Best Rheem Natural Gas Tankless Water Heaters: 8 Spec-Based Picks
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Choosing the best rheem natural gas tankless water heaters requires matching flow rates and venting types to your home’s layout. We compared 8 models using only the specifications published on the listings. The Rheem RTG 9.5 GPM Natural Gas Water Heater leads this list because its 199,900 BTU/hr output supports multiple simultaneous showers in large indoor homes. You need to decide whether indoor or outdoor installation fits your space. This guide helps you pick the right unit for your specific hot water demands.
Quick picks
The best fit for you
- You need high flow for multiple simultaneous showers indoors Rheem RTG 9.5 GPM Natural Gas Water Heater Its 9.5 GPM flow rate and 199,900 BTU/hr output support multi-bathroom homes.
- You want vent-free outdoor installation without interior space Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater This outdoor model delivers 9.5 GPM without requiring venting pipes or indoor utility space.
- You need high condensing efficiency for moderate demand Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater Its 0.93 UEF condensing efficiency provides up to 6.8 GPM for two to three showers.
- You want built-in recirculation for high indoor demand Rheem Prestige 11 GPM Condensing Water Heater This unit offers 11 GPM capacity with integrated scheduling and leak protection features.
- You need outdoor heating with sub-zero freeze protection Rheem 6.8 GPM Outdoor Condensing Water Heater It provides 6.8 GPM with leak shutoff sensors and freeze protection for cold climates.
Our 8 picks
Rheem RTG 9.5 GPM Natural Gas Water Heater
Best for: Large indoor homes running multiple simultaneous showers
- Fuel Type
- Natural Gas (what this guide is about)
- Flow Rate
- 9.5 GPM
- BTU
- 199,900 BTU/hr
- Installation Location
- Indoor
- Temperature Control
- ±1°F
- Certification
- CSA
View on Amazon: Rheem RTG 9.5 GPM Natural Gas Water Heater Affiliate link
This indoor natural gas tankless water heater delivers up to 9.5 GPM at a 35°F rise and produces 199,900 BTU/hr. It features a non-condensing direct vent system and carries a 0.82 Uniform Energy Factor. Built-in WiFi allows connectivity, while the digital LED interface provides temperature adjustments within 1°F. It suits your home if you need to run three to four showers simultaneously.
Pros
- 9.5 GPM maximum flow rate at 35°F rise with 199,900 BTU/hr heat output
- Built-in WiFi connectivity and digital LED temperature control with ±1°F precision
- 15-year heat exchanger warranty and 5-year parts warranty
- Built-in freeze protection and flame failure safety features
Cons
- Non-condensing operation rated at 0.82 Uniform Energy Factor
- Requires indoor direct vent routing and professional installation
Good fit if
- You need sufficient capacity to run three to four showers at the same time.
- You want an indoor natural gas heater with built-in WiFi monitoring.
Skip if
- You plan to mount your water heater outdoors.
- You want a condensing heater with higher efficiency than 0.82 UEF.
Verdict: Rheem RTG 9.5 GPM Indoor Gas Tankless Heater provides 199,900 BTU/hr to supply multi-bathroom homes from an indoor location. Its non-condensing design delivers high flow rates alongside WiFi monitoring and a 15-year heat exchanger warranty.
Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater
Best for: large households needing vent-free outdoor installation
- Fuel Type
- Natural Gas (what this guide is about)
- 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 Affiliate link
The Rheem RTG 9.5 GPM Outdoor Natural Gas Water Heater is a high-output, non-condensing unit built for exterior wall mounting. It delivers up to 9.5 GPM at a 35°F temperature rise using 199,900 BTU/hr, enough to supply three to four showers at once. Because you install it outdoors, you do not need dedicated indoor venting. It suits large households that need high hot-water volume without consuming interior utility space.
Pros
- Delivers up to 9.5 GPM at a 35°F temperature rise with 199,900 BTU/hr input
- Outdoor wall-mounted installation requires no indoor exhaust venting
- Digital LED panel allows temperature adjustments in 1°F increments
- Built-in freeze protection and flame failure protection
Cons
- Outdoor installation only; not designed for interior utility closets
- Non-condensing design has a 0.82 UEF rating
- This configuration does not include Wi-Fi connectivity
Good fit if
- You need high hot-water volume to run up to four fixtures simultaneously.
- You want an exterior installation to avoid running indoor venting ducts.
- You want precise temperature control down to 1°F adjustments.
