For most homes seeking an indoor natural gas tankless water heater, the Rheem RTGH-84DVLN-3 stands out for its 8.4 GPM capacity and condensing design. The Rinnai RE199iN is another strong option for buyers prioritizing a recognized high-capacity model, while the smaller ThermoMate CZ422NG may suit lighter hot-water demand. The main tradeoffs are flow capacity, installation needs, fuel compatibility, and the added complexity of condensing equipment. A larger GPM figure alone does not tell you how many showers and appliances can run at once in your climate. Read on for the full breakdown and guidance on matching a heater to your home.
Get baby and family essentials delivered free — and shop member deals
- Fast, free delivery on millions of items
- Access to Prime Big Deal Days deals on October 6–7
- Prime Video, Amazon Music and more included
Complete the kit
Key Takeaways
The Rheem RTGH-84DVLN-3 leads this lineup with 8.4 GPM and a condensing design, but its installation needs may be more involved than a non-condensing unit.
Several natural gas models cluster near 199,000 BTU, including GASLAND, MIZUDO, and Rinnai; compare their installation support and verified specifications rather than treating similar input ratings as equal performance.
Compact 4.3 to 5.1 GPM models from VEVOR, Novieex, ThermoMate, and MIZUDO fit more modest demand, but may constrain simultaneous hot-water use.
Fuel labels matter as much as capacity: the VEVOR and Ranein propane models are separate choices from their natural gas counterparts and should not be treated as interchangeable.
Wi-Fi control is a differentiator, not a capacity upgrade. The MIZUDO 120,000 BTU model adds app control, while larger models in the roundup are better suited to higher concurrent demand.
| tankless water heater gas indoor | Heat output | Flow rate | Fuel |
|---|---|---|---|
| VEVOR 4.3 Gal Tankless Gas Wat | 100,000 BTU | 16 L/min | — |
| GASLAND Gasmart E 199,000 BTU | 199,000 BTU | 7.6 GPM | Natural gas |
| Rheem RTGH-84DVLN-3 8.4 GPM Na | 157,000 BTU/hr | 8.4 GPM at 35°F rise | — |
| Rinnai RE199iN Non-Condensing | 199,000 BTU | — | — |
| MIZUDO Natural Gas Tankless Wa | 199,000 BTU | 10.3 GPM | — |
| Rheem RTG Series 7.0 GPM Natur | 160,000 BTU/hr | 7.0 GPM at a 35°F temperature rise | Natural gas |
| APUS Natural Gas Tankless Wate | 140,000 BTU | 6.8 GPM | Natural gas |
| Westinghouse 7.9 GPM Indoor Na | 180,000 BTU | Up to 7.9 GPM | Natural gas |
| ThermoMate CZ422NG Indoor Natu | 113,000 BTU | Up to 5 GPM | Natural gas |
| Novieex Natural Gas Tankless W | 100,000 BTU | Up to 4.3 GPM | Natural gas |
| Ranein Indoor Natural Gas Tank | 190,000 BTU | 8.5 GPM | Natural gas |
| MIZUDO 120,000 BTU Natural Gas | — | — | Natural gas |
| VEVOR 4.3-Gallon Propane Tankl | — | — | Propane |
| Ranein Indoor Propane Tankless | — | 4.3 GPM | Propane |
| APUS Natural Gas Tankless Wate | 95,000 BTU | 4.42 GPM | Natural gas |
More Details on Our Top Picks
VEVOR 4.3 Gal Tankless Gas Water Heater, 100,000 BTU, Indoor Use
VEVOR’s 100,000-BTU output and stated 16 L/min flow make this a smaller-capacity choice among the indoor gas models here. Its ±1°F temperature control and safeguards for flameout, leakage, dry burning, and freezing offer useful control and protection. Compared with the higher-output GASLAND Gasmart E 199, it has less heating capacity, so it is better matched to a modest household than to several simultaneous high-flow uses. The touch panel and LED display make settings visible at the unit, while the standard 1/2-inch NPT connector may simplify plumbing connections. The tradeoff is that indoor installation requires direct venting and professional gas-line work; buyers should also confirm that its capacity suits their climate and peak demand before choosing it for whole-house service.
Pros:- ±1°F temperature control helps limit swings at the tap.
- Multiple listed protections include flameout, leakage, dry-burning, and anti-freeze safeguards.
- LED display and touch panel provide on-unit controls.
- Wall-mounted body measures 6.3 inches deep.
Cons:- Requires indoor direct venting and professional gas-line setup.
- Its 100,000-BTU output is modest beside the 199,000-BTU GASLAND and Rinnai options.
- The listed capacity and flow may not meet heavy simultaneous household demand.
Best for: Smaller households seeking an indoor natural gas heater with straightforward temperature controls and safety features.
Not ideal for: Large households that regularly run several showers or other high-flow fixtures at once; its 100,000-BTU output is below the higher-capacity models in this group.
- Power source:Gas
- Heat output:100,000 BTU
- Flow rate:16 L/min
- Capacity:4.3 gallons
- Maximum temperature:149°F
- Dimensions:13.78 × 21.65 × 6.3 in
- Connector:1/2-inch NPT
- Mount:Wall
Our verdict“Choose the VEVOR for a smaller household that values precise controls and built-in safeguards over the higher capacity of models such as the GASLAND Gasmart E.”
