Choosing the best natural gas water heater with power-vent-style exhaust means looking beyond the “tankless” label. A power vent uses a fan to move exhaust, while a direct-vent system may also use a fan but has specific air-intake and venting requirements. Of the models below, the MIZUDO explicitly lists a forced-draft fan; other products describe direct venting or a combustion fan without using the exact term “power vent.” Confirm the venting method and installation requirements for your home before you buy.
The right choice also depends on how much hot water your household uses at once, your incoming water temperature, and whether the unit can be vented safely from its planned location. Here’s how the five natural gas tankless options compare.
| Product | Flow rate | Key features | Best fit |
|---|---|---|---|
| Rheem RTG Series 7.0 GPM | Up to 7.0 GPM | 160,000 BTU; 0.82 UEF; LeakGuard | Homes seeking a whole-house indoor unit |
| MIZUDO 199,000 BTU Tankless | Up to 10.3 GPM | Forced-draft fan; WiFi; 0.53 GPM activation | High demand and app-based controls |
| Westinghouse 5.1 GPM Tankless | Up to 5.1 GPM | 120,000 BTU; WiFi; variable-speed fan | Everyday use in a smaller household |
| Rheem RTGH Series 8.4 GPM | Up to 8.4 GPM | 157,000 BTU; 0.93 UEF; condensing design | Higher efficiency and multi-bathroom use |
| Rinnai RX180iN | Up to 10 GPM | 180,000 BTU; 0.98 UEF; indoor or outdoor use | Flexible installation and high hot-water demand |
Table of Contents
Our Picks: Best Natural Gas Water Heater Power Vent reviews
Rheem RTG Series: A Practical Whole-Home Tankless Option
The Rheem RTG Series is an indoor, non-condensing natural gas tankless heater rated at 160,000 BTU per hour. Its listed maximum flow is 7.0 GPM at a 35°F temperature rise. That gives you a useful starting point for comparing it with other models, though actual flow depends on your water temperature and how much heat the unit must add.
Its wall-mounted design saves floor space, and the digital control lets you set the temperature in 1°F increments. Rheem also lists freeze and flame-failure protection, along with LeakGuard leak detection and prevention. The 0.82 UEF is lower than the condensing Rheem and Rinnai options in this group, so shoppers focused on the highest listed efficiency may prefer those models.
This unit uses an indoor direct-vent system, but the supplied specifications do not identify it specifically as a power-vent model. If a fan-assisted vent is a firm requirement, ask an installer to confirm the exact venting arrangement before ordering. Its combination of whole-home capacity and leak protection may appeal to households replacing a tank heater without moving to a larger-capacity unit.
Pros:
- Up to 7.0 GPM at a 35°F temperature rise
- LeakGuard detection and prevention are included
- Digital temperature adjustment in 1°F increments
- Wall-mounted design frees up floor space
Cons:
- Its 0.82 UEF is below the listed condensing alternatives
- The supplied description does not specify a power-vent fan
Verdict: Choose the Rheem RTG if you want a mid-to-high-capacity indoor tankless heater with built-in leak protection, but verify its venting details if you specifically need power venting.
MIZUDO 199,000 BTU: High Capacity with a Listed Forced-Draft Fan
The MIZUDO is the clearest match in this group for shoppers seeking a fan-assisted vent: its description specifies a bottom-mounted forced-draft fan and a sealed concentric direct-vent system. The unit draws combustion air from outdoors and sends exhaust outside through a dedicated 3-inch by 5-inch concentric vent kit. That arrangement is not a substitute for checking local requirements or confirming the exact vent kit and installation plan.
With 199,000 BTU of input and a listed maximum flow of 10.3 GPM, this model is designed for substantial demand. Its low-flow activation point is listed as 0.53 GPM, and temperature control is adjustable up to 149°F. The WiFi app and Alexa compatibility add remote monitoring and adjustment, while the compact indoor design may fit a closet, basement, or laundry area if clearances and venting allow.
The listed flow rate is a maximum, not a promise that every home will get that output in all conditions. The specifications also say the unit is not recommended above 3,000 feet in elevation, an important limit for some buyers. Its stated warranty covers the full unit for two years and the heat exchanger for five years.
Pros:
- Forced-draft fan and sealed concentric direct-vent system are specified
- High listed capacity of 199,000 BTU and up to 10.3 GPM
- WiFi app control, Alexa compatibility, and abnormal-operation alerts
- Low-flow activation point of 0.53 GPM
Cons:
- Not recommended for elevations above 3,000 feet
- Requires careful planning for its specified concentric vent system
Verdict: The MIZUDO is the strongest fit here if you want an explicitly listed forced-draft fan, high capacity, and smart controls—and your home meets its installation limits.
