A gas tankless water heater can save space and provide hot water on demand, but choosing the right model depends on more than its maximum flow rate. Your incoming water temperature, number of fixtures, gas supply, and installation location all affect how well a unit serves your home. These five natural-gas models range from compact, lower-capacity options to higher-output units designed for several fixtures at once.
Use the comparison below as a starting point, then check the product listing and installation requirements before you buy. Maximum GPM is not a promise of that flow under every condition: colder incoming water requires more heating, which can reduce the available hot-water flow.
| Product | Maximum output | Installation type | Standout detail |
|---|---|---|---|
| GASLAND Gasmart C | 150,000 BTU; 5.8 GPM | Wall-mounted; confirm location requirements | Compact design; listing availability may vary |
| GASLAND Gasmart E | 199,000 BTU; 7.6 GPM | Indoor | CSA certified; freeze and overheat protection |
| MIZUDO Natural Gas Tankless Water Heater | 120,000 BTU; 5.1 GPM | Indoor or outdoor with required accessory kit | Wi-Fi and app controls |
| Westinghouse Outdoor Gas Tankless Water Heater | 180,000 BTU; 8.1 GPM | Outdoor | CSA certified; designed for outdoor operation |
| FOGATTI Natural Gas Tankless Water Heater | 170,000 BTU; 7.5 GPM | Indoor | CSA certified; listed temperature stability of ±1°F |
Table of Contents
Our Picks: Best Whole House Tankless Water Heater Gas reviews
1. GASLAND Gasmart C: A Compact Option for Moderate Hot-Water Demand
The GASLAND Gasmart C is a natural-gas, wall-mounted tankless water heater rated at 150,000 BTU and up to 5.8 GPM. Its compact design may appeal if you want to free up floor space compared with a traditional tank. The listed output is a better fit for measured household demand than for assuming several high-flow fixtures can run at full capacity at the same time.
The manufacturer describes it as energy efficient and says it has a UEF of 0.8. Actual energy use and hot-water output depend on your household and installation. The product data supplied for this model also indicates it may not be available, so check the listing before planning a purchase or installation.
Compared with the higher-output GASLAND Gasmart E, the C has lower BTU and GPM ratings. That may be enough for a smaller household or less simultaneous use, but it leaves less headroom for multiple showers and appliances. Confirm the required gas supply, venting, and installation location with a qualified installer.
Pros:
- Compact wall-mounted design
- Rated up to 5.8 GPM and 150,000 BTU
- Manufacturer lists a UEF of 0.8
Cons:
- Lower maximum output than the GASLAND Gasmart E and several alternatives here
- Listing availability may vary
Verdict: Consider the Gasmart C if its capacity matches your household and you confirm it is available, but choose a higher-output model if you regularly run several hot-water fixtures at once.
2. GASLAND Gasmart E: Higher Output with Built-In Safety Features
The indoor GASLAND Gasmart E is the highest-output model in this group by BTU rating. It is rated at 199,000 BTU and up to 7.6 GPM, giving it more listed capacity than the Gasmart C. It is CSA certified and includes stated protections for overheating, flame-out, and freezing.
The manufacturer lists a UEF of 0.8 and describes the unit as compact and wall-mounted. Those features may suit a home where indoor installation is preferred and several hot-water uses overlap. Still, the maximum flow rate depends on water conditions, so compare its output with your local winter inlet-water temperature and your expected simultaneous demand.
This is a stronger candidate than the lower-output options for a busy household, but it is not automatically the right choice for every home. You will need to confirm that the gas line, venting, electrical connection, and installation space meet the unit’s requirements. The supplied product information describes a replacement promise for failures within a year; review the full warranty terms before relying on that coverage.
Pros:
- Highest listed BTU capacity among these five models
- Up to 7.6 GPM listed flow rate
- CSA certified with several stated safety protections
- Indoor wall-mounted design
Cons:
- Indoor installation requires suitable venting and space
- Actual flow may be lower than the maximum rating, especially with colder incoming water
Verdict: The Gasmart E is a strong option to investigate if you want an indoor model with higher listed capacity and built-in protections, provided your home can support its installation requirements.
3. MIZUDO Natural Gas Tankless Heater: App Controls and Flexible Placement
The MIZUDO is rated at 120,000 BTU and up to 5.1 GPM. Its defining feature is app-based control: the product description says you can adjust temperature settings, monitor energy use, and receive maintenance notifications remotely. That can be useful if you want to manage settings without going to the heater, though it is not a substitute for correct sizing or installation.
