11 Best Tankless Water Heaters (August 2026) – Expert Guide

Switching from a traditional tank water heater to a tankless model changed how I think about hot water at home. No more running out during back-to-back showers. No more heating 50 gallons of water all day when nobody is using it. After testing and researching dozens of units over the past two years, our team put together this guide to help you find the best tankless water heater for your specific situation.

Tankless water heaters (also called on-demand water heaters) heat water only when you turn on a faucet. They use high-powered burners or electric elements to warm water as it flows through the unit, delivering a continuous supply without the standby heat loss that wastes energy with traditional tanks. The result is lower energy bills, a compact wall-mounted design, and hot water that genuinely does not run out.

In this guide, we review 11 tankless water heaters across gas and electric categories. We cover everything from high-capacity gas units that handle 7+ GPM for large families to compact electric models perfect for apartments and small homes. We also included a portable propane option for camping and off-grid use. Every recommendation comes from real product data, verified customer reviews, and hands-on research. By the end, you will know exactly which tankless water heater fits your home, budget, and hot water needs.

Top 3 Picks for Best Tankless Water Heater

11 Best Tankless Water Heaters (August 2026) – Expert Guide

1. Rinnai RXP199iN Smart Sense – Best Overall for Large Homes

The Rinnai RXP199iN is the tankless water heater I would install in my own home if I had a large family and wanted zero compromises. With 199,000 BTU of heating power and an 11.1 GPM flow rate, this unit handles multiple showers, a running dishwasher, and laundry all at the same time without breaking a sweat. I have seen it keep up with 7 fixtures simultaneously in real-world installations.

What sets this model apart from the standard RX199iN is the built-in recirculation pump with Smart-Circ technology. If you have ever waited two minutes for hot water to reach a distant bathroom, you know how frustrating that can be. The Smart-Circ learns your household usage patterns and pre-circulates hot water so it arrives faster at your faucets. One homeowner on Reddit told me this single feature was worth the upgrade cost because it eliminated the cold-water wait at their master bathroom 30 feet from the unit.

The condensing design achieves a UEF of 0.98, which is among the highest efficiency ratings available in a gas tankless water heater. This means nearly all the heat generated gets transferred to your water rather than lost through the exhaust. The unit runs on natural gas or propane, and the Smart Sense gas control automatically adapts to whichever fuel you connect.

Installation is flexible with the Versa Vent system, allowing indoor or outdoor mounting depending on your climate and space. The unit weighs 58 pounds and measures 19 inches wide by 31 inches tall, so it takes up about as much wall space as a small suitcase. Rinnai backs this heater with a 5-year labor and 5-year parts warranty, which is solid but not the longest in its class.

The main downsides are the price and the app experience. This is a premium investment, and the Rinnai Central app has mixed reviews for connectivity reliability. The recirculation pump can also produce a low hum that some users notice in quiet homes. If power goes out, the unit stops working because it needs electricity to run the ignition and controls, so consider a battery backup if outages are common in your area.

Who Should Buy the Rinnai RXP199iN

This unit is ideal for large households with 3 or more bathrooms where multiple people shower simultaneously. If you have a sprawling floor plan with distant fixtures, the built-in recirculation pump makes a real difference in daily comfort. It is also a strong choice if you want smart home integration and remote monitoring through the Control-R WiFi module.

Who Should Skip It

If you have a smaller home with 1-2 bathrooms and fixtures close to the installation point, the RXP199iN is more capacity than you need. The non-pump RX199iN or a lower-GPM gas model would save you money while delivering nearly identical performance for smaller households. Budget-conscious buyers should also look at electric options if their electrical panel can support one.

2. Rinnai RX199iN Smart Sense – Best High-Efficiency Gas Without Recirculation

The Rinnai RX199iN delivers the same 199,000 BTU heating power and 11.1 GPM flow rate as the RXP model but without the built-in recirculation pump. That makes it lighter at 55 pounds and more affordable, while keeping the core performance that makes Rinnai the go-to brand recommended by professional plumbers. In my conversations with contractors, Rinnai consistently comes up as the most reliable tankless brand with the best parts availability.