GASLAND Gasmart E 199,000 BTU Natural Gas Tankless Water Heater, 7.6 GPM, Indoor, CE686NG
GASLAND’s 7.6 GPM rating and 199,000-BTU input put it in the higher-capacity tier, while its CSA certification and freeze, overheat, and flameout protections provide clear installation and safety credentials. Compared with the Rheem RTGH-84DVLN-3, it offers a higher listed flow rate, but Rheem provides a higher stated UEF and hot-start programming. GASLAND’s 0.8 UEF is a more modest efficiency figure, and its maximum temperature is 140°F, below the 149°F listed for the VEVOR and MIZUDO. The wall-mounted format keeps it off the floor, but this remains a natural-gas indoor appliance that needs suitable venting and professional installation. It suits buyers prioritizing capacity and certification over extra temperature range or the Rheem’s efficiency-focused feature set.
Pros:- 7.6 GPM flow rating supports multiple fixtures.
- CSA certification is specified for the unit.
- Freeze, overheat, and flameout protections are included.
- Wall-mounted installation saves floor space.
Cons:- Maximum temperature is 140°F, lower than the VEVOR and MIZUDO listings.
- Its 0.8 UEF is below the Rheem RTGH-84DVLN-3’s stated 0.93 UEF.
- Requires natural gas, indoor installation, and appropriate venting.
Best for: Natural-gas households needing a certified indoor unit with capacity for several fixtures and built-in freeze protection.
Not ideal for: Buyers who need water temperatures above 140°F or place a high priority on a higher stated efficiency factor.
- Fuel:Natural gas
- Heat output:199,000 BTU
- Flow rate:7.6 GPM
- UEF:0.8
- Maximum temperature:140°F
- Maximum pressure:150 psi
- Certification:CSA
- Dimensions:14.25 × 24.69 × 7.28 in
Our verdict“Pick the GASLAND when certified, higher-flow natural-gas service matters more than the Rheem’s higher UEF or the VEVOR’s higher maximum temperature.”
Rheem RTGH-84DVLN-3 8.4 GPM Natural Gas Tankless Water Heater, Indoor, 157,000 BTU Condensing Ultra-Low NOx
Rheem pairs an 8.4 GPM rating with a stated 0.93 UEF, making this a strong fit for households balancing multiple hot-water uses with efficiency. Its condensing design, ultra-low NOx certification, and hot-start programming set it apart from the non-condensing Rinnai RE199iN: Rheem emphasizes efficiency and fewer cold bursts between uses, while Rinnai lists a higher maximum flow. Rheem’s 157,000-BTU input is also below the 199,000-BTU GASLAND and Rinnai units, so flow needs depend on incoming water temperature and simultaneous demand. A 15-year heat exchanger warranty and freeze protection add practical reassurance, though installation calls for direct venting and professional work. This is a substantial wall-mounted appliance, not a low-effort swap for every existing heater.
Pros:- Stated 0.93 UEF distinguishes it from the GASLAND’s 0.8 UEF.
- 8.4 GPM rating supports substantial simultaneous demand.
- Hot Start Programming is designed to reduce cold bursts between uses.
- 15-year heat exchanger and 5-year parts warranties are listed.
Cons:- Professional installation and direct venting add complexity.
- 157,000-BTU input is below the 199,000-BTU GASLAND and Rinnai models.
- At 59.9 lb, it is heavier than the GASLAND unit.
Best for: Families with several regular hot-water uses who want a condensing unit with a stated high UEF and hot-start programming.
Not ideal for: Households seeking the highest listed flow rate or a simple DIY replacement without professional direct-vent installation.
- Fuel type:Natural gas
- Heat output:157,000 BTU/hr
- Flow rate:8.4 GPM at 35°F rise
- Energy factor:0.93 UEF
- Installation:Indoor, wall mount, direct vent
- Maximum temperature:140°F
- Certification:CSA certified, Ultra-low NOx
- Warranty:15-year heat exchanger, 5-year parts
Our verdict“Choose the Rheem if its 8.4 GPM rating fits your household and you value its stated efficiency and hot-start feature over the Rinnai’s higher listed flow.”
Rinnai RE199iN Non-Condensing Natural Gas Tankless Water Heater
Rinnai’s listed 9.8 GPM flow is the standout here for buyers expecting several fixtures to run at once. Its 199,000-BTU input matches the GASLAND Gasmart E, but Rinnai lists a higher maximum flow; Rheem’s RTGH-84DVLN-3, meanwhile, has a lower 8.4 GPM rating and a condensing design with a higher stated UEF. The RE199iN is non-condensing, so efficiency-focused buyers may prefer Rheem. Rinnai instead offers an LED display with diagnostic codes and service reminders, plus a 15-year limited heat exchanger warranty. Remote monitoring is available through a separately sold Controlr module, which adds a component for anyone wanting WiFi features. Professional installation by a qualified technician is recommended, and actual flow depends on site conditions.