This model is described as convertible for indoor or outdoor use, but the required accessory kit must be purchased separately. It is CSA certified and includes stated protections such as freeze protection, dry-burn prevention, flame-failure detection, and exhaust-blockage protection. The manufacturer also specifies a two-year full-unit warranty and five-year heat-exchanger coverage.
At 5.1 GPM, the MIZUDO has the lowest listed maximum flow in this comparison. Its description says it can serve multiple bathrooms, but the rating is modest beside the Westinghouse, GASLAND E, and FOGATTI models. Consider it for a smaller household or a home with limited overlapping hot-water use, and verify whether the accessory kit and installation setup fit your plans.
Pros:
- Wi-Fi and app controls for temperature settings and energy monitoring
- Indoor or outdoor configuration with the required accessory kit
- CSA certified with multiple stated safety protections
- Specified two-year unit and five-year heat-exchanger warranty coverage
Cons:
- Lowest listed maximum flow rate in this group
- Indoor-to-outdoor conversion requires an additional kit
Verdict: Choose the MIZUDO if app controls and installation flexibility matter more to you than maximum flow, and make sure you include the required conversion kit if needed.
4. Westinghouse Outdoor Tankless Heater: Highest Listed Flow for Outdoor Installation
This Westinghouse model is designed for outdoor installation and has the highest listed flow rate in this comparison at up to 8.1 GPM. Its 180,000 BTU rating is also substantial. The manufacturer says it can support three to five fixtures at once, but your real-world results will depend on incoming water temperature, fixture flow, and the system’s installation.
The unit is CSA certified and includes stated freeze protection. Its description also lists a variable-speed combustion fan and temperature control within ±1°F. The installation notes call for standard 3/4-inch NPT residential plumbing connections and 120V AC power, so an outdoor location alone does not mean the unit is free of electrical or plumbing requirements.
Compared with the indoor GASLAND E and FOGATTI, the Westinghouse may be a better fit if an outdoor installation is your priority and your home needs higher flow. The trade-off is that you need an appropriate outdoor location and must follow the manufacturer’s requirements for weather exposure and installation. It comes with stated warranty coverage of two years for the complete unit and five years for the heat exchanger.
Pros:
- Highest listed flow rate in this comparison at 8.1 GPM
- Outdoor design can keep the main unit outside the living area
- CSA certified with stated freeze protection
- Specified two-year unit and five-year heat-exchanger warranty coverage
Cons:
- Requires a suitable outdoor installation location
- Needs 120V AC power as well as compatible plumbing connections
Verdict: The Westinghouse is a compelling outdoor option if you need a high listed flow rate and can meet its electrical, plumbing, and placement requirements.
5. FOGATTI Indoor Tankless Heater: Balanced Output and Precise Temperature Control
The indoor FOGATTI is rated at 170,000 BTU and up to 7.5 GPM. It sits between the GASLAND E and Westinghouse in listed output, making it worth considering if you want an indoor unit with more capacity than the 5.1-GPM MIZUDO or 5.8-GPM GASLAND C. The product description says its controls aim to keep temperature variation within ±1°F.
The manufacturer lists a copper heat exchanger, a 304 stainless-steel burner, CSA certification, and a four-stage combustion system. It also states that the unit can work with water pressure from 15 to 150 PSI and requires a standard 120V AC connection. Its stated warranty covers the complete unit for two years and the heat exchanger for five years.
Pay attention to the operating guidance: the manufacturer recommends using the unit below 2,000 feet in altitude. Its active anti-freeze feature is not a reason to leave water inside during a long period of non-use or in very cold conditions; the product information advises draining the unit if the temperature drops below 5°F or it will sit unused for a long time. Confirm those limits and procedures for your installation.
Pros:
- Up to 7.5 GPM and 170,000 BTU listed capacity
- CSA certified with stated temperature-control features
- Specified operating water-pressure range of 15 to 150 PSI
- Specified two-year unit and five-year heat-exchanger warranty coverage
Cons:
- Manufacturer recommends use below 2,000 feet in altitude
- Requires attention to draining guidance during extended non-use or severe cold
Verdict: The FOGATTI is a good indoor candidate if its output suits your home and you can follow the altitude, electrical, and freeze-protection guidance.