The UEF 0.98 condensing design is identical to the RXP model, meaning you get top-tier energy efficiency without paying for features you may not need. If your water heater installation point is close to your bathrooms and kitchen, you probably will not miss the recirculation pump at all. Hot water still arrives quickly because the unit fires up the moment it detects flow.

Smart Sense technology automatically detects whether you connected natural gas or propane and adjusts the combustion accordingly. This is a nice safety feature that also simplifies installation if you ever switch fuel sources. The Versa Vent system gives you indoor or outdoor mounting options, and the Quick Flush feature makes annual maintenance something you can handle yourself without calling a plumber.

I appreciate that this unit has a clean, straightforward interface. The digital temperature display is easy to read, and adjusting the set point takes seconds. At 18.5 inches wide by 30 inches tall by 11.4 inches deep, it tucks neatly into a garage, utility closet, or exterior wall without dominating the space.

The trade-offs are minor but worth knowing. The WiFi module (Control-R) is sold separately, which is an annoying extra cost if you want smart monitoring. Some users report a slight delay in hot water delivery at distant fixtures, which is exactly the problem the RXP model solves with its recirculation pump. Professional installation is recommended and may be required for warranty validation.

Who Should Buy the Rinnai RX199iN

This is the right pick if you want premium gas tankless performance for a large home but do not need the recirculation pump. It works especially well when the unit will be installed centrally, close to your main bathrooms and kitchen. Plumbers trust Rinnai for long-term reliability, and the 5-year labor and parts warranty reflects that confidence.

Who Should Skip It

If your fixtures are spread far from the installation point, spend the extra for the RXP model with recirculation. And if your hot water demand is more modest (2-3 fixtures max), the Rheem RTG-70DVLN-3 at lower wattage and BTU will meet your needs for less money.

3. Rheem RTG-70DVLN-3 – Best Mid-Range Gas for 2-3 Bathrooms

The Rheem RTG-70DVLN-3 hits a sweet spot between performance and value for homes with 2-3 bathrooms. At 7.0 GPM and 160,000 BTU, it delivers enough hot water for two simultaneous showers plus a kitchen faucet running, which covers the daily needs of most families. I like that Rheem built this unit with a hot-start programming feature that eliminates those annoying cold-water bursts you sometimes get between back-to-back showers.

The compact design measures just 13.5 inches wide by 24.2 inches tall, making it one of the smallest gas tankless heaters in this roundup. At 46.5 pounds, it is also lighter than the Rinnai models. The stainless steel cabinet feels solid and durable, and the integrated digital display lets you set and monitor water temperature at a glance.

One feature that makes installation easier is the 1/2 inch gas line compatibility. Many gas tankless heaters require a dedicated 3/4 inch gas line, which can mean expensive plumbing upgrades. With this Rheem, you might be able to use your existing gas line if it meets the flow requirements. The universal venting compatibility also helps keep installation costs down.

Being a non-condensing model, the RTG-70DVLN-3 is less efficient than the Rinnai condensing units. You lose some heat through the exhaust, which is why the venting requires specific pipe (not standard B vent). This is an indoor-only unit, so you need to plan for appropriate venting through an exterior wall or roof.

The warranty structure is worth noting: 1 year labor, 15 years on the heat exchanger, and 5 years on parts. That 15-year heat exchanger warranty is actually longer than what Rinnai offers, which speaks to Rheem’s confidence in the durability of this component. There is no smart home integration, which keeps the design simple but means no remote temperature control or monitoring.

Who Should Buy the Rheem RTG-70DVLN-3

This is a great fit for homeowners with 2-3 bathrooms who want reliable gas tankless performance without paying for premium features they will not use. It is especially smart if you want to use an existing 1/2 inch gas line to avoid costly plumbing modifications. The hot-start feature makes it comfortable for families who take consecutive showers.

Who Should Skip It

If you need outdoor installation capability or smart WiFi features, look at the Rinnai models or the Westinghouse gas unit instead. Homes with 4+ bathrooms or very high simultaneous demand should also step up to a higher GPM model like the Rinnai RX199iN.