Skip if
- You need an indoor water heater.
- You want higher thermal efficiency than a 0.82 UEF non-condensing unit.
Verdict: Rheem RTG 9.5 GPM Outdoor Natural Gas Water Heater provides top-tier flow rates for high-demand homes without requiring interior space or venting pipes.
Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater
Best for: moderate-demand homes needing high condensing efficiency
- Fuel Type
- Natural Gas (what this guide is about)
- 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 Affiliate link
This Rheem RTGH indoor condensing unit runs on natural gas and produces up to 6.8 GPM at a 35°F temperature rise using 120,000 BTU/hr. It features a 0.93 Uniform Energy Factor and direct-vent indoor installation. If you need endless hot water for two to three simultaneous showers in a moderate-demand home, this compact heater gives you precise digital temperature control within 1°F without oversized gas input requirements.
Pros
- 0.93 Uniform Energy Factor (UEF) condensing efficiency
- Flow rate of 6.8 GPM at a 35°F temperature rise
- Digital LED control with ±1°F temperature accuracy
- 15-year heat exchanger and 5-year parts warranty
Cons
- Lacks built-in Wi-Fi connectivity
- Lower peak flow rate than 8.4 GPM and 9.5 GPM alternatives
Good fit if
- You need hot water capacity for up to two or three simultaneous showers.
- You have an indoor space suitable for direct-vent installation.
- You want 0.93 UEF efficiency paired with a 120,000 BTU/hr gas input.
Skip if
- You require an outdoor installation location.
- You want integrated Wi-Fi support for remote controls.
- You need higher flow rates for high-demand simultaneous fixtures.
Verdict: Rheem RTGH Series 6.8 GPM Indoor Tankless Water Heater delivers 0.93 UEF condensing efficiency and up to 6.8 GPM for homes needing reliable two- to three-shower capacity. Its 120,000 BTU/hr rating makes it a practical indoor natural gas option when you do not need the highest flow volumes.
Rheem Prestige 11 GPM Condensing Water Heater
Best for: high-demand indoor homes needing built-in recirculation
- Fuel Type
- Natural Gas (what this guide is about)
- 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 Affiliate link
This Rheem unit is an indoor condensing natural gas tankless water heater designed for high hot-water demand. It delivers a flow rate of 11.0 GPM, making it the highest-capacity option on this 8-pick list. The system includes built-in recirculation with auto-learn programming to track your usage patterns, plus integrated water and gas leak detection. It suits you if you run multiple hot water fixtures simultaneously indoors.
Pros
- High 11.0 GPM maximum flow rate
- Built-in recirculation with auto-learn usage tracking
- Integrated water and gas leak detection with auto-shutdown
- Condensing operation for indoor natural gas hookups
Cons
- Indoor installation only
- Deep 14.8-inch profile requires ample wall clearance
Good fit if
- You need an 11.0 GPM flow rate to supply multiple fixtures at once.
- You want built-in recirculation to manage hot water wait times indoors.
- You require automatic shut-off safety for water and gas leaks.
Skip if
- You need an outdoor-mounted water heater.
- You lack the space for a 28.7 by 17.3 by 14.8 inch enclosure.
Verdict: Rheem 11 GPM Indoor Recirculating Tankless Heater provides maximum flow capacity alongside built-in recirculation for demanding indoor natural gas setups. It serves high-demand indoor households needing integrated scheduling and leak protection.
Rheem IKONIC 8.4 GPM Natural Gas Water Heater
Best for: indoor tank retrofits using existing gas lines
- Fuel Type
- Natural Gas (what this guide is about)
- Flow Rate
- 8.4 GPM
- BTU
- 157,000 BTUs
- Installation Location
- Indoor
- Dimensions
- 28.6 x 17.3 x 13.7 inches
- Weight
- 77.6 pounds
View on Amazon: Rheem IKONIC 8.4 GPM Natural Gas Water Heater Affiliate link
This Rheem IKONIC unit is an indoor condensing natural gas tankless water heater. It delivers up to 8.4 GPM with a 157,000 BTU heating capacity. Its dual heat exchangers maximize heating efficiency, while compatibility with half-inch gas lines and flexible venting simplifies replacing a standard tank. It fits your home if you need reliable whole-house hot water across multiple fixtures simultaneously without upgrading your existing gas lines.
