Over time your home appliances begin to break down and need to be replaced, and water heaters are no exception. Conventional water heaters used to be the standard go-to – they provided literally a hot tank of water for your showering and laundering needs. But as technology advances, so do our appliances.
Tankless water heaters take up far less room and provide instant, endless hot water. In this article we share the best tankless water heaters on the market today.
Tankless Water Heaters Explained
When we think of water heaters, it’s pretty easy to visualize the large tank that is constantly heating 20-80 gallons of water so that it’s ready when we need it.
And if you share a home with many others, you also know the feeling of the hot water “running out.”
Tankless water heaters take both the visual of a conventional water heater and the feeling of one away. 'Tankless' are small appliances that are wall-mounted and about the size of a circuit box. They don’t have the capacity to hold heated water, but they work with electricity or gas to very quickly heat water when you need it. For this reason, they are also called “on demand” water heaters.
There are many advantages of tankless hot water systems that we touch on in this article. The top four benefits include:
- 1Tankless water heaters are a space saving appliance.
- 2They can provide an endless amount on hot water.
- 3They will help you reduce energy waste. Most tankless water heaters will help reduce your water heating costs by 10-15% according to Green Riverside.
- 4The expected lifespan for a tankless water heater is 20+ years – nearly double the expectancy of a conventional model!
Types of On Demand Hot Water Systems
Gas tankless water heaters (using either natural gas or propane) are about twice the size of electric tankless water heaters. The size difference is to accommodate the unit’s pilot light system. These units also require ventilation to the outdoors to safeguard your home from carbon monoxide.
Many people who enjoy using gas to heat their home furnace find a lot of the same value in using a gas tankless water heater, but because they are more complicated to install and do require additional venting, they are often more costly than electric units to buy and set up but from then on in they become cheaper to run.
Electric tankless water heaters are about half the size of their gas-powered counterparts. They have a very small footprint, as you can see in this pictures of a garage installation.
They don’t require any ventilation to the outdoors and are often cheaper and easier to install.
According to Eemax, “Electric tankless water heaters can achieve a thermal efficiency rating of 99 percent, meaning that 99 percent of the electricity that goes into the warming process comes out as heat.”
When purchasing tankless hot water heaters for your home you will have the option to buy a whole house tankless water heater or several dual units to cover the different areas of your home (bathrooms, kitchen, laundry etc.) The number one factor in making this decision will be deciding if you need to use any of these areas simultaneously.
Because tankless water heaters heat the water as they go, two or more areas using water will reduce the flow rate at which the water comes out.
RV Tankless Units
Smaller on-demand hot water systems for RVs or other areas with smaller water needs are called “point-of-use” tankless heaters. They are generally installed directly under the sink or shower where you would like to have hot water.
Many of these units are so small that nobody will know they are there, and because they are installed so close to the water flow the heat will literally be instantaneous. In this YouTube video, RV users Jared and Kris share their experience with a tankless point-of-use system.
Ultimate Guide in Choosing the Best Tankless Water Heating System
Household Size (Usage)
The size of your home will help determine what size and style of tankless water heater is best suited for your needs. An even better indicator than size though, is how often you will be using hot water and at how many points.
A large home using only one shower at a time will need a smaller system than the same large home that uses several showers simultaneously.
Indoor or Outdoor
Many tankless water heaters have the capacity to be installed either outdoors or indoors, and this is often decided on how the unit fits into your plumbing the best. For homes that are replacing a conventional water heater, it makes most sense to install their new tankless system in the same location.
Outdoor tankless heaters are made to stand up to the elements of both rain and sun, and even freezing temperatures in most cases. These units often have freeze protection and small internal heaters to keep their parts running smoothly.
The danger in this instance is a power outage, which might have the capacity to freeze your unit and cause permanent damage. If you plan to use an outdoor tankless heater during freezing weather, it would be pertinent to have a back-up generator to run it in case of an outage.
The fuel type that you choose for your tankless water heater will be much up to your preference. Electric units are about half the size of their gas-powered sibling units and they do not require any additional ventilation to the outdoors.
Gas-powered units do require ventilation and will need to be hooked up to either natural gas or propane. Many of the differences between electric and gas tankless water heaters are charted here at the Go Tankless website.