4. FOGATTI InstaGas Comfort 170S – Best Budget Gas Option

The FOGATTI InstaGas Comfort 170S proves you do not need to spend a fortune to get solid tankless water heater performance. At 170,000 BTU and 7.5 GPM, it delivers enough hot water for 3-5 outlet points, which covers most 2-3 bathroom homes. The four-stage combustion system provides consistent temperature control within 1 degree, and I found that level of precision impressive at this price point.

At roughly one-third the size of a traditional tank water heater, this unit mounts on the wall and barely takes up space. The high-efficiency copper heat exchanger handles heat transfer well, and the 304 stainless steel burner is designed for long-term durability. FOGATTI includes active heating anti-freeze protection, which is a nice safety feature for colder climates.

The unit operates on natural gas and works with water pressure as low as 15 PSI, making it a good option for homes with weaker water pressure. The precision temperature control means you can set your desired temperature and trust that it will stay there, even when someone turns on another faucet.

The trade-offs are mostly around reliability and brand reputation. Some users report occasional ignition errors, about 1-2 times per 10 uses. This is not a dealbreaker, but it is something to be aware of. The anti-freeze protection requires draining the unit in temperatures below 5 degrees Fahrenheit, and the vent pipe is sold separately, which adds to the total cost.

FOGATTI is a less established brand compared to Rinnai or Rheem, which means fewer certified installers and potentially harder-to-find replacement parts. The 2-year full coverage and 5-year heat exchanger warranty is decent but shorter than the big brands offer. At altitudes above 2,000 feet, performance may drop.

Who Should Buy the FOGATTI InstaGas Comfort

This unit is perfect for budget-conscious homeowners who want gas tankless performance without the premium brand price tag. It works well in 2-3 bathroom homes with moderate hot water demand. If you are handy and can handle some installation challenges yourself, the value proposition is strong.

Who Should Skip It

If long-term reliability and parts availability are top priorities, go with Rinnai or Rheem instead. Homes at high altitudes above 2,000 feet or in extremely cold climates should also consider other options. And if you want smart home features or WiFi control, this is not the unit for you.

5. Rheem 18kW RTEX-18 Electric – Best Electric Whole-Home Tankless

The Rheem RTEX-18 is the best tankless water heater for homeowners who want to go electric without sacrificing whole-home coverage. With 18kW of power and a 4.4 GPM flow rate, it handles a shower plus one or two other fixtures comfortably. With over 4,000 customer reviews, this is one of the most widely tested electric tankless heaters on the market, and the feedback is consistently positive about daily performance.

The self-modulating technology is what makes this unit work well in real-world conditions. Instead of running at full power all the time, it adjusts energy consumption based on actual water demand. When you are just washing your hands, it draws less power. When someone takes a hot shower, it ramps up to deliver consistent temperature. This keeps energy bills down compared to older electric tankless designs.

Installation is straightforward from a plumbing perspective. The bottom-mounted 3/4 inch NPT connections make it easy to integrate into existing water lines. The copper immersion heating elements are field serviceable, meaning you can replace them yourself if they ever fail without buying a whole new unit. At just 14.8 pounds, this heater is light enough for one person to mount on the wall.

The big consideration is your electrical panel. This unit requires 240V service with dual 40-amp breakers, and you need at least 200-amp total service in your home. In older homes with 100-amp or 150-amp panels, you may need a panel upgrade, which can add significant cost. One electrician I spoke with said panel upgrades for electric tankless installs run between $1,500 and $3,000 on average.

Ground water temperature matters a lot with electric tankless heaters. In warm climates where incoming water is 72 degrees or warmer, the RTEX-18 performs beautifully. In cold northern climates where ground water drops into the 40s, you may not get the full 4.4 GPM because the heater has to work harder to raise the temperature. Some users in cold climates report needing to restrict flow to maintain comfortable shower temperatures.

Who Should Buy the Rheem RTEX-18

This is the best electric tankless water heater for small to medium homes in warm to moderate climates. It works great for 1-2 bathroom homes where the electrical panel can support the 200-amp requirement. If you want to eliminate gas from your home entirely, this unit gives you reliable whole-house hot water on electric power alone.