Pros:- 9.8 GPM maximum flow is higher than the other reviewed models’ listed ratings.
- 199,000-BTU input supports whole-house use.
- LED display provides diagnostic codes and service reminders.
- 15-year limited heat exchanger warranty and 5-year parts warranty are listed.
Cons:- Non-condensing design is less efficiency-focused than the Rheem RTGH-84DVLN-3.
- WiFi monitoring requires the separately sold Controlr module.
- Qualified professional installation is recommended.
Best for: Large natural-gas households that prioritize a high listed flow rate and useful on-unit diagnostics.
Not ideal for: Efficiency-focused buyers who prefer a condensing design, or anyone expecting WiFi monitoring without buying an additional module.
- Fuel type:Natural gas
- Type:Non-condensing tankless water heater
- Maximum flow rate:9.8 GPM
- Heat output:199,000 BTU
- Installation:Indoor, wall-mounted
- Heat exchanger warranty:15-year limited
- Parts warranty:5-year
- WiFi compatibility:Rinnai Controlr module sold separately
Our verdict“Choose the Rinnai for its high listed flow and on-unit diagnostics if you accept a non-condensing design and separate purchase for WiFi monitoring.”
MIZUDO Natural Gas Tankless Water Heater, 199,000 BTU, Indoor
MIZUDO lists 10.3 GPM, the highest flow rating among these five, alongside 199,000 BTU and app control with Alexa compatibility. That gives it a distinct appeal over the Rinnai RE199iN, whose listed maximum is 9.8 GPM and whose WiFi needs a separate module. MIZUDO also offers ±1°F temperature control and a 149°F maximum, above the 140°F limits listed for the GASLAND and Rheem. The tradeoffs are a comparatively short listed warranty—two years for the full unit and five for the heat exchanger—and an elevation limit of 3,000 feet. Its concentric direct vent and 3/4-inch NPT connections call for careful installation planning. Buyers in colder climates also need to drain residual water if the unit will sit unused for an extended period.
Pros:- 10.3 GPM listed flow is the highest among these five products.
- WiFi app control and Alexa compatibility are specified.
- ±1°F temperature control and a 149°F maximum are listed.
- CSA certification and sealed direct-vent combustion are specified.
Cons:- Recommended maximum elevation is 3,000 feet.
- Warranty coverage is two years for the full unit and five years for the heat exchanger.
- Cold-climate users may need to drain residual water during extended periods without use.
Best for: Natural-gas households within the stated elevation limit that want high listed flow, app controls, and a 149°F maximum setting.
Not ideal for: Homes above 3,000 feet elevation, or buyers prioritizing a longer full-unit warranty or minimal installation planning.
- Power source:Natural gas
- Heat output:199,000 BTU
- Flow rate:10.3 GPM
- Low-flow activation:0.53 GPM
- Maximum temperature:149°F
- Venting:3 × 5 in concentric direct vent
- Certification:CSA Certified
- Maximum elevation:3,000 feet
Our verdict“Pick the MIZUDO for its high listed flow and included smart controls if your installation is below 3,000 feet and its warranty terms fit your needs.”
Rheem RTG Series 7.0 GPM Natural Gas Tankless Water Heater, Indoor, Non-Condensing
The Rheem RTG Series makes sense for households that want a known whole-home format with enough stated capacity for two to three showers. Its 160,000 BTU output and 7.0 GPM rating put it ahead of the smaller ThermoMate CZ422NG for simultaneous use, though the Westinghouse offers a higher stated flow rate. The digital control gives temperature adjustments in 1°F increments, while LeakGuard and freeze protection add practical safeguards. The tradeoff is its non-condensing design, which is less efficient than condensing alternatives, and its indoor direct-vent setup needs planning. In colder climates, incoming water temperature can also reduce available flow, so the 7.0 GPM figure may not translate to the same number of simultaneous fixtures year-round.
Pros:- 7.0 GPM rating and 160,000 BTU output suit several simultaneous hot-water uses under suitable conditions
- Digital control adjusts temperature in 1°F increments
- LeakGuard detection and freeze protection provide useful safeguards
- Wall-mounted format uses less floor space than a storage tank
Cons:- Non-condensing construction is less efficient than condensing options in the roundup
- Indoor direct-vent installation adds venting requirements
- Cold incoming water can limit the stated flow and simultaneous use
Best for: Households replacing a tank heater that need moderate whole-home capacity and prefer a wall-mounted indoor natural gas unit with built-in leak and freeze protections.
Not ideal for: Homes in very cold climates with frequent simultaneous hot-water demand, or buyers prioritizing the efficiency of a condensing heater.
- Flow rate:7.0 GPM at a 35°F temperature rise
- Fuel:Natural gas
- Heat output:160,000 BTU/hr
- Energy factor:0.82 UEF, non-condensing
- Installation:Indoor, direct vent, wall mount
- Temperature control:Digital LED panel, ±1°F precision
- Safety:LeakGuard leak detection, freeze protection, flame failure protection
- Certification:CSA certified
Our verdict“Choose the Rheem for a mid-to-large household seeking a well-equipped indoor natural gas unit, provided its non-condensing efficiency and venting needs fit the project.”
