Once you decide to ditch the tank, you face a mountain of options. Navigating flow rates, venting requirements, and fuel types gets confusing fast.
We created this guide to cut through the noise. We break down the pros and cons, explain exactly what to look for, and review the best tankless gas water heaters on the market right now.
- Concentric venting system
- Temperature lock
- Ideal for small to medium homes
- Self-diagnostic system
- 94% energy efficient
- Overheat film wrap
- Child locking technology
- LED screen and touch control display
- Stainless-steel vent kit
- Battery-powered ignition
- Weighs 23.8 pounds
- Flame failure protection
- Low emissions of nitrogen oxide
- Extra large water & gas inlets
- Natural gas or propane powered
Types of Tankless Gas Water Heaters
You generally have two categories to choose from: indoor and outdoor units. One of the biggest perks of going tankless is versatility; you can install them in places a traditional tank would never fit.
Old-school storage tanks usually live in the basement or garage. This forces hot water to travel a long way to reach your shower, which wastes water and time. Tankless gas models are compact enough to mount in a closet, a pantry, or even under a sink.
Indoor Tankless Gas Water Heaters
Installers mount indoor systems just like regular storage units, minus the bulky tank. You typically place these on a wall in a spot with good ventilation capabilities.
If you live in a region where winter brings freezing temperatures, an indoor system is your safest bet. Keeping the unit inside the heated envelope of your home prevents ice from destroying the internal components.
These heaters create condensation while they work. You need to ensure you have proper drainage set up to handle this moisture safely.
Pros
- Saves floor space: Indoor tankless heaters are small and wall-mounted, which frees up valuable square footage.
- Weather protection: Since the unit sits inside, it avoids exposure to rain, snow, and freezing winds.
- Lower risk of damage: Proper indoor installation minimizes the wear and tear caused by fluctuating outdoor conditions.
Cons
- Ventilation is mandatory: You must install specific venting pipes to move exhaust gases outside safely.
Outdoor Tankless Gas Water Heaters
Homeowners often choose outdoor units when retrofitting a house where adding new ventilation is too difficult or expensive. You simply mount the unit on an exterior wall.
If you plan to replace an old storage tank with a tankless unit, an outdoor model often requires less construction work. You won’t need to cut new holes in your roof or walls for exhaust vents.
Pros
- Simplified installation: You do not need to install complex indoor venting systems, which saves money and labor.
- Easier drainage: Outdoor units still need drainage, but you don’t have to worry about routing lines through interior walls.
- Safety factor: Keeping the combustion process outside reduces the risk of carbon monoxide or water leaks inside your living space.
Cons
- Weather vulnerability: These units are exposed to the elements; they are not suitable for areas with deep freezes unless they have specific freeze-protection kits.
- Lag time: If the unit is mounted far from your bathroom, you might wait a minute for hot water to traverse the distance.
What to Consider When Buying a Tankless Gas Water Heater
Finding the right unit depends on your specific home setup. Keep these factors in mind:
- Energy Factor (EF): Check the label for the Energy Factor rating. A higher EF number indicates a more efficient unit, which translates directly to lower monthly utility bills.
- Fuel type: You need to choose between natural gas and propane. Propane often burns cleaner and hotter, making it an efficient choice if you have a tank available (1).
- Physical dimensions: Measure your wall space before buying. While tankless units are smaller than tanks, gas models require extra room for exhaust piping and air intake compared to electric versions.
- Gallons Per Minute (GPM): This number tells you how much hot water the unit delivers at once. A small home might need 2 to 5 GPM, while a house with multiple bathrooms often requires 8 GPM or higher.
- Venting requirements: Most gas units require Category III stainless steel venting to handle acidic condensation. This is a specific cost you must factor into your budget (2).
Did You Know?
Product Reviews
We analyzed the market to find the most reliable, efficient, and user-friendly models. Here are our top tankless gas water heater reviews.
Rinnai V75IN 7.5 GPM Indoor Tankless Gas Water Heater
Best Tankless Gas Water Heater for Indoors
Energy efficiency is the name of the game for modern homes. This tankless gas water heater from Rinnai helps you lower your carbon footprint without sacrificing comfort.
A standout feature here is the concentric venting system. It keeps the unit safe and sealed, so you do not have to worry about exhaust fumes leaking into your home. This design makes it a top contender for indoor installation.
This boiler uses roughly 40% less energy than a traditional tank heater. Rinnai packed it with technology that locks in heat and stabilizes water temperature. With an energy factor of 0.82, it is a solid choice for the eco-conscious buyer.