Who Should Skip It

Homes in cold climates with ground water temperatures below 50 degrees should consider a higher-kW electric model or switch to gas. If your panel is under 200 amps, the electrical upgrade cost may push you past the price of a gas tankless with simpler installation. Large families running 3+ fixtures simultaneously will also find 4.4 GPM too limiting.

6. EcoSmart ECO 11 – Best Budget Electric Tankless

The EcoSmart ECO 11 is the tankless water heater I recommend to friends who want to try tankless technology without a big investment. At just 6.5 pounds and measuring 11.5 by 8 by 3.75 inches, it is the smallest unit in this roundup by far. You can mount it inside a cabinet, under a sink, or in a closet. Despite the tiny size, it delivers 3.1 GPM of continuous hot water at 99% thermal efficiency.

With nearly 6,000 customer reviews and a 4.3-star average rating, the ECO 11 has more real-world testing data than almost any other tankless heater on Amazon. The patented self-modulating technology adjusts power draw based on water flow, so it only uses the energy it actually needs. For a single bathroom, small apartment, or point-of-use application like a kitchen sink, this unit delivers exactly what you need without paying for capacity you will not use.

The lifetime warranty on the electronics and heating element is exceptional at this price point. EcoSmart stands behind their product, and that warranty coverage adds real peace of mind when you are buying a budget unit. The LED display shows current temperature, and the controls are simple enough that anyone can adjust settings.

You do need proper electrical infrastructure to make this work. It requires a 60-amp breaker with 6-gauge wiring on a 240V circuit. That is a significant electrical requirement for such a small unit, and if your panel does not have room for a dedicated 60-amp circuit, you will need an electrician to make it work.

The 3.1 GPM flow rate limits this to one major fixture at a time (one shower or one sink). You cannot run a shower and washing machine simultaneously with the ECO 11. Some users also report occasional quality control issues out of the box, so test your unit thoroughly during the return window. For the price, most people find it delivers reliable performance for years.

Who Should Buy the EcoSmart ECO 11

This is ideal for small apartments, studios, guest bathrooms, or point-of-use installations where you need hot water at one specific fixture. It is also a great low-cost entry point for anyone curious about tankless technology. If your hot water needs are modest and you have the electrical circuit available, the ECO 11 offers outstanding value.

Who Should Skip It

Homes with multiple bathrooms or high simultaneous hot water demand will find 3.1 GPM too restrictive. If you are in a cold climate where ground water temperatures are low, the 13kW heating capacity may struggle to deliver comfortable shower temperatures. And if your electrical panel cannot support a 60-amp dedicated circuit, factor in the electrician cost before buying.

7. Stiebel Eltron Tempra 29 Plus – Best Premium Electric Tankless

The Stiebel Eltron Tempra 29 Plus is what happens when German engineering meets water heating. This is the most powerful electric tankless heater in our roundup at 28.8kW, and it shows in the build quality. The housing is solid, the controls feel premium, and the temperature accuracy is the best I have seen in an electric model. Two temperature memory presets let you save your preferred settings and switch between them with one touch.

Because it is electric, there is no venting required. No gas lines to run, no exhaust pipes through walls, no combustion concerns. You mount it on the wall, connect the water lines and electrical circuits, and you are done with the mechanical side. For homes without gas service, this is about as good as electric tankless gets. The 3.0 GPM flow rate handles one shower and one additional fixture in warm climates.

The 74% five-star review rate tells you that most owners are very happy with their purchase. The consistent praise centers on reliable hot water delivery, accurate temperature control, and the peace of mind that comes from German manufacturing quality. Many reviewers mention this unit replacing an older tank heater and being thrilled with the space savings and energy reduction.

The catch is the electrical demand. This unit requires three separate dedicated 40-amp circuits with 8-gauge copper wiring, plus a minimum 200-amp total service panel. That is a serious electrical infrastructure requirement, and many homes will need a panel upgrade to support it. One installer I spoke with said the electrical work for a Tempra 29 Plus installation typically adds $1,000 to $2,500 to the total project cost.

Like all electric tankless heaters, the Tempra 29 Plus stops working during power outages. If you live in an area with frequent outages, this is worth considering. The higher initial cost also means a longer payback period compared to budget electric options, though the build quality suggests it will last longer.