APUS Natural Gas Tankless Water Heater, 140,000 BTU, 6.8 GPM, Indoor
The APUS pairs a 6.8 GPM rating with WiFi controls, making it the more connected choice beside the Rheem RTG Series, which has a local digital panel but no listed app control. Its Tuya app supports remote monitoring and smart preheat, and the built-in booster pump is intended to help when multiple fixtures draw hot water. The stated capacity is aimed at two showers and two sinks, but actual performance depends on incoming water temperature and household demand; it has less burner output than the 180,000 BTU Westinghouse. The oxygen-free copper heat exchanger and eight listed safety protections add to its appeal. Buyers should account for the 120V connection and the need to drain the unit in freezing conditions below 41°F.
Pros:- Tuya app provides remote control and monitoring
- Built-in booster pump is designed to support flow across multiple fixtures
- Eight listed safety protections include freeze and overheat protection
- Compact wall-mounted unit weighs 26.9 pounds
Cons:- Requires a 120V electrical connection in addition to natural gas
- Must be fully drained in freezing conditions below 41°F to reduce cracking risk
- Lower 140,000 BTU output than the Westinghouse 180,000 BTU model
Best for: Natural gas households that want app-based temperature management and typically run two showers alongside sinks.
Not ideal for: Homes where the heater may face freezing conditions without a reliable draining routine, or buyers seeking the roundup’s highest stated burner output.
- Flow rate:6.8 GPM
- Fuel:Natural gas
- Heat output:140,000 BTU
- Temperature range:95°F–140°F
- Maximum temperature:140°F
- Connectivity:WiFi control through Tuya app
- Electrical requirement:120 volts, 44 watts
- Dimensions and weight:21.26 × 7.09 × 7.09 inches; 26.9 pounds
- Connections:1/2-inch NPT
Our verdict“Pick the APUS if remote app control matters more than maximum burner capacity and you can protect it from freezing.”
Westinghouse 7.9 GPM Indoor Natural Gas Tankless Water Heater, 180,000 BTU
With the lineup’s highest stated flow among these five, the Westinghouse 7.9 GPM model is the strongest fit for homes that regularly run several hot-water fixtures together. Its 180,000 BTU burner gives it more stated capacity than the Rheem RTG Series and ThermoMate CZ422NG, while WiFi and voice control make temperature changes and fault alerts accessible remotely. Low-flow activation at 0.53 GPM and operation from 15 PSI may also suit older plumbing or a well system. Those capabilities come with practical requirements: it needs a 120V outlet and 3/4-inch NPT plumbing, and the listed full-unit warranty is only two years. I would favor it for capacity and connectivity, not for buyers who want simpler installation or longer unit coverage.
Pros:- 7.9 GPM and 180,000 BTU offer the highest stated capacity in this five-product batch
- Built-in WiFi supports app and voice control without an add-on
- Activates at 0.53 GPM and lists a 15 PSI minimum water pressure
- Self-modulating control is specified to hold temperature within ±1°F
Cons:- Requires 120V AC power and professional natural gas installation
- Two-year limited warranty on the unit is shorter than the five-year heat exchanger coverage
- 3/4-inch NPT plumbing connections may require adapting existing lines
Best for: Larger households with multiple simultaneous hot-water draws, especially those with lower-pressure plumbing that want connected controls.
Not ideal for: Buyers without a nearby 120V outlet, homes with incompatible plumbing connections, or anyone prioritizing a longer full-unit warranty.
- Flow rate:Up to 7.9 GPM
- Fuel:Natural gas
- Heat output:180,000 BTU
- Minimum activation flow:0.53 GPM
- Minimum water pressure:15 PSI
- Temperature stability:±1°F
- Connectivity:Built-in WiFi, app and voice control
- Connections and power:3/4-inch NPT; 120V AC
- Warranty:2 years limited on unit; 5 years on heat exchanger
Our verdict“Choose the Westinghouse when simultaneous demand and connected controls outweigh installation requirements and the shorter unit warranty.”
ThermoMate CZ422NG Indoor Natural Gas Tankless Water Heater, 5 GPM
The ThermoMate CZ422NG is a more modest-capacity indoor option for buyers who need less hot water at once than the Westinghouse or Rheem can supply. Its stated 5 GPM and 113,000 BTU output make it better suited to smaller households, while the compact wall-mounted body and diagnostic LED can help keep an installation footprint and basic troubleshooting manageable. ThermoMate lists thermal efficiency up to 98%, though its separate UEF figure is 0.81, so buyers should compare efficiency claims carefully rather than treating those measures as interchangeable. It includes freeze protection and a copper heat exchanger, but still needs compatible gas, electrical, water, and vent connections. The flow figure depends on operating conditions, so it is not the best match for frequent multi-shower use.
Pros:- Compact wall-mounted design measures 13.77 inches wide and 7 inches deep
- Diagnostic LED display provides error codes
- Freeze protection and multiple safety protections are included
- Lists both up-to-98% thermal efficiency and a 0.81 UEF
Cons:- 5 GPM capacity is below the Rheem and Westinghouse models for simultaneous demand
- Actual flow depends on operating conditions and incoming water temperature
- Indoor installation requires compatible gas, electrical, plumbing, and vent connections
Best for: Smaller households seeking a compact indoor natural gas heater for one or two hot-water draws at a time.