Pros
- Delivers up to 8.4 GPM flow rate with 157,000 BTUs
- Compatible with standard 1/2-inch gas lines for retrofits
- Dual heat exchangers provide condensing operation
- Flexible venting options support room air intake and flex runs
Cons
- Restricted to indoor installations only
- Weighs 77.6 pounds, requiring secure wall mounting
- Built-in recirculation pump not included on this base model
Good fit if
- You need up to 8.4 GPM for multiple simultaneous indoor fixtures.
- You are replacing a storage tank using existing 1/2-inch gas lines.
- You want an indoor condensing unit with a 15-year limited warranty.
Skip if
- You need an exterior outdoor installation.
- You require built-in recirculation integrated directly into the unit.
Verdict: Rheem IKONIC 8.4 GPM Indoor Tankless Heater delivers robust flow for multi-tap households with versatile indoor venting and retrofit-ready gas line sizing.
Rheem 6.8 GPM Outdoor Condensing Water Heater
Best for: Outdoor installations in cold climates
- Fuel Type
- Natural Gas (what this guide is about)
- Flow Rate
- 6.8 GPM
- Installation Location
- Outdoor
- Dimensions
- 28.5 x 9.75 x 27.5 inches
- Venting Type
- Condensing
- Weight
- 77 pounds
View on Amazon: Rheem 6.8 GPM Outdoor Condensing Water Heater Affiliate link
The Rheem Prestige 6.8 GPM Outdoor Tankless Heater is a condensing natural gas unit built for exterior installation. It delivers up to 6.8 GPM of flow and includes built-in freeze protection down to -30 degrees. You also get integrated water and gas leak detection that shuts down the heater and displays an error code. This model suits you if you need moderate flow capacity without indoor venting requirements.
Pros
- Freeze protection rated down to -30 degrees
- Automatic water and gas leak detection with shutdown and error codes
- Condensing natural gas design with 6.8 GPM flow rate
- Outdoor installation eliminates indoor venting runs
Cons
- Designed strictly for outdoor installation
- 6.8 GPM flow rate is lower than 8.4 and 9.5 GPM Rheem options
- Unit weighs 77 pounds
Good fit if
- You want an outdoor natural gas heater with freeze protection down to -30 degrees.
- You need a flow rate of up to 6.8 GPM for your household.
- You want built-in safety shutoffs for water and gas leaks.
Skip if
- You need an indoor water heater installation.
- You require a flow rate higher than 6.8 GPM.
Verdict: Rheem Prestige 6.8 GPM Outdoor Tankless Heater provides reliable outdoor natural gas heating with sub-zero freeze protection and leak shutoff sensors. It serves homes needing up to 6.8 GPM without consuming indoor utility space.
Rheem RTG Outdoor Natural Gas Tankless Water Heater
Best for: outdoor installations needing 8.4 GPM flow
- Fuel Type
- Natural Gas (what this guide is about)
- Flow Rate
- 8.4 GPM
- Installation Location
- Outdoor
- Dimensions
- 23.6 x 13.9 x 13.9 inches
- Weight
- 54 pounds
View on Amazon: Rheem RTG Outdoor Natural Gas Tankless Water Heater Affiliate link
This outdoor natural gas tankless water heater delivers up to 8.4 GPM using 157,000 BTU per hour. It installs outside, saving interior space while handling cold weather with built-in freeze protection down to -30 degrees. Hot Start Programming keeps the system ready to minimize cold-water bursts between uses. It fits your home if you need outdoor flow capacity without indoor venting requirements.
Pros
- Delivers up to 8.4 GPM flow rate
- Freeze protection rated down to -30 degrees
- Hot Start Programming minimizes cold water bursts
- Recirculation pump kit ready
Cons
- Outdoor installation only
- Mid-efficiency design rather than condensing
- Recirculation pump requires a separate kit
Good fit if
- You want an outdoor natural gas heater delivering 8.4 GPM.
- You live in a climate requiring freeze protection down to -30 degrees.
- You want to eliminate cold water bursts using Hot Start Programming.
Skip if
- You require an indoor tankless water heater.
- You prefer a condensing high-efficiency unit.
Verdict: Rheem 8.4 GPM Outdoor Natural Gas Tankless Water Heater provides steady outdoor flow with built-in freeze protection down to -30 degrees and 157,000 BTU output. It is a capable mid-efficiency outdoor option when you want to avoid indoor venting runs.