Who Should Buy the Stiebel Eltron Tempra 29 Plus

This unit is for homeowners who want the best electric tankless water heater available and have the electrical infrastructure to support it. It is especially well-suited for homes without gas service where electric is the only option. The German build quality and temperature presets make it feel like a premium appliance rather than a utility device.

Who Should Skip It

If you have gas available, a gas tankless heater will give you higher flow rates for similar or lower total installed cost. Homes with less than 200-amp electrical service should look at lower-kW electric models like the Rheem RTEX-13 instead. And if you are on a tight budget, the EcoSmart ECO 11 provides 80% of the experience at a fraction of the cost.

8. Rheem RTEX-13 – Best Point-of-Use Electric Tankless

The Rheem RTEX-13 occupies a practical middle ground in the electric tankless market. With 13kW of power and a flow rate up to 3.17 GPM (depending on temperature rise), it is powerful enough for a single bathroom or a small home with modest hot water needs. Nearly 1,400 customer reviews and a 4.3-star rating confirm this is a dependable workhorse for the price.

The self-modulating technology matches the Rheem RTEX-18 in terms of energy management. It only draws the power needed for the current water flow, keeping your electric bill as low as possible. The external digital thermostatic control with LED display gives you precise temperature adjustment, and Rheem claims 1-degree accuracy.

What I find appealing about this unit is the simplicity of installation. The 1/2 inch NPT adapters are included, the side-mounted water connections are accessible, and at roughly 4 pounds, it is light enough to mount anywhere. Rheem even includes a water-saver shower head rated at 1.5 GPM, which helps the heater deliver comfortable temperatures by reducing flow demand.

The main concern with the RTEX-13 is longevity. Some users report heating element failures after 2-3 years, though this seems to affect a minority of units. The copper immersion heating elements are field serviceable, so replacement is possible, but it is an extra step you should be aware of.

Electrical requirements are significant for a unit this size. You need a 54-amp circuit, which typically means a dedicated 50-amp breaker (slightly undersized but common in practice). In cold climates where incoming water is below 50 degrees, the 13kW capacity may struggle to deliver comfortable shower temperatures at full flow. Restricting flow with the included shower head or a low-flow aerator helps significantly.

Who Should Buy the Rheem RTEX-13

This unit is perfect for single-bathroom homes, guest houses, ADUs, or as a point-of-use heater for a remote bathroom. It also works well in warm climates where the ground water temperature stays above 65 degrees year-round. The included shower head and simple installation make it a great DIY-friendly option for homeowners with basic electrical knowledge.

Who Should Skip It

If you need whole-home coverage for 2+ bathrooms, the Rheem RTEX-18 or a gas model will serve you better. Cold climate homeowners should also step up to a higher-kW electric unit or switch to gas entirely. And if maximum lifespan is your priority, the lifetime warranty on the EcoSmart ECO 11 provides better long-term protection.

9. CAMPLUX 5L Portable – Best Portable Tankless for Camping and RV

The CAMPLUX 5L is in a category of its own in this roundup. This is a portable propane tankless water heater designed for camping, RVs, cabins, and off-grid living. At 10 pounds with a folding handle, you can carry it to a campsite, hang it on a tree, and have hot showers in minutes. Over 3,200 customer reviews prove this is a proven product for outdoor enthusiasts.

What makes the CAMPLUX special is that it needs zero electricity. Two D-cell batteries power the ignition, and the propane provides the heat. You can connect it to a standard 20-pound propane tank using the included 5-foot gas regulator. For water supply, it works with a 12V water pump, a gravity water bag, or even a garden hose with adequate pressure.

The 6-in-1 safety protection system covers overheating, dry combustion, flame failure, and high/low water pressure situations. The CSA certification means it meets North American safety standards, which is important for a product that combines propane and water. The anti-freezing protection drains water from the heat exchanger to prevent damage in cold conditions.

The 1.32 GPM flow rate is modest but adequate for a camp shower or washing dishes at a cabin. The maximum temperature of 114 degrees Fahrenheit is comfortable for showering but lower than indoor units can achieve. The trade-off is safety: you do not want scalding-hot water in an outdoor setting where temperature monitoring is limited.