Westinghouse 5.1 GPM: Smart Controls for Everyday Hot-Water Use
This indoor Westinghouse tankless heater is rated at 120,000 BTU and up to 5.1 GPM. It is the lowest-capacity option in this comparison, so it is worth considering for a home with more modest simultaneous hot-water needs. The supplied product description says it can support multiple fixtures, but the actual number you can run comfortably will depend on flow demand and incoming water temperature.
WiFi and app controls let you adjust the temperature and check operating details, including daily water-use reports. The unit also has an LED panel, temperature control within ±1°F, and an adjustable setting range from 95°F to 149°F. Its variable-speed combustion fan is relevant for shoppers comparing fan-assisted systems, though the listing does not specify the same vent setup as the MIZUDO.
The unit is CSA-certified, uses standard 3/4-inch NPT residential plumbing connections, and requires a 120V AC power source. The description advises draining the system in very cold conditions or during extended periods of non-use. Compared with the higher-output models here, its main trade-off is capacity rather than a lack of connected features.
Pros:
- WiFi app control and water-use reporting
- Variable-speed combustion fan is specified
- Temperature adjustment from 95°F to 149°F
- Compact wall-mounted design
Cons:
- Its 5.1 GPM rating is the lowest in this comparison
- Requires a 120V AC power source and appropriate vent planning
Verdict: Consider the Westinghouse if app control and a smaller listed capacity suit your household, but look at the higher-output options if several fixtures often run at once.
Rheem RTGH Series: A Condensing Model for Higher Efficiency
The Rheem RTGH is an indoor condensing natural gas tankless heater rated at 157,000 BTU per hour. Its listed flow is up to 8.4 GPM at a 35°F temperature rise. The condensing design and 0.93 UEF make it a higher-efficiency choice than the non-condensing Rheem RTG in this comparison, based on the supplied specifications.
Rheem describes this model as suitable for larger households and multiple bathrooms. It includes digital temperature control with 1°F precision, freeze protection, and a multi-point safety system. The product information lists a 15-year heat exchanger warranty and a five-year parts warranty; check the warranty terms and installation requirements before purchase.
The RTGH uses indoor direct venting, but its supplied description does not explicitly identify it as a power-vent model. That distinction matters if you are replacing an existing heater and plan to reuse venting. Condensing units can have different installation needs from non-condensing models, so have a qualified installer confirm compatibility rather than assuming the old vent can be reused.
Pros:
- Up to 8.4 GPM at a 35°F temperature rise
- 0.93 UEF and condensing technology
- Digital temperature adjustment in 1°F increments
- Listed 15-year heat exchanger and five-year parts warranties
Cons:
- The supplied description does not specify a power-vent fan
- Condensing design makes installer confirmation of venting especially important
Verdict: Choose the RTGH if you want a higher-efficiency Rheem with more listed flow than the RTG, provided its venting and installation requirements work for your home.
Rinnai RX180iN: Flexible Placement and High Listed Flow
The Rinnai RX180iN is a condensing tankless heater with 180,000 BTU input and a listed maximum flow of 10 GPM. The description says it can serve up to six fixtures at once, but household results will vary with fixture flow and the temperature rise required. Its 0.98 UEF is the highest listed in this group.
Rinnai describes this model as installable indoors or outdoors, with the required outdoor vent cap for outdoor installation. Its Smart Sense gas control supports either natural gas or propane, while the product listing identifies this version as supporting natural gas. The Quick Flush feature is intended to simplify flushing, and the unit has a built-in interface. WiFi control requires a separate Controlr module, so it is not included as a standard feature in the supplied description.
Professional installation is recommended. The listed residential warranty includes 15 years on the heat exchanger, five years on parts, and five years on labor when the stated registration condition is met; otherwise, the labor warranty defaults to one year. Its flexible placement and high listed output are appealing, but buyers should confirm the correct vent accessories and installation configuration before choosing it.
Pros:
- Up to 10 GPM and 180,000 BTU of input
- Highest listed UEF in this comparison at 0.98
- Can be installed indoors or outdoors with the required configuration
- Quick Flush feature and substantial listed warranty coverage
Cons:
- WiFi control requires a separate Controlr module
- Outdoor installation requires the specified vent cap
Verdict: The Rinnai is a strong option for high demand and flexible placement, especially if its condensing efficiency and professional installation requirements fit your project.