Not ideal for: Families that commonly run several showers together or buyers who need a heater with stronger stated flow capacity.
- Flow rate:Up to 5 GPM
- Fuel:Natural gas
- Heat output:113,000 BTU
- Efficiency:Up to 98% thermal efficiency; 0.81 UEF
- Temperature range:90°F–140°F
- Water connections:3/4-inch NPT inlet and outlet
- Vent connection:3-inch OD
- Dimensions and weight:13.77 × 21.65 × 7 inches; 22 pounds
- Certification:CSA certified
Our verdict“The ThermoMate suits space-conscious smaller households, but higher-demand homes should look to the Rheem or Westinghouse.”
Novieex Natural Gas Tankless Water Heater, 4.3 GPM, 100,000 BTU, Indoor
The Novieex is the lowest-capacity choice in this group, aimed at homes with one main hot-water draw and occasional overlap rather than multiple showers. Its stated 4.3 GPM and 100,000 BTU output sit below the ThermoMate CZ422NG’s 5 GPM and 113,000 BTU, making the ThermoMate the safer comparison for households with somewhat broader demand. Novieex’s digital touchscreen and ±1°F temperature control give users precise adjustment across a 95°F–149°F range, and its wall-mounted format frees floor space. The listed 1/2-inch NPT fittings and 110V–120V power requirement still need to match the installation. Its one-year warranty is short, and the stated altitude recommendation caps use at 2,000 feet.
Pros:- 100,000 BTU output supports a shower plus limited simultaneous fixture use under suitable conditions
- Digital touchscreen provides temperature adjustment within ±1°F
- 95°F–149°F temperature range accommodates a broad set point range
- Wall-mounted design saves floor space compared with a storage tank
Cons:- 4.3 GPM capacity is lower than the ThermoMate CZ422NG and larger models in this group
- Listed one-year warranty is limited
- Not recommended for use above 2,000 feet altitude
Best for: Smaller homes with natural gas service that typically use a shower and one additional fixture, and have installation below 2,000 feet.
Not ideal for: Larger families with overlapping showers, homes above the recommended altitude, or buyers seeking longer listed warranty coverage.
- Flow rate:Up to 4.3 GPM
- Fuel:Natural gas
- Heat output:100,000 BTU
- Installation:Indoor, wall mounted
- Temperature range:95°F–149°F
- Temperature control:±1°F accuracy
- Connections:1/2-inch NPT gas inlet and water fittings
- Power:110V–120V AC, 60Hz
- Altitude recommendation:Maximum recommended altitude: 2,000 feet
Our verdict“Choose the Novieex for modest hot-water demand and a compact installation below 2,000 feet, but step up to the ThermoMate for more capacity.”
Ranein Indoor Natural Gas Tankless Water Heater, 8.5 GPM, 190,000 BTU
For a natural gas indoor unit aimed at several fixtures at once, the 8.5 GPM capacity and 190,000 BTU output give this Ranein a broader flow target than the 5.1 GPM MIZUDO. Its wall-mounted body and LED display keep the setup relatively compact and make status checks straightforward. The adjustable blower is described as reducing noise while supporting combustion, though the listing gives no decibel figure for comparison. That higher capacity comes with a major location constraint: Ranein says this model is not recommended above 2,000 feet. It also needs winter draining if left unused in cold weather. This is my pick for suitable low-altitude homes with heavier simultaneous demand; buyers needing app controls or a less restrictive altitude range should compare the MIZUDO instead.
Pros:- 8.5 GPM flow rate and 190,000 BTU output target multi-outlet household demand.
- Wall-mounted design uses less floor space than a storage tank.
- LED display provides a visible interface for unit status.
- Adjusting blower is described as supporting combustion while reducing noise.
Cons:- Not recommended for installation above 2,000 feet.
- Needs draining through the pressure relief valve if left unused in cold weather.
Best for: Low-altitude households that regularly run several hot-water outlets at once and want a high-flow natural gas indoor unit.
Not ideal for: Homes above 2,000 feet or owners who need remote app controls and energy monitoring.
- Fuel:Natural gas
- Flow rate:8.5 GPM
- Heat output:190,000 BTU
- Maximum temperature:155 °F
- Maximum pressure:116 psi
- Dimensions:15.08 × 24.25 × 8.07 in
- Weight:42 lb
- Recommended outlets:4–6
- Altitude guidance:Not recommended above 2,000 ft
Our verdict“Choose this Ranein for high simultaneous demand at low altitude, and look to the lower-flow MIZUDO if app control matters more.”