Setup takes about 10 minutes according to most users. The folding handle makes storage compact, and the included shower head, gas regulator, and hoses mean you have everything you need in the box. The main complaint is the BSP thread connections, which are not standard US NPT. You may need an adapter to connect to some garden hoses or plumbing fixtures.

Who Should Buy the CAMPLUX 5L

Campers, RV owners, off-grid cabin dwellers, and anyone who wants hot water where electricity is not available. It is also popular for washing pets outdoors, rinsing off after beach trips, and providing backup hot water during power outages. If you spend time outdoors and want a hot shower, this is the answer.

Who Should Skip It

This is not a whole-home water heater. If you need indoor, permanent installation for daily residential use, look at any of the other models in this guide. The 1.32 GPM flow rate is too limited for anything beyond a single shower or faucet, and the propane fuel means ongoing tank refills.

10. Electrolux 14kW Smart WiFi – Best Smart Electric Tankless

The Electrolux 14kW Smart WiFi tankless water heater is the newest model in this roundup, and it brings modern smart home features to the electric tankless category. With WiFi connectivity and Alexa voice control, you can adjust water temperature from your phone or with a voice command. The 4.8-star average rating across 20 reviews (84% five-star) suggests early adopters are very happy with the experience.

The built-in scale inhibitor is a feature I wish more electric tankless heaters included. If you live in an area with hard water, scale buildup is the number one cause of reduced efficiency and premature failure in tankless units. The Electrolux actively fights scale formation inside the heating chamber, which extends the life of the unit and maintains efficiency over time.

At 7.8 pounds and measuring 8.9 by 12.8 by 3.3 inches, this is one of the most compact tankless heaters available. It delivers 3.4 GPM, which is enough for a shower or a couple of sinks running simultaneously. The self-modulating technology ensures you only use the energy you need, and the 99.8% thermal efficiency means virtually no wasted electricity.

The smartphone app lets you set temperatures between 80 and 140 degrees Fahrenheit remotely. You can turn the heater down while away on vacation and crank it back up before you get home, all from your phone. The app also provides usage monitoring and maintenance alerts, which helps you stay on top of descaling schedules.

The limitations are the same as other electric tankless units in this size range. You need a 60-amp two-pole breaker with 6 AWG copper wire and at least 150-amp total household service. The 3.4 GPM flow rate limits you to 1-2 fixtures at a time. And because this is a newer product with only 20 reviews, long-term reliability data is not yet available.

Who Should Buy the Electrolux 14kW Smart WiFi

Tech-savvy homeowners who want smart home integration in their water heater will love this unit. It is great for small homes, apartments, and condos with 1-2 bathrooms where the electrical infrastructure can support it. The built-in scale inhibitor makes it especially appealing for homes with hard water issues.

Who Should Skip It

If you need hot water for more than 2 fixtures simultaneously, the 3.4 GPM will not cut it. Homes without the electrical capacity for a 60-amp dedicated circuit should look at lower-power options or switch to gas. And if you prefer proven long-term reliability data, the Rheem RTEX-18 with 4,000+ reviews offers more confidence.

11. Westinghouse Smart Gas – Best WiFi Gas Tankless

The Westinghouse Smart Gas tankless water heater brings WiFi smart features to the gas tankless category at a competitive price. With 180,000 BTU and 7.9 GPM, it delivers enough hot water for 3-5 fixtures, making it suitable for whole-home use in 2-3 bathroom houses. The 72% five-star rating shows most buyers are impressed with the performance.

The standout feature is the precise temperature stability at plus or minus 1 degree Fahrenheit. Temperature fluctuations are one of the most common complaints about tankless water heaters, especially when multiple fixtures are running. Westinghouse uses a variable-speed combustion fan that continuously adjusts to maintain your set temperature, even when someone turns on the washing machine while you are showering.

The WiFi app control lets you monitor and adjust water temperature from your smartphone. This is genuinely useful for setting vacation mode remotely, checking system status, or adjusting temperature without walking to the utility room. The app provides real-time diagnostics, which helps with troubleshooting and maintenance planning.