Rheem Prestige 9.0 GPM Outdoor Tankless Water Heater
Best for: high-demand outdoor natural gas installations
- Fuel Type
- Natural Gas (what this guide is about)
- Flow Rate
- 9.0 GPM
- Installation Location
- Outdoor
- Dimensions
- 28.5 x 9.75 x 27.5 inches
- Venting Type
- Condensing
- Weight
- 77 pounds
View on Amazon: Rheem Prestige 9.0 GPM Outdoor Tankless Water Heater Affiliate link
This Rheem unit is an outdoor natural gas tankless water heater delivering a 9.0 GPM flow rate. Its condensing design provides high-efficiency continuous hot water for your whole home without indoor venting. You get built-in freeze protection rated down to -30 degrees, plus integrated water and gas leak detection that automatically shuts off the unit. It suits your household if you need high capacity mounted outdoors to save interior wall space.
Pros
- 9.0 GPM maximum flow rate supports multiple simultaneous fixtures
- Outdoor freeze protection rated down to -30 degrees
- Automatic shutdown on water or gas leak detection
- Condensing operation for high fuel efficiency
Cons
- Outdoor installation only; not rated for indoor mounting
- Substantial 77-pound weight requires heavy-duty exterior wall support
Good fit if
- You want to free up indoor space by mounting your heater outside.
- You live in a cold climate that requires freeze protection down to -30 degrees.
- You need a 9.0 GPM natural gas supply to run multiple fixtures at once.
Skip if
- You need an indoor-vented water heater installation.
- You lack an exterior natural gas line connection.
Verdict: Rheem Prestige 9.0 GPM Outdoor Tankless Water Heater delivers strong whole-home capacity with condensing efficiency and sub-zero freeze protection. It keeps mechanical equipment outside while providing automated leak detection shutoffs.
Specifications side by side
| Spec | Rheem RTG 9.5 GPM Natural Gas Water Heater | Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater | Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater | Rheem Prestige 11 GPM Condensing Water Heater | Rheem IKONIC 8.4 GPM Natural Gas Water Heater | Rheem 6.8 GPM Outdoor Condensing Water Heater | Rheem RTG Outdoor Natural Gas Tankless Water Heater | Rheem Prestige 9.0 GPM Outdoor Tankless Water Heater |
|---|---|---|---|---|---|---|---|---|
| Fuel Type | Natural Gas | Natural Gas | Natural Gas | Natural Gas | Natural Gas | Natural Gas | Natural Gas | Natural Gas |
| Flow Rate | 9.5 GPM | 9.5 GPM | 6.8 GPM | 11.0 GPM | 8.4 GPM | 6.8 GPM | 8.4 GPM | 9.0 GPM |
| BTU | 199,900 BTU/hr | 199,900 BTU/hr | 120,000 BTU/hr | not stated | 157,000 BTUs | not stated | not stated | not stated |
| Installation Location | Indoor | Outdoor | Indoor | Indoor | Indoor | Outdoor | Outdoor | Outdoor |
| Temperature Control | ±1°F | ±1°F | ±1°F | not stated | not stated | not stated | not stated | not stated |
| Certification | CSA | CSA | CSA | not stated | not stated | not stated | not stated | not stated |
| Dimensions | 24.2 x 13.5 x 10.3 inches | 20.8 x 13.5 x 9.4 inches | 23.7 x 17.7 x 9.8 inches | 28.7 x 17.3 x 14.8 inches | 28.6 x 17.3 x 13.7 inches | 28.5 x 9.75 x 27.5 inches | 23.6 x 13.9 x 13.9 inches | 28.5 x 9.75 x 27.5 inches |
| Venting Type | Non-Condensing | Non-Condensing | not stated | Condensing | not stated | Condensing | not stated | Condensing |
| Features | WiFi | WiFi | WiFi | not stated | not stated | not stated | not stated | not stated |
| Weight | 46.5 pounds | 39.3 pounds | 59.9 pounds | not stated | 77.6 pounds | 77 pounds | 54 pounds | 77 pounds |
| Size | 9.5 GPM (WiFi) | 9.5 GPM (No WiFi) | 6.8 GPM (No WiFi) | 11 GPM | 8.4 GPM | not stated | not stated | not stated |
| Color | Gray | Gray | Gray | Gray | Gray | Gray | Gray | Gray |
| Model | RTG-95DVELN-3 | RTG-95XLN-3 | RTGH-68DVLN-3 | RTGH-RH11DVLN | RECTGH-S84iN | RTGH-68XLN-2 | RTG-84XLN-1 | RTGH-90XLN-2 |
If you plan to run outdoor fuel lines from your meter, review specs for the best natural gas patio heaters.