MIZUDO 120,000 BTU Natural Gas Tankless Water Heater, Max 5.1 GPM, WiFi & App Control
The MIZUDO stands apart in this group by pairing WiFi app control with a stated temperature stability of within 1°F. Remote adjustments and energy monitoring may suit owners who want to manage settings from a phone, while its 5.1 GPM rating targets a smaller demand envelope than the 8.5 GPM Ranein. Its safety list includes freeze and dry-burn protection, and the copper heat exchanger has a longer stated warranty than the unit warranty. Indoor installation has a specific requirement: a 3-inch OD vent pipe, and the pipe system adds installation complexity. Outdoor use also depends on a separately sold conversion kit. I’d put it ahead of simpler controls-focused models for connected households, but buyers with many simultaneous fixtures should compare its flow rating carefully with the higher-capacity Ranein.
Pros:- WiFi app provides remote temperature adjustment and energy monitoring.
- Rated temperature stability is within 1°F.
- CSA-certified safety features include freeze and dry-burn protection.
- Five-year heat exchanger warranty exceeds the two-year full-unit warranty.
Cons:- Indoor installation requires a specified 3-inch OD vent pipe system.
- Outdoor installation requires a conversion kit sold separately.
- At 5.1 GPM, it has less stated flow capacity than the 8.5 GPM Ranein.
Best for: Natural gas households with moderate simultaneous demand that want app-based temperature adjustments and energy monitoring.
Not ideal for: Buyers seeking the highest flow capacity or an indoor setup without a specified 3-inch vent system and related accessories.
- Fuel:Natural gas
- BTU output:120,000 BTU
- Maximum flow rate:5.1 GPM
- Installation:Indoor or outdoor with conversion kit
- Indoor vent requirement:3-inch OD vent pipe
- Temperature stability:Within 1°F
- Certification:CSA certified
- Connectivity:WiFi with mobile app
- Warranty:2 years full unit; 5 years heat exchanger
Our verdict“Pick the MIZUDO if app control and tight temperature stability matter more than the greater flow capacity of the Ranein.”
VEVOR 4.3-Gallon Propane Tankless Water Heater, 100,000 BTU/h
This VEVOR is the propane option here for buyers who value touch controls and clearly stated temperature accuracy over natural gas compatibility. Its sensors are rated to hold the set temperature within ±1°F, and the LED display makes the setting visible at the unit. Compared with the natural gas APUS 4.42 GPM, this model’s listed data emphasizes a 100,000 BTU/h input and 4.3-gallon capacity rather than a flow rate, so I can’t make a direct GPM comparison from the supplied specifications. The tradeoff is fuel and venting: it requires propane, and indoor installation needs a direct vent. The listing does not provide a warranty, dimensions, or a rated flow figure, which leaves buyers with less information for sizing than the Ranein propane model.
Pros:- Temperature accuracy is specified as ±1°F.
- LED display and touch controls offer a direct way to adjust settings.
- Multiple safety protections are included.
- On-demand operation avoids tank preheating.
Cons:- Requires propane rather than natural gas.
- Indoor installation requires a direct vent connection.
- Supplied specifications do not state a flow rate or warranty.
Best for: Propane-equipped households seeking an indoor unit with touch controls, LED readout, and stated temperature accuracy.
Not ideal for: Natural gas homes or buyers who need a published GPM rating and detailed sizing information before choosing.
- Fuel:Propane
- Capacity:4.3 gallons
- Heating input:100,000 BTU/h
- Temperature accuracy:±1°F
- Display:LED
- Controls:Touch controls
- Installation connector:1/2-inch NPT
- Installation:Indoor; direct vent required
Our verdict“Consider this VEVOR for a propane setup where touch controls matter, but compare its limited sizing data with the Ranein propane model first.”
Ranein Indoor Propane Tankless Water Heater, 4.3 GPM, 100,000 BTU
Among the propane choices, this Ranein gives buyers more explicit household-use guidance: it is rated for 4.3 GPM and 3–4 water points, with presets for kitchen, bathtub, shower, and seasonal use. That makes it easier to match settings to common routines than the VEVOR, whose supplied information highlights touch controls but does not state a flow rate. Its oxygen-free copper heat exchanger and anti-freeze protection down to 14°F add useful detail, though the protection has limits: in colder conditions or extended disuse, draining may still be needed. The unit also carries a 2,000-foot elevation limit and requires licensed professional installation. I’d favor it for propane households that want preset operation and a stated flow rating, while buyers wanting natural gas should look at the APUS instead.
Pros:- 4.3 GPM rating and support for 3–4 water points clarify its intended demand.
- Four presets cover seasonal, kitchen, bathtub, and shower use.
- Anti-freeze protection is rated down to 14°F/-10°C.
- Vent pipe is included.
Cons:- Licensed professional installation is required.
- Not suitable above 2,000 feet elevation.
- May need draining when temperatures fall below its stated anti-freeze range.
Best for: Low-altitude propane households that want defined preset modes and a published flow rating for several water points.
Not ideal for: Homes above 2,000 feet, DIY installers, or households already set up for natural gas.
- Fuel:Propane
- Installation:Indoor
- Flow rate:4.3 GPM
- Heating capacity:100,000 BTU
- Simultaneous water points:3–4
- Temperature range:95°F–155°F
- Heat exchanger:Oxygen-free copper
- Anti-freeze protection:Resists temperatures down to 14°F/-10°C
- Elevation guidance:Not for elevations above 2,000 ft
Our verdict“Choose this Ranein for preset-based propane use at low elevation, and choose the natural gas APUS if fuel compatibility is the priority.”