It works best as a whole-house solution for small to medium-sized properties. The durable heating coils are efficient enough to handle a shower and a dishwasher running at the same time.
What We Like
Concentric Venting System
Safety is the main reason we like this boiler for indoor use. Rinnai utilizes a concentric venting design (4).
This system uses a single pipe with two channels: an inner tube for expelling exhaust and an outer tube for pulling in fresh air. It simplifies installation because you only need one penetration through your wall or roof.
This creates a sealed combustion system. No indoor air is used for burning gas, and no harmful fumes escape into your living space.
Temperature Lock
To prevent energy waste, this unit features a temperature lock. This ensures that accidental bumps or curious kids cannot drastically change the output temperature.
It heats water up to 160 degrees Fahrenheit and activates with a low flow rate of just 0.4 gallons per minute.
Ideal for Medium Homes
This unit comes from the Rinnai Value Series. While the brand is famous for massive commercial boilers, they designed this specifically for standard residential use.
Buying a massive heater for a small home results in wasted energy. This model hits the sweet spot, providing enough GPM for simultaneous appliance use without being overkill.
What We Don't Like
Slight Delay in Delivery
While powerful, this unit isn’t instant. Users report waiting up to 60 seconds for hot water to reach the tap, depending on how far the faucet is from the heater.
Product Specs
| Measurements | 23 inches by 14 inches by 9 inches |
| Weight | 45.6 pounds |
| BTU | 180,000 BTU |
| Gas type | Natural gas |
| Flow rate | 7.5 gallons per minute |
Our Ratings
Rheem RTGH-95DVLN GPM Tankless Gas Water Heater
Best Tankless Gas Water Heater for Cold Climates
If you live in the north, you need a boiler that doesn’t quit when the snow falls. This tankless gas water heater from Rheem is built specifically for harsh environments.
It features robust freeze protection that keeps the internal components safe down to -30 degrees Fahrenheit. You won’t have to worry about burst pipes inside the unit during a polar vortex.
We also appreciate the self-diagnostic system. It displays maintenance codes on a digital remote, letting you know exactly what is wrong before you call a plumber. It even alerts you when it is time for routine maintenance.
Designed for indoor use, it utilizes a two-pipe PVC direct vent system. It is highly efficient and includes an overheat film wrap for added safety.
What We Like
Serious Freeze Protection
Cold climates are tough on plumbing, but this Rheem unit fights back. The manufacturer utilizes ceramic heaters to protect the body and copper coating to preserve the pipes.
These materials allow the unit to survive temperatures as low as -30 degrees Fahrenheit. While it is technically durable enough for outdoor install in some zones, Rheem recommends keeping it indoors to maximize efficiency.
Smart Diagnostics
Troubleshooting is easier thanks to the built-in diagnostic software. If the heater acts up, the included digital remote displays a specific error code. This saves you time guessing what the problem is.
You can mount the remote anywhere convenient, making it simple to monitor temperatures and adjust settings without going into the utility room.
High Efficiency Rating
Rheem is known for efficiency, and this model boasts a 94% energy efficiency rating.
The stainless steel condensing heat exchanger captures more heat from the fuel, meaning you burn less gas to get hot water. With a max flow rate of 9.5 GPM, it can easily supply three bathrooms at once.
Overheat Film Wrap
Safety is paramount with gas appliances. This feature prevents the unit from reaching dangerous temperatures.
If you have high demands and need to link multiple units together, this film wrap allows for safe side-by-side clearance. It drastically minimizes fire hazards and overheating risks.
What We Don't Like
Audible Operation
It is not the quietest model on the block. Some homeowners notice a distinct sound when the burner ignites, though most do not find it intrusive.
Installation Complexity
The unit does not come with everything you need in the box. You may need specific pipe fittings and extra valves that are sold separately. Check the manual carefully before heading to the hardware store to avoid multiple trips.
Product Specs
| Measurements | 27.5 inches by 18.5 inches by 9.75 inches |
| Weight | 89 pounds |
| BTU | 199,000 BTU |
| Gas type | Natural gas |
| Flow rate | 9.5 gallons per minute |
Our Ratings
Eccotemp i12-LP Water Heater, 4 GPM
Best Tankless Gas Water Heater for the Eco-Minded Family
The Eccotemp i12 is a fantastic choice for a small apartment, a vacation cabin, or a tiny home. It is designed for households that only need hot water for one or two applications at a time.
It breaks the mold of boring white appliances with a sleek, tempered black glass front panel. The LED display shows your output temperature and current flow rate clearly.
