Best Tankless Water Heaters [A-Z Guide]

A tankless water heater might be a great idea for your home. They can cut your water heating bill, last longer than a traditional tank and take up less room. ENERGY STAR says its certified gas tankless models save a family of four about $95 a year on gas compared with a standard gas storage heater, and puts tankless life expectancy at 20 years.

What is a Tankless Water Heater?

Most people are used to water tanks, which can hold a large capacity of water, and usually use gas to heat that water all at once so that the home has hot water for sinks, dishwashers, baths, showers, and washing machines.

A tankless water heater does the same thing, except without the tank. Instead of heating all of the water and working to keep it hot, the tankless water heater heats water as it goes through the heater. It keeps no water in reserve, but the better systems will heat enough water fast enough that you will always have plenty of hot water for your needs.

What are the Advantages of a Tankless Water Heater?

Tankless water heaters have lots of advantages over water tanks, including:

• They can use less energy than a tank: the U.S. Department of Energy estimates about 33% savings for a gas tankless heater, and real savings vary with how much hot water you use
• They save money on your energy bill
• They take up less space, and some can even be installed outside
• They heat water on demand, so they do not run out as long as you stay within the unit’s flow rate
• They can last up to twice as long as a water tank heater

What are the Drawbacks of Tankless Water Heaters?

While they might seem like a perfect choice, given all of their advantages, there are a few disadvantages to consider before you make a decision, including:

• Tankless water heaters can be significantly more expensive
• They may also be more expensive to install – especially if you are replacing a water tank
• They may have a lower water output, so your shower may be a little chilly if you are also doing laundry
• Cheaper or smaller tankless water heaters may not be best for very cold climates

A better unit can handle several tasks at once, but every tankless heater has a limit: the colder your incoming water, the less hot water per minute it can deliver, so the flow rating (GPM) alone is not enough. Rinnai’s spec sheet says maximum flow rates vary with the temperature setting and the temperature rise.

What tankless water heater is best for me?

There are a few basic types of tankless water heaters, including indoor and outdoor, propane, natural gas, and electric heating, and different sizes – specifically in reference to how much water, in GPM (gallons per minute), they can heat.

There is also what is called a “point of use” tankless water heater, which is a small, and small output, unit designed not for the whole house but for a single location – like to heat only shower water.

Our reviews and recommendations come from our own experience, the experiences and feedback of our friends and colleagues, and the reviews and experiences of actual verified customers.

After these reviews, we will give some advice on how to choose a tankless water heater that is best for your home and your needs. 

Once you have done that, match your result to the picks below.

Best Large Propane: Rinnai RX180iN Smart Sense Tankless Water Heater

Rinnai is a company that shows up on our various buyer’s guides more than almost any other. While their products are not the least expensive, Rinnai is a strong choice for a gas tankless heater.

We used to list the outdoor RU199eP here; Amazon no longer carries it. Its replacement in this slot is the Rinnai RX180iN, and it is a simpler buy: its Smart Sense gas control runs on either propane or natural gas, and its Versa Vent lets it be installed indoors or outdoors, so one model covers the cases that used to need four.

It is a whole-house condensing unit rated at 180,000 BTU and up to 10 gallons a minute at Rinnai’s maximum rating, and less when the incoming water is cold, which is enough for many large families.

Rinnai lists a Uniform Energy Factor of 0.98, a Quick Flush feature that simplifies the yearly flush, and the Rinnai Central app for setup and service. The residential warranty is 15 years on the heat exchanger and 5 years on parts and labor, if you register it within 90 days of installation (otherwise labor drops to 1 year).

Rinnai recommends professional installation and points buyers to its Find a Rinnai PRO page; we would not install a gas tankless heater ourselves either.

Best Large Natural Gas Tankless Water Heater: Rinnai RU199iN Natural Gas Tankless Water Heater

For the second unit in our list of best tankless water heaters, we are right back with Rinnai, one of the finest and most innovative companies we have ever encountered.

This time we are looking at the Rinnai RU199iN large output natural gas tankless water heater, the indoor model from the same RU199 line as the outdoor unit we used to list here (Amazon no longer carries the outdoor RU199eN).

It is a whole house tankless water heater, with plenty of output for even larger homes: up to 11 gallons a minute at Rinnai’s maximum rating, which Rinnai says can serve up to 7 fixtures at once, and the same 199,000 BTU heating power.

With specs like these, this Rinnai tankless water heater is built for large homes, large families and lots of activities. It is an indoor unit, so it needs venting, which is one more reason to have it installed by a professional.

It comes with Circ-Logic for pairing with an external recirculation pump, which keeps hot water moving so distant taps get hot water sooner, and Wi-Fi monitoring is available with Rinnai’s Controlr module (sold separately).

The Rinnai RU199iN is a condensing, ENERGY STAR qualified unit; Rinnai’s product page for the RU199 series lists a Uniform Energy Factor of 0.93 to 0.95. The residential warranty is 15 years on the heat exchanger, 5 on labor and 1 on parts.

Rinnai recommends professional installation and points buyers to its Find a Rinnai PRO page; we would not install a gas tankless heater ourselves either.