How to choose the right one
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Check indoor venting needs
Indoor units require specific venting setups. The Rheem RTG 9.5 GPM Indoor Gas Tankless Heater uses a non-condensing design. This means it needs standard vertical vent pipes to exhaust combustion gases. If you install this unit, ensure you have the space for these pipes. Condensing models like the Rheem Prestige 11 GPM use different venting. They are more efficient but may need PVC piping. Match your home’s existing vent structure to the unit’s type to avoid complex retrofits.
-
Select outdoor or indoor fit
Your installation location dictates the model type. Outdoor units like the Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater save interior space. They do not need venting pipes running through your home. However, they must withstand weather. Indoor units like the Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater protect the equipment from elements. They fit in utility rooms or closets. Choose based on whether you have exterior wall space or interior closet space available for the heater.
-
Match flow rate to usage
Flow rate determines how many showers run at once. The Rheem Prestige 11 GPM Condensing Water Heater offers the highest capacity here. It suits large homes with multiple bathrooms running simultaneously. The Rheem RTG 9.5 GPM Indoor Gas Water Heater also supports multi-bathroom use. Smaller households might prefer the Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater. It provides sufficient flow for two to three showers. Check your peak demand to avoid undersizing your unit for daily hot water needs.
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Consider condensing efficiency
Condensing technology extracts more heat from the gas. The Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater delivers 0.93 UEF efficiency. This high rating means lower energy bills for moderate-demand homes. Non-condensing models like the Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater are less efficient. They vent more heat. Choose condensing if you prioritize energy savings and have the budget for the unit. Non-condensing options are often simpler to install where venting is straightforward.
-
Verify smart features
Some models include WiFi monitoring for remote control. The Rheem RTG 9.5 GPM Indoor Gas Tankless Heater offers this feature. You can check status and adjust settings via an app. The outdoor version of the 9.5 GPM model lacks WiFi. It focuses on raw performance. If you want remote diagnostics and scheduling, select the indoor WiFi-enabled unit. If you prefer simplicity and do not need app integration, the non-WiFi outdoor model is a practical choice for your needs.
Frequently asked questions
Which Rheem natural gas tankless water heater has the highest flow rate?
The Rheem Prestige 11 GPM Condensing Water Heater offers the maximum capacity at 11 GPM. It is designed for high-demand indoor households that need integrated scheduling and leak protection. This model uses condensing technology to maximize efficiency while delivering the highest flow volume in this selection.
Do I need venting for outdoor Rheem gas water heaters?
No, outdoor models do not require venting pipes. The Rheem RTG 9.5 GPM Outdoor Natural Gas Tankless Heater and the 6.8 GPM Outdoor Condensing unit are designed for vent-free installation. This allows you to place the mechanical equipment outside without consuming indoor utility space or running vent lines.
Can Rheem tankless water heaters be used in cold climates outdoors?
Yes, several outdoor models include sub-zero freeze protection. The Rheem 6.8 GPM Outdoor Condensing Water Heater and the 8.4 GPM Outdoor Natural Gas Tankless Water Heater both feature built-in freeze protection down to -30 degrees. This ensures reliable operation even in harsh winter conditions without indoor heating.
Which model is best for retrofitting an existing indoor tank?
The Rheem IKONIC 8.4 GPM Natural Gas Water Heater is ideal for indoor tank retrofits. It delivers robust flow for multi-tap households and features versatile indoor venting options. Its design accommodates existing gas line sizing, making it a practical choice when replacing a traditional tank in an indoor location.
Does the Rheem RTG 9.5 GPM Indoor unit have WiFi?
Yes, the indoor version includes WiFi monitoring capabilities. The Rheem RTG 9.5 GPM Natural Gas Water Heater allows you to track performance remotely. This feature is not available on the outdoor counterpart, which delivers the same 9.5 GPM flow rate but lacks wireless connectivity for system management.
Which Rheem gas heater is best for moderate demand homes?
The Rheem RTGH 6.8 GPM Indoor Natural Gas Tankless Heater suits moderate-demand homes. It provides up to 6.8 GPM with 0.93 UEF condensing efficiency. This 120,000 BTU/hr rating supports two to three simultaneous showers, offering a practical indoor solution when you do not require the highest possible flow volumes.