Temperature Range (BTU)
The general temperature range for all tankless hot water heaters is about 80F to 140F.
Some commercial models will go slightly hotter than this for sanitation purposes.
For gas-powered units only, you will also see a BTU indicator.
BTU stands for British Thermal Units. Each BTU is the quantity of heat that is needed to make one pound of water increase by one-degree Fahrenheit.
The larger the BTUs, the more heating power – but in general the average shower temperature is 105F, so you can feel confident that your hot water heater will provide the temperature that you need.
Flow Rate (GPM)
GPM simply stands for Gallons Per Minute, and this is the output that you can expect when using your tankless water heater. Usually the GPM listed indicates the maximum flow output. If you are running more than one shower or sink simultaneously, this flow rate will be slightly decreased because the areas are sharing hot water.
Energy Efficiency & Certification
Tankless water heaters can be up to 99% energy efficient, and about 24%-34% more energy efficient than traditional water heaters. If you install several tankless water heaters in your home instead of one, this can also make the system more energy efficient.
In terms of certification, even though electric and gas-powered models are both great energy savers, only gas-powered tankless water heaters have the capability to be certified with Energy Star. We go into the reasoning behind this further on in our article.
Installation & Maintenance
For the best outcome, we at Plumbing Lab always recommend that you have a professional install your new tankless water heater. For electric tankless heaters, this is a pretty straightforward process and can be done easily in about an hour’s time.
For gas tankless heaters the proper ventilation will need to be built-in as well to ensure that you don’t have carbon monoxide coming into your home. The same applies also to maintenance.
Electric tankless heaters are maintenance free – we just recommend that you check the filter several times a year to make sure there isn’t any debris blocking your water. Gas-powered tankless heaters require an annual inspection to ensure proper gas flow and upkeep.
Lifespan & Warranty (Durability)
Tankless water heaters are built to last for 20+ years, almost twice as long or more than their conventional counterparts. Therefore, many models come with an extended warranty. When reviewing your warranty, it’s important to understand exactly what is covered and what will be your own responsibility.
Some of the units we look at cover everything from parts to labor, whereas other warranties only cover defective products.
8 Best Tankless Water Heaters Reviewed
1. Stiebel Eltron 24 Tempra Plus
Best Overall Tankless Water Heater
Flow Rate (GPM)
86F – 140F
16.6 x 4.6 x 14.5
ANSI/UL Std. 499
We at Plumbinglab have already rated the Stiebel Eltron 24 Tempra Plus the best whole house electric tankless water heater on the market, as you can see in this article. Today we’re going to take that one step further and declare the Stiebel Eltron the best overall tankless water heater.
This system has proved itself time and time again to provide an excellent choice for your hot water needs, from an outstanding company that truly stands behind their product.
Our review focuses on the 24 Tempra Plus model, but the Stiebel Eltron comes in many different sizes. You’ll want to base your decision on these three factors: the size of your home, the ground temperature where your home is, and your hot water needs.
This helpful chart will help you see the difference between the models. Where I live the groundwater is 62F, so the Tempra 24 Plus provides (on average) enough hot water for two showers and one sink to run simultaneously at 3.8 gallons per minute.
This flow rate is only slightly less than the Stiebel Eltron’s max flow rate of 4.68 gallons, and the decrease will save you from having a “cold water surprise,” as the manufacturers share in this YouTube video. This is called “Advanced Flow Control” and it was invented and specific to the Stiebel Eltron brand.
One of the most impressive things about the Stiebel Eltron Tempra 24 Plus is that it is German-made and comes with a 7-year warranty for leakage and a 3-year warranty for parts.
Unlike a lot of the appliances in American homes that “just aren’t built like they used to be” you can count on the Stiebel Eltron to last.
2. Rinnai RUC98iN Ultra Series
Best Tankless Gas Water Heater
Flow Rate (GPM)
199,000 BTUs /
98F – 140F
18.5 x 10 x 26
Energy Star Certified
When it comes to tankless water heaters, you can rest assured that the Rinnai company knows what they are talking about. This company is top of the range in my opinion, so if you want quality then Rinnai is for you.
While most of the world would probably still believe that tankless water heaters are a more “modern” appliance, the Rinnai company actually first launched their first tankless water heater in 1921!