Best Large Electric Tankless Water Heater: Stiebel Eltron Tempra 29 Plus Electric Tankless Water Heater

An electric water heater with enough heating and water flow for larger houses and larger families is a more difficult proposition than a propane or natural gas-powered unit, but the over-engineered Stiebel Tempra 29 Plus is built for the job. It replaces the Tempra 36 Plus we used to list, which Amazon no longer carries.

While it does not have the extremely high volume of hot water offered by the propane and natural gas heaters above, at 28,800 watts it is the most powerful Tempra sold on Amazon, and Stiebel’s Advanced Flow Control trims the flow slightly rather than letting the water go cold when demand jumps.

It has two temperature memory presets, needs no venting, and is engineered and manufactured in Germany, with a level of quality in materials and construction rarely found in any modern appliance.

Any tankless water heater will probably need installation by a licensed professional. Electric whole-house tankless water heaters all need a 240-volt electrical supply with a lot of capacity: Stiebel’s listing calls for three separate 40-amp breakers with 8-gauge copper wiring and a minimum 200-amp service to the house (28,800 watts at 240 volts is 120 amps), so many homes need a service upgrade. Have a licensed electrician check your panel before you buy.

Best Medium Propane Tankless Water Heater: Rinnai RE160iP Propane Tankless Water Heater

At the risk of sounding like a broken record, in our buyer’s guide and review of best tankless water heaters on the market today we go again to Rinnai for both our Propane and Natural Gas tankless water heaters for medium to small homes.

We used to list the RL75IP here. Rinnai retired the RL line in 2022 and replaced it with the RE series, so the pick is now the Rinnai RE160iP, a non-condensing indoor propane unit rated at 160,000 BTU and up to 6.6 gallons a minute at Rinnai’s maximum rating, less when the incoming water is cold.

Meant for indoor installation, it is the size of a small suitcase, heats only when a tap runs, and has an LED screen on the front. Wi-Fi control needs Rinnai’s Controlr module, sold separately. Being non-condensing, it is less efficient than Rinnai’s condensing models such as the RU199 and RX180, but it should still use less energy than a typical tank heater.

The residential warranty is 15 years on the heat exchanger, 5 on labor and 1 on parts. Rinnai recommends professional installation and points buyers to its Find a Rinnai PRO page; we would not install a gas tankless heater ourselves either.

Best Medium Natural Gas Tankless Heater: Rinnai RE180iN Natural Gas Tankless Water Heater

As mentioned just above, Rinnai is our strong choice for both our Propane and Natural Gas tankless water heaters for medium to small homes, not to mention large homes and families: 4 recommendations out of 7 in this guide.

The Rinnai RE180iN is the model Rinnai’s own transition guide names as the replacement for the RL75 we used to list here. It is a non-condensing indoor natural gas unit rated at 180,000 BTU and up to 8.5 gallons a minute at Rinnai’s maximum rating, less when the incoming water is cold.

Meant for indoor installation, it is the size of a small suitcase, heats only when a tap runs, and has an LED screen on the front. Wi-Fi control needs Rinnai’s Controlr module, sold separately. Being non-condensing, it is less efficient than the RU199iN above, but it should still use less energy than a typical tank heater.

The residential warranty is 15 years on the heat exchanger, 5 on labor and 1 on parts. Rinnai recommends professional installation and points buyers to its Find a Rinnai PRO page; we would not install a gas tankless heater ourselves either.

Best Medium Electric Tankless Heater: Rheem RTEX-24 Electric Tankless Water Heater

It seems pretty simple to us. Even in this smaller range, a tankless water heater is a major investment and something you will have in your home, use and depend on for many, many years. 

As such, we see great wisdom in sticking with the most respected companies in the industry, established leaders in product quality, innovation and performance. This is why Rheem, along with Rinnai and Stiebel Eltron, is such a frequent recommendation in Home Caprice’s buyer’s guides and reviews and is represented in our list of the best tankless water heaters.

And for small to medium-sized homes, smaller families and milder climates, the Rheem RTEX electric tankless water heater is an obvious recommendation.

The Rheem RTEX-24 has the most advanced water modulation system on the market and will deliver consistently hot water even with rapidly changing demands. This system, along with an advanced digital thermostat, superior heating elements and many other factors make for a heater that, like other electric resistance heaters, turns almost all the electricity it uses into heat.

The RTEX24 is rated for up to about 6 gallons a minute of hot water and a temperature rise of up to 65 degrees Fahrenheit, but not both at once: at a 65 degree rise a 24 kW heater delivers only about 2.5 gallons a minute (24,000 watts x 3.412 ÷ 500 ÷ 65). Check the flow chart for your incoming water temperature.

Meant for inside installation, this Rheem tankless electric water heater is quite small – 18 by 19 inches and only 4 inches deep. Do not treat it as a DIY project: whole-house tankless electric heaters need 240-volt power on their own heavy circuits, so have a licensed electrician do the wiring.

There are few, if any, electric heaters that can match this one, in terms of performance and specifications, and even less that can offer the energy efficiency, the reliability and material quality, or the outstanding reputation that the RTEX24, or any Rheem product, has.

