% efficiency. Its compact size and wall-mounted design make it a practical fit for dedicated point-of-use applications without taking up floor space.
Which Rheem unit is best for condensing efficiency?
The Rheem Prestige 11 GPM Condensing Water Heater is the top choice for high-efficiency indoor natural gas setups. It delivers high flow output with built-in recirculation. The condensing design maximizes energy use, while automated leak shutoff provides reliable protection for your home.