With nearly 100 years of experience under their belt, the Rinnai company sets high standards for their products.
The best tankless gas water heater is the Rinnai RUC98iN Ultra Series. This model hooks up to the natural gas supply in your home and uses two heat exchangers to provide hot water to your entire home at an unprecedented rate of up to 9.8 gallons per minute.
The unit is Energy Star Certified and has an estimated cost of $172 to run annually, which is about a quarter of the cost of propane tankless water heaters.
On the Lowe’s website, user JohnInCharlotte8741 calls the Rinnai RUC98iN a good investment, and states,
"Already saving a lot on our gas bill. Hot water quick and for as long as you like, regardless of how many teenagers are in the house taking 3 showers a day!"
Because the Rinnai RUC98iN runs on natural gas, the installation will be a bit more involved than that of an electric version, primarily because it requires venting to the outside.
Make sure that you have a professional do the installation to avoid and voided warranties, because Rinnai offers 12 years on the heat exchanger, 5 years on parts and even 1 year on labor which is almost unheard of.
This is a great choice for those wanting a whole house water system. Paying more upfront will get you quality and efficiency over the years.
3. Eccotemp L10
Best Tankless Water Heater for RV
Flow Rate (GPM)
74,500 BTUs /
50F – 140F
13.6 x 8 x 25.5
The Eccotemp L10 is what is known as a “recreational water heater.” It is not a permanent solution for a water heater and it can be installed outdoors only.
That being said, the Eccotemp L10 is the perfect solution for having a hot shower while camping, giving your dogs a heated bath, or installing a shower on the outside of your pool house or RV.
So how does it work? Using a standard 20 lb propane tank that you would use for a grill and a garden hose, the Eccotemp L10 creates hot water at up to 2.7 gallons per minute. The setup is easy and you won’t need professional help, and the unit is easily stored when not in use.
It really is the best outdoor gas tankless water heater for portable RV hook-up that we could find – fast, convenient and easy to maintain.
On the Eccotemp website, one reviewer said that,
"The L10 seems to be a perfect fit for our off-the- grid cabin. Fed by a 250-gallon roof top rainwater collection tank and a small battery-operated pump, the L10 fired as soon as it saw water and sustained the hot water nicely. I would definitely recommend this unit."
Anyone feeling a little weary of this DIY hot-water set-up can rest assured that Eccotemp wants you to have the safest experience possible. There are several built-in safety features, including an automatic 20-minute shut-off timer and a 45-degree tilt switch that will also turn the unit off.
4. Camp Chef HWD5 Triton
Best Portable Tankless Water Heater
Flow Rate (GPM)
34,000 BTUs /
38 F – 102F
12 x 4 x 15
For the best portable tankless water heater, or “shower on-the-go” as I call it, look no further than the Camp Chef HWD5. This portable water heater is middle-of-the-road as far as portable tankless heaters go, but it is portable, affordable and easy to set-up and use. It even comes with its own shower head that has four settings: off, mist, shower and jet.
Unlike the water pressure that you’re probably accustomed to indoors, the Camp Chef has a max flow of 1.5 gallons per minute. For an extra hot shower, the flow will be more like 0.5 gallons per minute. This is standard for such a portable device, but may take a little getting used to.
I recommend the Camp Chef for those camping, in campers or for light or quick use. This is the smallest and lightest tankless portable option on our list.
Customer Denise remarks, "I love my portable hot water heater. I run a bed-and- bath. All my guests come here and love my beautiful outdoor shower. Everybody wants to know where I got that hot water heater. The water is the hottest water ever, and the pressure is unbelievable. Just love it."
5. Takagi T-K4-OS-NG
Best Outdoor Gas Tankless Water Heater
Flow Rate (GPM)
13.8 x 8.5 x 20.3
If you’re interested in the idea of a gas tankless hot water heater for your home, but you’re not thrilled with the idea of installing additional ventilation, then the Takagi T-K4-OS-NG is a suitable option for you.
This Takagi model is designed to be installed on the outside of your home and has a built-in power venting system, meaning no ventilation is required to be built into your home.
The product description states that the hot water heater can easily run three showers in warmer climate and two showers in cooler climate, but many reviewers have remarked that the Takagi goes above and beyond that..