How to Choose a Natural Gas Water Heater with Power Vent
Confirm the vent type, not just the fan
“Power vent” and “direct vent” describe different parts of a venting setup, and product listings may use these terms differently. A power-vent system uses a fan to move exhaust; a direct-vent system describes how combustion air and exhaust are routed. The MIZUDO description specifically lists a forced-draft fan and sealed concentric direct vent. Rheem describes its indoor models as direct vent, while Westinghouse lists a variable-speed combustion fan. Ask the manufacturer or a qualified installer to confirm the exact vent design, compatible materials, and required clearances for your installation.
Size for your peak hot-water demand
Compare the heater’s flow rate with the combined flow of the fixtures you expect to use at the same time. A shower, kitchen faucet, and laundry appliance can all draw hot water at once. The listed maximum GPM alone does not tell you exactly how many fixtures your home can run comfortably, because the unit’s output changes with the temperature rise needed. Consider your household’s busiest periods and have a professional size the heater for your incoming water temperature.
Understand the temperature-rise rating
Some listed flow rates include a specific temperature rise, such as the Rheem RTG and RTGH ratings at 35°F. A colder incoming water supply requires the heater to add more heat, which can reduce the available flow. Use your local incoming water temperature and preferred hot-water setting when comparing models, rather than treating every advertised GPM figure as directly equal.
Compare condensing and non-condensing designs
Condensing models in this group include the Rheem RTGH and Rinnai RX180iN. Their listed UEF values are higher than the non-condensing Rheem RTG’s, but efficiency is only one part of the decision. Condensing and non-condensing models can have different venting and installation needs. Confirm the complete installation plan, including venting, before deciding that a unit is a straightforward replacement.
Check power, gas, and installation requirements
Tankless units may need an electrical connection for controls and fan operation. The Westinghouse description specifies 120V AC power, and installation details for the other models should be checked in their manuals. Have a qualified installer assess the gas supply, plumbing connections, mounting location, vent route, and local code requirements. Do not assume an existing tank-heater setup will work unchanged.
Review controls, service, and warranty terms
WiFi control is built into the MIZUDO and Westinghouse descriptions, while Rinnai’s WiFi option requires a separate module. The Rheem models list digital controls. Compare these features with how you plan to operate and maintain the heater. Read the warranty conditions carefully, including registration requirements and coverage for parts, the heat exchanger, and labor.
Consider climate and periods of non-use
Cold conditions can put a tankless heater at risk if water remains inside the unit. The supplied descriptions call out freeze protection on some models and recommend draining certain units during very cold weather or extended non-use. Follow the model-specific manual for freeze protection, draining, and restart procedures; the correct steps can differ by product and installation.
Frequently Asked Questions
Is a direct-vent water heater the same as a power-vent water heater?
No. Power vent refers to using a fan to move exhaust, while direct vent describes the route for combustion air and exhaust. A unit may use a fan and a direct-vent arrangement, but those terms are not interchangeable. Check the specific product’s venting instructions.
Which model here most clearly specifies a forced-draft fan?
The MIZUDO listing explicitly describes a bottom-mounted forced-draft fan and a sealed concentric direct-vent system. The Westinghouse lists a variable-speed combustion fan, but its supplied description does not specify the same concentric vent setup.
How many showers can these tankless heaters run at once?
There is no fixed number that applies to every home. The answer depends on the model’s output, the incoming water temperature, shower flow, and other fixtures running at the same time. Use the listed GPM as a comparison point and have a qualified professional size the unit for your home.
Does a tankless water heater need electricity?
Some models require an electrical connection for controls and other components. The Westinghouse description specifies a 120V AC power source. Check the installation manual for the exact electrical requirements of the model you are considering.
Can I install one of these heaters myself?
Professional installation is recommended for several models, and gas, venting, plumbing, and code requirements need to be addressed. Have a qualified installer confirm that the unit, vent system, gas supply, and planned location are suitable for your home.
Is a condensing model always the best choice?
Not for every home. The condensing models in this comparison have higher listed UEF values, but you should also consider venting requirements, installation conditions, capacity, warranty terms, and the cost of the full installation. A professional can help compare the options for your setup.
Final Recommendation
For a natural gas tankless heater in this group with the clearest stated power-vent-style feature, the MIZUDO stands out because its description explicitly lists a forced-draft fan and sealed direct vent. The Rinnai RX180iN offers high listed flow and the highest listed UEF, while the Rheem RTGH is a compelling condensing option with a lower listed flow rate. Before choosing any model, confirm the venting method, capacity for your incoming water temperature, and installation requirements with a qualified professional.