And, at its surprisingly low price, the Rheem RTEX-24 Electric Tankless Water Heater offers an almost unbelievable value and is an easy choice for Best medium electric tankless water heater.

Features & Specifications

• Tankless Electric Water Heater
• Maximum Temperature Increase: 65 Degrees Fahrenheit
• Flow Rate: Up To 6 Gallons a Minute
• All Copper Immersion Chamber with Brass Fittings
• Digital Temperature Display and Thermostat
• Advanced Water Modulation System
• Warranty: 5 Years

Best Point of Use Tankless Water Heater: EcoSmart ECO 11 Electric Tankless Water Heater

If you don’t want to provide hot water for your whole house, but just in a single place – a shower, a sink or a washing machine, for example – a Point of Use tankless water heater is a perfect choice.

And the best one we’ve found is the EcoSmart ECO-11, a well-built unit that is simple to use, with digital temperature control, precise energy management features and a limited lifetime warranty. Like other electric tankless heaters it runs on 240 volts, so have a licensed electrician install it; EcoSmart’s manual calls for a qualified electrician and a qualified plumber.

With a much lower water flow than any of the whole-house tankless water heaters above, the EcoSmart ECO11 can heat up to 2 gallons of water a minute, which is plenty for one or two sinks, a shower or other single-use applications. In a warm climate that may cover a bathroom, but with cold incoming water plan on a single sink or a trickle of shower.

By allowing your larger water heater to work less, and just heating water as you need it, the ECO 11 can save you on utility bills, depending on how much hot water you use. And, with its patented Self-Modulating technology, this EcoSmart point of use tankless water heater turns almost all the electricity it uses into heat, like other electric resistance heaters.

A simple, high-quality unit that offers great performance and exceptional energy efficiency, and should offer many years of trouble-free service, the EcoSmart ECO 11 Electric Tankless Water Heater is our choice for the best point of use tankless water heater.

Features & Specifications

• Tankless Electric Point of Use Water Heater
• Flow Rate: Up To 2 Gallons a Minute
• Digital Temperature Display and Thermostat
• Patented Self-Modulation Technology
• Warranty: Limited Lifetime

How do I Choose the Right Tankless Water Heater?

If you are building a house, planning a major renovation, replacing a broken water tank heater or just want to save on your heating bills, you probably have already decided on a tankless water heater.

But which tankless water heater?

The brand and model are easy to narrow down: the choices above come from established makers. The harder part is sizing.

All you have to do is decide how much hot water you need, then match it to the picks above.

How Much Hot Water Do I Need?

This is determined with a simple GPM (gallons per minute) calculation, using the following guidelines:

• A sink faucet will use around .5 GPM of hot water.
• A dishwasher will use around 1.0 GPM of hot water.
• A clothes washer will use around 2.0 GPM of hot water.
• A shower will use around 2.5 GPM of hot water.
• A bathtub will use around 4.0 GPM of hot water to fill (but, of course, you can fill it more slowly).

If you have an idea of how many of these items you may be using at the same time – that is, will more than one person be taking a shower at once, or will you have the shower, clothes washer, and dishwasher running simultaneously – then you can get an idea of the maximum GPM of hot water your new tankless water heater should provide. These flow rates are rough typical figures, so check the ratings on your own fixtures. Then check the temperature rise, because a heater delivers less flow the colder the incoming water is. Rinnai’s spec sheet says maximum flow rates vary with the temperature setting and the temperature rise, and electric units are affected most: a 24 kW electric heater raising water by 65°F delivers only about 2.5 gallons a minute.

• Our large tankless water heaters provide 7.5 to 11 GPM of hot water.
• Our medium tankless water heaters provide 6 to 7.5 GPM of hot water (the ranges overlap at 7.5 because the large electric pick tops out there).

Regardless of your use, you probably don’t want less than 6 GPM for a whole-house tankless water heater.

Another way of figuring this out is based on the size of your family and your home.

• If you have a large house (2,500 square feet or larger), regardless of family size and use, you probably want a large tankless water heater.
• If your house is smaller than 2500 square feet, you are fine with a medium-sized heater.
• If you have 4 or more people in your family, excluding infants, you probably want a large tankless water heater – even in a smaller house.
• If you have 3 or fewer people, and a smaller house, again you should be fine with a medium-sized tankless water heater.

Whatever you determine, it is good to remember that – while you never want to spend more money than necessary – you can’t go wrong getting a little more capacity than you need. So if you are unsure (or if you have children who are approaching their teens!) you might want to get a larger unit – it might even save you money in the long run.

Along those lines, our affiliate links go to Amazon, where prices change often, but you might also notice that, for many of our recommendations, the Amazon page also has links leading to different-sized models of the same unit – offering more or less GPM of hot water.

The different models in the same line – especially with industry-leading brands like Rinnai, Stiebel Eltron, Rheem or EcoSmart, will always be great choices and can be purchased with just as much confidence, and ultimately will provide just as much satisfaction, as our primary recommendations.

We hope that this buyer’s guide has been a great help in your selection process and that you will turn to us again in the future!