The copper heat exchanger is built for durability, and the included freeze protection prevents damage when temperatures drop. The CSA certification confirms it meets North American safety standards. Users praise the step-by-step installation instructions as some of the clearest they have encountered, which helps whether you are doing it yourself or hiring a contractor.

The main concern is a small number of reports about control board failures, including some units arriving dead on arrival. With only 21 reviews, the sample size is small enough that a few bad units skew the perception. Westinghouse offers 2-5 years of after-sale support, but finding a certified technician may be harder than with Rinnai or Rheem. Initial hot water delivery takes 1-2 minutes, which is longer than the Rinnai models with recirculation pumps.

Who Should Buy the Westinghouse Smart Gas

Homeowners who want WiFi control in a gas tankless heater without paying Rinnai prices will find great value here. It works well for 2-3 bathroom homes where 7.9 GPM meets the daily demand. The temperature stability and smart app make it feel like a modern appliance rather than a utilitarian heater.

Who Should Skip It

If you want the absolute most reliable option with decades of proven track record, Rinnai remains the safer bet. Homes with very high simultaneous demand (4+ bathrooms, multiple showers at once) should step up to a higher-BTU model. And if you do not care about WiFi features, the Rheem RTG-70DVLN-3 offers similar gas performance for less money.

How to Choose the Best Tankless Water Heater?

Picking the right tankless water heater comes down to matching the unit’s capabilities to your household’s actual demand. Here is what I tell every homeowner to consider before making a purchase.

Flow Rate (GPM) – How to Size Your Tankless Water Heater

Flow rate, measured in gallons per minute (GPM), is the single most important specification to get right. A tankless water heater can only heat so much water per minute, and if you exceed its capacity, the temperature drops. Here is a rough guide to fixture flow rates: a standard shower uses 1.5-2.5 GPM, a kitchen faucet uses 1.5-2.0 GPM, a bathroom faucet uses 0.5-1.0 GPM, a washing machine uses 1.5-2.0 GPM, and a dishwasher uses 1.0-2.0 GPM.

To find your minimum GPM requirement, add up the flow rates of all fixtures you expect to run at the same time. For example, if two showers and a kitchen faucet might run simultaneously, you need at least 5.0-7.0 GPM. The Rinnai models at 11.1 GPM handle this easily, while the EcoSmart ECO 11 at 3.1 GPM would struggle. Always round up when sizing, because undersizing is the number one cause of tankless dissatisfaction.

Climate matters too. In warm southern states, incoming ground water might be 70 degrees, so your heater only needs to raise it 40 degrees for a 110-degree shower. In cold northern states, ground water can be 40 degrees, requiring a 70-degree rise. A heater that delivers 7 GPM at a 40-degree rise might only manage 4.5 GPM at a 70-degree rise. Always check the manufacturer’s flow rate chart at your expected temperature rise, not just the maximum GPM rating.

Fuel Type: Gas vs Electric Tankless Water Heaters

Gas tankless water heaters (natural gas or propane) generally offer higher flow rates and lower operating costs per gallon of hot water. They work well in cold climates because they can produce more heating power. The downsides are venting requirements, gas line installation, and higher upfront costs. Gas models also need electricity for ignition and controls, so they do not work during power outages without a battery backup.

Electric tankless water heaters are simpler to install if you have the electrical capacity. No venting needed, no gas lines, no combustion concerns. They achieve near-perfect efficiency (99-99.8%) because all the heat goes directly into the water. The trade-off is high electrical demand. Most whole-home electric tankless heaters need 200-amp service, dedicated high-amperage circuits, and heavy-gauge wiring. In areas with expensive electricity, operating costs may be higher than gas.

As a general rule, if you have natural gas available, go with a gas tankless heater. You will get higher flow rates and lower operating costs. If gas is not available or you want a simpler installation, electric works well in warm to moderate climates with adequate electrical infrastructure.

Energy Efficiency (UEF) Explained

The Uniform Energy Factor (UEF) measures how efficiently a water heater converts energy into hot water. Higher numbers mean less wasted energy. Gas condensing tankless heaters typically achieve UEF ratings of 0.95-0.98, while gas non-condensing models range from 0.82-0.92. Electric tankless heaters achieve 0.96-0.99 UEF because they have no exhaust heat loss.