If, however, you’re replacing an indoor tankless water heater or you just don’t want a unit that will be outside and open to the elements, Takagi has a very similar model gas tankless water heater than can be installed indoors. You can find that product here on Amazon, the TakagiT-KJr2-IN-NG.
The two units run almost completely the same, but the outdoor unit provides a little bit of a faster water flow and does not require the ventilation. Both products are top-notch and suitable for anyone wanting reliable hot water.
6. Ecosmart ECO 36
Best Whole House Electric Tankless Water Heater
Flow Rate (GPM)
21 x 3.625 x 17
Watersense, UL-499, ETL Listed
The Ecosmart ECO 36 is the most powerful EcoSmart tankless water heater that they make, and the company is so confident about its ability to provide hot water to your entire home that they even recommend it to those living in the Northern United States where the groundwater is much colder throughout the year.
We reviewed one of the smaller EcoSmart models (ECO 11) here as the best electric point-of-use system. This review focuses on the EcoSmart ECO 36 being the best whole house electric tankless water heater.
One very important thing to note with the ECO 36 is that it is so powerful that it will require a dedicated 150-amp breaker for itself. Unless you’ve had a similar product before, you will probably have to have an electrician install this to get you up-and-running (which could cost a few hundred dollars).
That being said, once the unit is installed, you’ll be glad you made the investment.
The ECO 36 is described as having the most advanced, self-modulating technology available. This means that it will adjust energy usage based on your needs, and you will see savings almost immediately.
Other reviews on the ECO 36 speak for themselves, as it is the most reviewed tankless water heater out there. This YouTube video by Jennifer goes extremely in depth with the product so that you can see whether or not it is the right tankless water heater for you.
7. Sio Green IR30 POU
Best Small Electric Tankless Water System
Flow Rate (GPM)
80F – 112F
8.5 x 3 x 13.5
Small tankless water heaters often get a bad reputation for breaking down after only a couple years, but most of the time it is because we’ve neglected to flush them out and maintain them properly (user error).
It makes sense – we have one sink we want to heat, we install and small point-of-use system for convenience, and we go about our time. Maintenance is not something you’ll need to worry about with the Sio Green IR30 POU Electric Tankless Water Heater.
This unit uses infrared heating elements. They state, “Our tankless hot water electric heater will create heat without direct contact with metals, which will, in turn, prevent corrosion, limescale deposit and calcium build-up. As a result, you will have to spend $0 on maintenance, no replacement parts, no filter required.”
As I mentioned above, the Sio Green is a small system electric tankless water heater.
It is made for a “handwashing station” and therefore should not considered powerful enough to run a shower or washing machine.
It is also made specifically for the southern United States, where the groundwater is above 62F, as you can see in their sizing guide below.
EBay user deanh9316 loves her Sio Green IR30! She claims,
"The Best! An excellent heater for a bath sink. Works as advertised and is very easy to install and adjust."
The only caveats worth mentioning on this Sio Green unit are the stipulations with their warranty. The IR30 does come with a two-year warranty, but the company doesn’t make it immediately clear that you must 1) register the product with the company within 30 days of purchase, and 2) have the unit installed professionally to have any claim on the warranty whatsoever.
8. Rheem RTGH-95DVLN
Best Indoor Direct Vent Tankless Water Heater
Flow Rate (GPM)
199,000 BTUs /
Up to 140F
18.5 x 9.75 x 27.5
One of the nice things about the Rheem brand is that they are well known in the United States, with certified technicians easily and readily available. Simply type in your zip code on their website to be connected with a Rheem specialist that can help you with your product, whether you’re installing it yourself or have questions.
Unlike some of the other gas models we’ve reviewed, the Rheem RTGH-95DVLN is a super high efficiency model, which means that it doesn’t require as thermal of ventilation and can even be vented using PVC pipe.
Everyone in your home will be able to use hot water at the same time, because this Rheem model can supply up to 9.5 gallons of hot water per minute. The unit has built-in digital controls that will tell you when it is due for maintenance, and even comes with a digital remote control.
Our full guide to Rheem water heaters can be found here.