How to Choose a Whole-House Gas Tankless Water Heater
Size the unit for your peak hot-water demand
Start by listing the hot-water fixtures and appliances you might use at the same time. A shower, dishwasher, and sink running together can demand more hot water than one fixture alone. Compare that combined demand with the heater’s capacity, but do not treat the advertised maximum GPM as guaranteed output. The heater must raise incoming water to your selected temperature, and colder incoming water takes more heating power.
Consider BTU output and incoming water temperature together
BTU ratings indicate heating capacity, while GPM describes flow. Neither number tells the whole story by itself. If your incoming water is cold, a heater may provide less flow at a comfortable hot-water temperature than it can under warmer conditions. Ask an installer to size the unit for your local water temperature and household demand rather than choosing by the largest GPM number alone.
Choose indoor or outdoor installation
Indoor units need an appropriate location and venting that meets the manufacturer’s instructions and local code. Outdoor units avoid placing the heater indoors but still need a suitable site and protection appropriate to the unit’s design. Some models can be converted between installation types only with a separate accessory kit. Check what is included before you select a location.
Verify gas, plumbing, power, and venting requirements
A gas tankless heater may need an adequately sized gas line, suitable plumbing connections, electrical power, and the correct venting or outdoor placement. For example, the Westinghouse description specifies 3/4-inch NPT plumbing connections and 120V AC power, while the FOGATTI description also calls for 120V AC. Have a qualified installer verify that your home’s existing connections can support the model you choose.
Check certification and safety features
Look for certification and safety details in the product information and installation manual. Several options here are described as CSA certified. Features such as freeze protection, flame-failure protection, and overheat protection differ by model, so confirm which protections the exact unit provides and how they work in your climate.
Review freeze protection and maintenance needs
Tankless systems still need care, especially where freezing temperatures are possible. Read the manufacturer’s directions for freeze protection, draining, and periods when the heater will be unused. Do not assume a built-in freeze feature covers every condition; the FOGATTI description, for example, gives specific guidance to drain the unit in severe cold or after extended non-use.
Compare warranty terms and listing details
Warranty lengths and coverage can differ between the full unit and the heat exchanger. Read the complete terms, including any conditions that apply to installation and maintenance. Also confirm current availability, included accessories, and exact model specifications on the product listing before ordering.
Frequently Asked Questions
Can a gas tankless water heater supply an entire house?
It can serve a whole home if it is sized for the household’s peak hot-water demand and installed correctly. The number of simultaneous showers and appliances, incoming water temperature, and heater capacity all affect performance.
Does a higher GPM rating always mean better performance?
No. The maximum GPM is only one factor. Colder incoming water requires a greater temperature rise, which can reduce the flow available at your chosen output temperature. Compare GPM and BTU ratings with your actual household needs.
Which model in this group has the highest listed flow rate?
The outdoor Westinghouse model is listed at up to 8.1 GPM. That maximum does not guarantee the same flow under every water-temperature or installation condition.
Do gas tankless water heaters need electricity?
Requirements vary by model. The Westinghouse and FOGATTI product descriptions specify a 120V AC connection. Check the exact unit’s installation instructions to confirm its electrical needs.
Can I install an indoor model outside?
Only if the manufacturer supports that configuration and you follow its requirements. The MIZUDO description says indoor or outdoor installation is possible with an accessory kit that must be purchased separately. Do not assume other indoor models can be converted.
Are tankless water heaters immune to freezing?
No. Some models include freeze protection, but cold-weather use and long periods of non-use may still require specific steps. Follow the manufacturer’s instructions for your model and installation conditions.
Should I install a gas tankless water heater myself?
Gas supply, venting, plumbing, electrical connections, and local code requirements make installation a job to plan carefully. A qualified professional can verify that your home’s gas line and installation location are suitable and help size the unit correctly.
Final Recommendation
For higher-capacity indoor use, the GASLAND Gasmart E stands out on listed BTU output and includes CSA certification and stated safety protections. If you want an outdoor model with the highest listed flow rate here, consider the Westinghouse. The MIZUDO is the app-control pick, while the FOGATTI offers a strong indoor capacity with specific operating guidance to keep in mind. Before choosing any model, match its output to your household’s peak demand and confirm installation requirements with a qualified professional.