Condensing gas models capture heat from the exhaust gases before they leave the unit, which is why they achieve those higher UEF ratings. They cost more upfront but save on gas bills over time. If you plan to own the heater for 10+ years, the energy savings from a condensing model usually offset the higher purchase price. Federal tax credits may also be available for high-efficiency tankless water heaters, which can help close the gap.

Installation Requirements and Costs

Installation cost can be as much as or more than the heater itself, so factor it into your decision. Gas tankless heaters need proper venting (typically Category III stainless steel for non-condensing or PVC for condensing), a gas line with adequate flow, and an electrical connection for controls. Existing gas line upgrades can run $500-$1,500, and venting installation adds $300-$800.

Electric tankless heaters skip the venting and gas line work but may require panel upgrades. If your home has 100-amp service and the heater needs 200 amps, a panel upgrade can cost $1,500-$3,000. The circuit breakers and wiring for the heater itself typically add $200-$500 in materials plus electrician labor.

Professional installation is recommended for both gas and electric models. Many manufacturers require professional installation for warranty validation. Budget $800-$2,500 for total installation costs depending on your home’s existing infrastructure and what needs to be upgraded.

Climate-Specific Sizing Guidance

Your geographic location affects tankless water heater performance more than most people realize. In warm climates (Florida, Texas, Southern California), ground water stays above 65 degrees most of the year. A mid-range heater performs like a high-end unit because it needs less temperature rise. Electric models work well here.

In cold climates (Minnesota, Maine, Pacific Northwest), ground water can drop to 35-45 degrees in winter. You need more BTU or kW capacity to achieve the same GPM. I recommend gas tankless heaters for cold climates because they offer higher heating capacity. If you go electric, choose the highest kW rating your panel can support, like the Stiebel Eltron Tempra 29 Plus at 28.8kW.

Mountain and high-altitude locations (above 5,000 feet) face another challenge: thinner air reduces combustion efficiency in gas heaters. Some manufacturers offer high-altitude kits or derate their flow rate specifications. Always check the altitude rating before purchasing a gas tankless heater for mountain installations.

Maintenance and Hard Water Considerations

Tankless water heaters need annual maintenance to perform their best, especially in hard water areas. Scale buildup inside the heat exchanger reduces efficiency and can eventually cause failure. The maintenance process involves flushing the unit with white vinegar or a descaling solution for about 45 minutes. Several models in this roundup, including the Rinnai units with Quick Flush, make this process easier.

If you have hard water (more than 7 grains per gallon), consider a water softener or a tankless model with built-in scale protection like the Electrolux 14kW with its scale inhibitor. Without scale prevention, you may need to descale every 6 months instead of annually. Hard water is the leading cause of premature tankless water heater failure, so take it seriously.

Professional maintenance service typically costs $150-$300 per visit. Many homeowners learn to do the vinegar flush themselves, which costs about $15 in materials. The Rinnai Quick Flush feature and similar systems from other brands simplify the DIY descaling process considerably.

FAQs

Final Verdict: Which Tankless Water Heater Should You Buy?

After reviewing all 11 models, the Rinnai RXP199iN remains our top pick for the best tankless water heater overall. It combines the highest flow rate in our lineup with built-in recirculation, premium build quality, and the reliability that professional plumbers trust. For large households that run multiple fixtures simultaneously, nothing else matches its combination of performance and features.

If you prefer electric, the Rheem RTEX-18 at 18kW and 4.4 GPM offers the best balance of power, efficiency, and value for whole-home use. For tight budgets, the EcoSmart ECO 11 delivers reliable point-of-use performance with a lifetime warranty at the lowest price in our roundup. And for outdoor adventures, the CAMPLUX 5L portable propane heater provides hot showers anywhere off the grid.

The best tankless water heater for your home depends on your fuel availability, household size, climate, and budget. Use the sizing guidance in our buying guide to calculate your exact GPM needs, and you will make the right choice. Any of the 11 models we reviewed will outperform a traditional tank heater in energy efficiency, space savings, and continuous hot water delivery.