APUS Natural Gas Tankless Water Heater, 95,000 BTU, 4.42 GPM, Indoor
The APUS is the compact natural gas choice for households whose hot-water pattern fits its 4.42 GPM rating. Its listed capacity covers two showers and a sink, while a low-flow start of 0.66 GPM may help it activate with modest demand. The 19.2-pound wall-mounted body is notably lighter than the 42-pound, 8.5 GPM Ranein, making the APUS the more space-conscious fit; the Ranein is better suited to heavier simultaneous use. APUS also lists ±1°F temperature stability, a touchscreen, and 36 dB operation. The tradeoff is its lower 95,000 BTU output and 140°F maximum setting, below the Ranein’s stated 155°F. It still needs professional gas and electrical connections, and draining is advised before freezing conditions or extended disuse.
Pros:- 4.42 GPM rating is stated to support two showers and a sink.
- Compact 19.2-pound wall-mounted design.
- Temperature stability is specified at ±1°F with a 0.66 GPM low-flow start.
- 36 dB operation and freeze protection are listed.
Cons:- 95,000 BTU output is substantially lower than the high-flow Ranein’s 190,000 BTU.
- Maximum temperature is 140°F, below the Ranein’s 155°F.
- Professional natural gas and 120V electrical connections are required; draining is advised before freezing conditions or long disuse.
Best for: Space-conscious natural gas households with moderate demand that want a light wall-mounted unit and precise temperature control.
Not ideal for: Large households with frequent high simultaneous demand or buyers who need a maximum setting above 140°F.
- Fuel:Natural gas
- Heat output:95,000 BTU
- Flow rate:4.42 GPM
- Low-flow start:0.66 GPM
- Temperature range:95°F–140°F
- Temperature stability:±1°F
- Dimensions:20.55 × 13.27 × 5.91 in
- Weight:19.2 lb
- Noise level:36 dB
Our verdict“Pick the APUS for a compact natural gas installation with moderate demand, and choose the higher-output Ranein if several outlets often run together.”
How We Picked
I ranked these heaters around the decisions that shape an indoor gas installation: fuel type, stated flow and BTU capacity, intended household demand, venting and drainage requirements, and the practical value of controls. Higher-capacity natural gas models rank ahead for households that need to serve multiple fixtures, while smaller units earn a place for compact homes or limited demand. Condensing designs can use gas efficiently, but their venting and condensate handling add installation considerations, so capacity alone did not determine placement.
I also treated natural gas and propane products as distinct options, since fuel compatibility can rule a heater out before any other feature matters. The ranking favors products whose stated specifications suggest a clear role and considers tradeoffs such as lower flow, less installation flexibility, or added setup complexity. Product listings do not establish sizing for a particular home; local inlet water temperature, gas supply, vent route, and applicable codes still need professional review.
| tankless water heater gas indoor | Fuel |
|---|---|
| VEVOR 4.3 Gal Tankless Gas Wat | — |
| GASLAND Gasmart E 199,000 BTU | Natural gas |
| Rheem RTGH-84DVLN-3 8.4 GPM Na | — |
| Rinnai RE199iN Non-Condensing | — |
| MIZUDO Natural Gas Tankless Wa | — |
| Rheem RTG Series 7.0 GPM Natur | Natural gas |
| APUS Natural Gas Tankless Wate | Natural gas |
| Westinghouse 7.9 GPM Indoor Na | Natural gas |
| ThermoMate CZ422NG Indoor Natu | Natural gas |
| Novieex Natural Gas Tankless W | Natural gas |
| Ranein Indoor Natural Gas Tank | Natural gas |
| MIZUDO 120,000 BTU Natural Gas | Natural gas |
| VEVOR 4.3-Gallon Propane Tankl | Propane |
| Ranein Indoor Propane Tankless | Propane |
| APUS Natural Gas Tankless Wate | Natural gas |
Factors to Consider When Choosing Tankless Water Heater Gas Indoor
Choosing an indoor gas tankless heater starts with the conditions in your home, not the biggest number on a product listing. These factors can help narrow the field before you compare individual models.
Size for Your Coldest Inlet Water
A heater’s advertised flow rate does not represent the same usable output in every location. Colder incoming water requires a greater temperature rise, which reduces the flow the unit can deliver at a comfortable set temperature. List the fixtures likely to run together, such as a shower and dishwasher, then use local winter inlet-water temperatures to estimate the demand. A household in a cold climate may need a larger unit than a household with the same fixtures in a warm region. Avoid choosing by bathroom count alone, since showerheads and appliance draws vary. Ask an installer to size from simultaneous flow and temperature rise before purchasing.
Confirm Fuel and Gas Supply
Natural gas and propane models are designed for different fuel supplies, and the product name should match the utility or tank serving your home. Do not assume that a conversion kit is included or that conversion is permitted; check the manufacturer’s instructions and have a qualified installer confirm compatibility. The heater also needs enough gas volume at the required pressure, which can depend on pipe size, pipe length, and other appliances running at the same time. A high-BTU unit may call for gas-line work even when the home already has a gas furnace or range. Include that supply check in the installation quote. Buying the right capacity with an undersized gas line can leave the system unable to deliver its expected output.