We really like the child locking technology. Touch screens are magnets for kids, and this feature keeps your settings safe.
The box includes a horizontal stainless-steel vent kit, which saves you money on extra parts. It comes with a standard 110-volt power cord for easy plug-and-play power.
What We Like
Modern Aesthetic
Most water heaters are eyesores you want to hide. The Eccotemp i12 is different. The black glass panel looks modern and high-tech, which is great if the unit has to be installed in a visible area like a kitchen or utility mudroom.
Intuitive Touch Controls
The interface is simple. You get clear buttons for power and locking, plus arrows to adjust the temperature.
The central LED screen is bright and easy to read. It displays the water temperature and the GPM flow rate in real-time, so you know exactly how the unit is performing.
Vent Kit Included
Sourcing the right venting pipes is often a headache. Eccotemp includes a stainless steel vent kit in the box. Stainless steel is crucial because exhaust gases are corrosive and can eat through cheaper materials.
The kit is designed for horizontal termination, making wall installation straightforward.
Child Lock Feature
If you have children, you know they push every button they see. The child lock prevents accidental changes to the water temperature.
You simply hold the lock button for a few seconds to secure the interface. This prevents scalding accidents or surprise cold showers.
What We Don't Like
Sensitive to Maintenance
This unit requires careful handling during cleaning. Some users reported leaks after performing standard vinegar descaling flushes. Maintenance is key, so follow the manual’s instructions precisely to avoid damaging internal seals.
Odd Exhaust Size
The included exhaust pipe is a specific size that can be hard to match if you need to extend it. Make sure the included length works for your wall thickness before starting the installation.
Product Specs
| Measurements | 13.75 inches by 25 inches by 5 inches |
| Weight | 25 pounds |
| BTU | 25,000 to 80,000 BTU |
| Gas type | Liquid propane |
| Flow rate | 4 gallons per minute |
Our Ratings
Camplux 10L Outdoor Portable Propane Tankless Water Heater
Best Tankless Gas Water Heater for Outdoor Living
If you love camping, boating, or washing pets in the driveway, this Camplux unit is a game-changer. It is a true portable water heater designed for life off the grid.
The ignition is powered by two “D” cell batteries, so you do not need an electrical outlet to get hot water. You can take it deep into the woods as long as you have a propane tank and a water hose.
Safety features include a flame failure device, dry combustion protection, and anti-freeze technology. Despite its capacity, it is lightweight enough to mount on a dolly or hang on a fence post.
It delivers a respectable 2.64 GPM, which is plenty for a decent outdoor shower.
What We Like
True Off-Grid Capability
Camplux specializes in portability. This heater is perfect for cabins, horse stables, or RV trips. Since the ignition runs on batteries, you aren’t tethered to a generator or power pole.
It comes with a showerhead and hose attachment, making it an instant outdoor bathroom. Just connect water and gas, and you are ready to scrub down.
Seasonal Modes
The “Eco” and “Full” switch helps you manage fuel consumption.
Switch to Eco mode in the summer when inlet water is already warm. This lowers gas usage and prevents the water from getting dangerously hot. Use Full mode in the winter to ensure you get a comfortable temperature rise.
Vital Safety Sensors
Portable doesn’t mean unsafe. It includes dry combustion protection to stop the burner if there is no water, and a flame failure device that cuts the gas if the wind blows the fire out.
These features prevent gas leaks and ensure long-term durability.
Portable Yet Powerful
It measures about 20 inches high and weighs around 24 pounds. It is substantial enough to feel durable but light enough to pack in the trunk. It is a great balance between capacity and mobility.
What We Don't Like
Can Run Very Hot
The burner is powerful. On the “Full” setting, the water can get scalding hot if the flow rate is low. Always test the water with your hand before stepping under the spray.
Product Specs
| Measurements | 20.28 inches by 12.8 inches by 5.5 inches |
| Weight | 23.8 pounds |
| BTU | 68,000 BTU |
| Gas type | Propane gas |
| Flow rate | 2.64 gallons per minute |
Our Ratings
Rinnai RUR98iN Indoor Natural Gas Water Heater
Best Energy Efficient Tankless Gas Water Heater
The Rinnai RUR98iN is a powerhouse of efficiency. It uses condensing technology to achieve 95% thermal efficiency, meaning almost every dollar you spend on gas actually goes into heating your water.
This indoor unit features ultra-low nitrogen oxide emissions, meeting strict air quality standards in California and Texas. You can vent it using either concentric piping or standard PVC.