Hot Water Needs
Conventional water heaters usually provide hot water for an entire house. When purchasing a tankless water heater, you have the option to purchase a whole house unit or several units to cover the different areas of your home.
The decision will depend on how much hot water you would like to use at one time. For instance, if several people will be showering at the same time, you would want to install several smaller units to maximize water flow.
Small System (camping, RVs, cabins)
Small tankless water heater systems are great for areas where you will only need hot water at one or two points, such as the shower and sink of an RV, or the sink and dishwasher of a small cabin.
As discussed above, you can also replace a whole house hot water heater with several of these small systems that work individually to provide you with the hot water that you need.
Point of Use
Point-of-use tankless water heaters are typically meant for one location only and are generally installed directly at the location of use. These very small water heaters are often used to heat water at a specific sink, or another area where you wouldn’t necessarily have a hot water connection, like an outdoor workshop or pool house.
Gas vs. Electric Units
Gas and electric tankless water heaters are both great options, but they do have their differences. While both options are smaller than conventional water heaters, a gas tankless heater is usually about twice the size as an electric tankless heater. This size difference is to accommodate the pilot/ignition.
Gas also needs to be ventilated to the outdoors, and electric units do not. For this reason, gas units are more expensive and require annual maintenance to make sure that the gas lines are clear and running smoothly. Both gas and electric units will provide endless hot water.
In the event of a power outage, your gas tankless heater will still provide hot water, whereas your electric heater will not. As stated in the reviews, gas will be cheaper as you run them and lower your energy bills when compared to electric units.
Selecting the Right Size
To choose the right size tankless water heater, you will need to consider the size of your home, the location and temperature of the groundwater, and how many water appliances that you would like to run simultaneously. Many of the brands we look at have handy calculators to help you determine the right size, like this one from Rinnai.
For a more visual approach to figuring out your sizing needs, this YouTube video by Supply House is very helpful.
Ignition and Venting
There are basically three different ways in which a tankless water heater will ignite. Most electric tankless water heaters have a direct spark ignition.
This means that they are ignited through electricity only when you turn on the hot water, and they do not have a standing pilot light. These models are considered very safe and do not need to be vented to the outdoors.
A pilot ignition is what most conventional water heaters have, and this is literally a small flame that constantly runs to heat your water when you’re ready. Tankless gas heaters also have this pilot light to ignite their fuel source (either natural gas or propane). It is mandatory that these units be installed with ventilation to the outdoors.
Battery ignitions are usually seen on portable tankless water heaters. These units usually require either 12V or D batteries and are paired with outdoor only models that you would hook-up to a standard grilling gas tank. Battery ignitions are a great source of hot water for camping or boating purposes.
All of the models of tankless water heaters that we reviewed in this article are really fantastic, but there are a few brands that really stand out above the rest.
In Europe, the Stiebel Eltron brand is a household appliance name that everyone knows, and its popularity is definitely growing in the United States as well. The company has been around for over 90 years and manufacturers their products with the highest of standards (built like a tank) in Germany.
Their company statement is “We have always engineered and manufactured our products as though our friends and neighbors were our customers. Our engineering and manufacturing excellence creates energy efficient products fulfilling the highest expectations of performance and reliability. We don’t cut corners.
We craft superior products. Our philosophy is to make it right, then keep making it better. There’s a reason everybody says we are... Simply the Best.”
The Rinnai brand was started in Japan over 100 years ago, and still uses a company philosophy based on Japanese tradition, focusing on harmony, spirit and truth. In 2018 they opened a manufacturing plant in the United States in Georgia. Rinnai is a highly trustworthy brand with over 30 million tankless water heaters installed worldwide.
Ecosmart is a company that aims to create cost and energy saving tankless water heaters and make them available to everyone. The company states that “EcoSmart’s main focus is the area of water heating.
It’s our goal to save the consumer money since energy consumed to heat water can account for up to 25% of the average energy bill due to outdated methods such as tank storage.”
Installing Tankless Hot Water Heaters
When installing a tankless water heater, the first objective will be to decide where to install it. If you’re replacing a conventional water heater, you’ll likely want to use the same location because the plumbing (and venting, if you have a gas unit) is already in place.
For newer homes, you might consider installing the water heater outdoors for even more space-saving function. For a general overview of what takes place, consider watching this YouTube video from This Old House.