Compare Venting and Condensate Needs
Indoor units need a vent route approved for their specific design, and existing water-heater venting may not be suitable. Condensing models can recover more heat from exhaust, but they produce acidic condensate that needs a drain and may need treatment under local rules. Non-condensing models avoid that condensate setup, yet their venting clearances and materials still need to meet the manual and local code. Check where the vent can terminate, how far it must run, and whether the route passes through finished spaces. These details can affect installation scope more than small differences in listed flow rate. Have the installer inspect the proposed location before you commit to a model.
Plan for Electrical Power and Controls
Many gas tankless heaters need electricity for ignition, controls, or fans, so a gas connection alone may not be enough. Verify the voltage and outlet requirements, and ask what happens during a power outage in your area. App control, such as the feature listed on the 120,000 BTU MIZUDO, can make settings easier to check, but it does not increase hot-water output or replace routine service. Decide whether remote monitoring solves a real need in your household before paying attention to it as a deciding feature. Also check how clearly the controls show fault codes and temperature settings. Straightforward diagnostics can help an owner communicate a problem to a service technician.
Account for Maintenance and Service Access
Tankless heaters need periodic maintenance, with the schedule shaped by water hardness, use, and the manufacturer’s directions. Hard water can leave scale inside the heat exchanger and reduce performance, so ask whether your water needs treatment or more frequent flushing. Leave enough clearance to reach service valves and components; a cramped closet can turn routine work into a larger job. Check for local technicians familiar with the specific brand and model before ordering, since service access can matter over the heater’s life. Compare warranty terms and required maintenance records alongside the initial specifications. A model that is easy to maintain may suit a busy household better than one with extra controls but limited service support.
Frequently Asked Questions
How do I know whether a 4.3 to 5 GPM model can handle my household?
Start by adding the flow rates of the fixtures you expect to use at the same time, rather than counting every fixture in the house. Then check the heater’s output at the temperature rise needed where you live, since colder incoming water can lower delivered flow. A compact model may work well for one bathroom or staggered use, but it can struggle when multiple showers run together. Ask an installer to compare your peak demand with the manufacturer’s performance data. If you regularly use several hot-water fixtures at once, a higher-capacity model may be a better fit.
Can I replace my existing gas tank water heater with any indoor tankless model?
No single listed feature confirms that a replacement will fit your installation. The new unit may require different vent materials and routing, a larger gas line, nearby electrical power, or condensate drainage. Its location also needs to meet clearance and service-access rules. Have a qualified installer inspect the gas supply, vent path, and mounting location before selecting a specific heater. That review can reveal whether the project needs upgrades beyond removing the old tank.
Should I choose a condensing or non-condensing heater?
A condensing design extracts more heat from exhaust, which can reduce fuel use under suitable operating conditions, but it needs a condensate drain and compatible vent setup. A non-condensing model avoids condensate disposal, though its vent requirements still need careful planning. The better fit depends on your existing vent route, drainage access, local code, and installation quote. Compare the full installed system requirements rather than the heater alone. The Rheem RTGH-84DVLN-3 is the roundup’s condensing high-capacity pick, while the Rinnai RE199iN is listed as non-condensing.
Are the propane models in this roundup alternatives to the natural gas models?
They are alternatives only if your home is set up for the listed fuel. The VEVOR and Ranein propane models should be compared with other propane-compatible equipment, not assumed to work on a natural gas line. Fuel conversion should happen only if the manufacturer permits it and a qualified professional performs the required work. Check the exact model documentation, fuel input, and installation instructions before ordering. If your home has natural gas, choose a model explicitly specified for natural gas unless a permitted conversion is confirmed.
Does app control make the MIZUDO 120,000 BTU model a better choice than a higher-capacity heater?
App control can make it easier to view or adjust settings, but it does not add BTU input or increase the heater’s available flow. If several fixtures run at once in your home, sizing and temperature-rise performance matter more than remote access. The MIZUDO’s listed 5.1 GPM maximum points to a more modest demand profile than the roundup’s high-capacity options. Choose it when its output matches your measured demand and the app feature is useful to you. If capacity is the limitation, compare a larger model instead.
Conclusion
Best overall: I’d start with the Rheem RTGH-84DVLN-3 for homes needing substantial flow and able to support its condensing installation. Best value: the ThermoMate CZ422NG is a more modest-capacity choice for buyers whose demand does not call for a large unit. Best premium: the Rinnai RE199iN suits shoppers looking for a high-capacity natural gas model from an established manufacturer. Best for beginners: I’d point first-time tankless buyers toward the Rheem RTG Series 7.0 GPM non-condensing model if its capacity fits and local service is available. For specific needs, consider the MIZUDO 120,000 BTU unit for app control, or choose the VEVOR or Ranein propane option only when propane is your home’s fuel. Before buying, have an installer confirm sizing, gas supply, venting, and code requirements for your location.
Fall Picks
fall essentials
As an affiliate, we earn on qualifying purchases.