A unique feature is the oversized gas and water inlets. This design allows for higher flow rates without straining the system. In warm months, it can easily supply hot water to three bathrooms simultaneously.
It has a massive BTU range, scaling from 15,200 all the way up to 199,000 depending on demand.
What We Like
Eco-Friendly Performance
This unit is designed to be clean. The condensing system recaptures heat from exhaust gases to preheat incoming water. This boosts efficiency to 0.95 EF.
It is fully compliant with strict emissions standards, making it safe for indoor installation and better for the environment.
Flexible Venting
Rinnai gives you options here. You can use concentric venting (one pipe) or a twin-pipe PVC system. PVC is often cheaper and easier to source, which can lower your installation costs significantly.
High Flow Design
The larger inlet connections allow for serious volume. With a max flow rate of 9.8 GPM, this unit is built for large families. You can run the shower, the washing machine, and the kitchen sink at the same time without a drop in pressure or temperature.
Fuel Versatility
While this specific model number is for natural gas, Rinnai offers propane versions of the same engine. Propane is often a cheaper, cleaner alternative if you do not have a natural gas line hookup.
What We Don't Like
Professional Installation Recommended
This is a complex, high-performance machine. The plumbing and venting requirements are strict. We highly recommend hiring a licensed professional to install it to ensure the warranty remains valid.
Product Specs
| Measurements | 26 inches by 18.5 inches by 10 inches |
| Weight | 61.7 pounds |
| BTU | 15,200 to 199,000 BTU |
| Gas type | Propane or natural gas |
| Flow rate | 9.8 gallons per minute |
Our Ratings
| Product | Award | Dimensions | Weight (lbs) | BTU | Gas type | Flow rate (GPM) |
|---|---|---|---|---|---|---|
| Rinnai V75IN 7.5 | For Indoors | 23″ x 14″ x 9″ | 45.6 | 180,000 | Natural gas | 7.5 |
| Rheem RTGH-95DVLN | For Cold Climates | 27.5″ x18.5″ x 9.75″ | 89 | 199,000 | Natural gas | 9.5 |
| Eccotemp i12-LP | For The Eco-Minded | 13.75″ x 25″ x 5″ | 25 | 25,000 – 80,000 | Liquid propane | 4 |
| Camplux 10L | For Outdoor Living | 20.28″ x 12.8″ x 5.5″ | 23.8 | 68,000 | Propane gas | 2.64 |
| Rinnai RUR98iN | For Energy Efficiency | 26″ x 18.5″ x 10″ | 61.7 | 15,200 – 199,000 | Propane/natural gas | 9.8 |
FAQs
What are the downsides of a tankless water heater?
The main downsides are the initial cost and the potential for “cold water sandwiches.” Tankless units cost more to buy and install than traditional tanks. Also, if you draw hot water faster than the unit can heat it (like running three showers at once), the temperature may drop.
What size tankless water heater do I need?
Size depends on your groundwater temperature and peak usage. In warm climates, a 5 GPM unit might handle a whole house. In colder northern climates, you likely need 8 to 10 GPM to run multiple fixtures because the heater has to work harder to warm the freezing incoming water.
How long do tankless water heaters last?
You can expect a well-maintained tankless gas water heater to last 20 years or more. This is significantly longer than traditional storage tank heaters, which typically fail around the 10 to 12-year mark due to corrosion.
Are tankless gas water heaters worth the money?
Yes, they are generally worth the investment. While the upfront cost is higher, the long-term energy savings, endless hot water supply, and longer lifespan (20+ years) usually offset the initial price tag over time.
Which brand of tankless heater is the most reliable?
Rinnai, Rheem, and Navien are widely considered the top tier for reliability. Rinnai is particularly famous for durability, while Rheem offers excellent availability of parts and service technicians across the country.
How often do I need to flush my tankless heater?
You should flush your unit with a vinegar solution at least once a year to remove mineral scale buildup. If you have very hard water and no softener, you might need to do this every six months to maintain efficiency.
Do I need a separate heater for every bathroom?
No, a single high-capacity “whole house” tankless unit is usually sufficient. However, in very large homes where bathrooms are far apart, some homeowners install two smaller units to reduce the time it takes for hot water to arrive at the faucet.
Do I need to upgrade my gas line for a tankless heater?
Yes, often you do. Tankless heaters require a massive burst of energy to heat water instantly, often requiring 150,000 to 199,000 BTUs. A standard 1/2-inch gas line might not deliver enough fuel, so upgrading to a 3/4-inch line is a common requirement during installation.