Although installing a tankless water heater can be done with a lot of research and patience, we as well as most manufacturers suggest that you have a licensed professional do the installation as it is a big undertaking.
This Home Depot Project Guide suggests that only people with advanced knowledge in plumbing and electricity even attempt self-installation. Because of its difficult nature, most company’s will also void the warranty if you attempt to DIY.
Cleaning and Maintenance
All tankless water heaters, both electric and gas-powered need to be flushed out every once in a while. Most manufacturers recommend flushing your tankless water heater every 12-18 months. The process uses white vinegar to descale the boiler of your tankless water heater to wash out any built-up calcium deposits.
This helpful YouTube video by Matt Risinger walks you through the step-by-step process of flushing your tankless water heater.
In addition to flushing, gas-powered tankless water heaters need to be inspected annually to make sure that the gas lines are clear and working properly. This can be done by a licensed plumber, and is better to have done before you start having problems.
Certifications & Warranties
When it comes to home appliances in the United States, consumers often automatically look for the big yellow sticker that shares the Energy Star Certification information stating how energy efficient the product is compared to others and average yearly cost to operate.
For tankless water heaters, this way of comparing different tankless water heaters can be tricky because only gas-powered tankless water heaters have the capacity to carry the Energy Star rating. Why? In no way are we insinuating that electric tankless models are inferior or not energy efficient.
It’s simply because Energy Star does not have the category of electric tankless water heaters – yet. This article from Eemax further explains why the absence of the rating in this case isn’t a big deal.
There are a few other certifications that many tankless water heaters have, and most of these are in regards to the unit’s environmental impact, like the WaterSense Certification.
According to the Environmental Protection Agency (EPA), “The WaterSense label makes it simple to find water-efficient products, new homes, and programs that meet EPA’s criteria for efficiency and performance.
WaterSense-labeled products and services are certified to use at least 20 percent less water, save energy, and perform as well as or better than regular models.”
Warranties are another important issue to understand when purchasing your tankless water heater. When it comes to warranties, we recommend keeping a paper trail of all of your transactions regarding the appliance: from purchase to installation and any professional maintenance you have done on it.
Keeping records will help you to ensure that you have not voided the warranty. It’s also important to make note of what your warranty covers. Some warranties will include the replacement of the entire unit while others may only cover parts or defunct items.
Frequently Asked Questions
How many amps do these systems use?
The average whole house water heater uses about 120 amps. Depending on what other appliances you’ll be using simultaneously, many homeowners choose to upgrade their electrical systems to handle the heavier load when installing a tankless water heater.
How reliable are gas powered tankless water heaters?
Gas-powered tankless water heaters are incredibly reliable, and will continue you offer you hot water even in the event of a power outage. Although their upfront cost is quite costly, most users find that they pay for themselves in a matter of a few years.
How do I know which gas type water heater best fits my hot water needs?
The choice between natural gas and propane will be mostly a personal choice, but if your home is already hooked up to a natural gas line, we would suggest installing it there. Natural gas is less expensive and more readily available.
What type of maintenance is needed to ensure water heater longevity?
We recommend flushing your tankless hot water heater at least once every 12-18 months using a white vinegar solution to remove any calcium build-up. Installing a whole-house water filtration system can also help with this process. For gas-powered models, inspect your unit regularly to make sure that the gas lines are clear to avoid any combustion.
How much does it cost for a plumber to install an electric tankless hot water system?
The average installation cost for an electric tankless hot water system is between $800 and $1,500. You can receive a free estimate from this widget at the Home Depot website.
What are the differences between tankless & tank hot water heaters?
Tankless water heaters don’t have a readily available tank of hot water waiting to be used like conventional water heaters. Instead, they heat water very quickly as you need it (hence their nickname on-demand water heaters). For this reason, tankless hot water heaters can keep running for as long as you need hot water, whereas as soon as the water in the tank of a conventional heater is gone, it will need time to heat up the water again.
Whether you’re building a new home or updating your old conventional water heater, it’s clear that the future is in tankless water heaters. We have reviewed and support many models and brands, but our overall favorite tankless water heater is the Stiebel Eltron 24 Tempra Plus. We hope that this article has assisted you in your research!
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