If you have decided to buy a new tankless water heater, this is the buying guide you are looking for. In case you are still hesitating whether you should go for a storage tank water heater or a tankless one, read our Storage Tank VS Tankless Water Heaters comparison article.

The Purpose of This Buying Guide

We made this comprehensive tankless water heater buying guide to help those wanting to get to know all the necessary information in order to buy the model that fits their needs the best. Why need a buying guide? There is a handful of well-known manufacturers making many different models with different specs which makes it hard to find the ideal one if you are no expert. We firmly believe that this is the only guide you will need to read in the topic and based on this you can make the right choice. Let’s jump in!

Best Gas Tankless Water Heaters

In the below table you can see our best gas tankless water heater picks based on different criteria.



  • GPM (inlet 52F, outlet 105F)

  • Outdoor only

  • Natural gas or propane-powered

  • Heat exchanger warranty: 12 years



  • GPM (inlet 52F, outlet 105F)

  • Indoor only

  • Natural gas-powered

  • Heat exchanger warranty: 12 years



  • GPM (inlet 52F, outlet 105F)

  • Indoor only

  • Natural gas or propane-powered

  • Heat exchanger warranty: 12 years



  • GPM (inlet 52F, outlet 105F)

  • Outdoor only

  • Propane-powered

  • Heat exchanger warranty: ?

Best Outdoor – Rinnai V-Series


Rinnai V series front side

Pros: Available in both natural gas and propane version. Even the least powerful V65 models have a pretty good GPM. Normally, enough for a household of 3-4 people in a not too cold area. Well built, lasting design.

Cons: A special condending vent kit is required which is not included in the product’s price. This elevates the costs even higher. 

Amazon Buyers’ Favorite Indoor – Noritz NRC66DVNG

Noritz NRC66DVNG front side

Pros: 12 year heat exchanger warranty. One of the most liked tankless water heater by actual buyers. It is a condensing heater: doesn’t require expensive stainless steel venting and hot exhaust. Cheaper PVC venting is enough. It is also more efficient than non-condensing water heaters.

Cons: Just like most condensing tankless water heaters, it is also quite expensive.

Best High-End Indoor – Rinnai RU-Series

Pros: Really powerful, high GPM. Liquid propane and natural gas versions available. Built-in recirculation pump. Stainless steel inside.

Cons: Powerful model of a reputable brand: high price, around 2,000 dollars. Vent to be purchased upon that.

Best Portable – Camplux 5L 1.32 GPM

Camplux 5L front side photo

Pros: Compact size. Portable. Can be operated outdoors. Mostly loved by buyers.

Cons: Low cost and portability comes at a cost: pretty low GPM. Although it does a great job at what it was supposed to be used for.



There are two things you need to consider price-wise when buying any water heater: the product price and the installation costs.

The product price for whole-house units is usually somewhere between 400 and 1,000 dollars. If you go for a premium brand it will be closer to or over 1,000 dollars.

In some cases the installation costs exceed the of the unit itself. There are two main scenarios:

  • Same vent can be used: 500 – 900 dollars
  • New vent needs to be installed: 800 – 1,400 dollars


Best Electric Tankless Water Heaters



  • GPM (inlet 52F, outlet 105F)

  • 6 KWs

  • 240 Volts

  • Warranty: 1 year



  • GPM (inlet 52F, outlet 105F)

  • 36 KWs

  • 240 Volts

  • Warranty: 7/3 years



  • GPM (inlet 52F, outlet 105F)

  • 36 KWs

  • 240 Volts

  • Warranty: 5 years limited



  • GPM (inlet 52F, outlet 105F)

  • 36 KWs

  • 240 Volts

  • Warranty: Limited lifetime



  • GPM (inlet 52F, outlet 105F)

  • 13 KWs

  • 240 Volts

  • Limited lifetime



  • GPM (inlet 52F, outlet 105F)

  • 24 KWs

  • 240 Volts

  • Warranty: 7/3 years

Best Point-of-Use – EcoSmart POU 6

Ecosmart POU 6

Pros: Perfect “under the sink” solution. Really good efficiency. Can be used as a booster. Can be connected to 208 and 240 Volts, too.

Cons: Only 1 year warranty. Will not work for a shower. Its price-to-performance ratio is not the best.

Best High-End Whole House #1 – Stiebel Eltron Tempra 36 Plus


Stiebel Eltron Tankless Heater – Tempra 36 Plus

Pros: 7 years and 3 years parts complete warranty. One of the few genuinely whole house electric models. 

Cons: Premium comes at a price – it is one of the more expensive models, normally closer to 1,000 dollars then 500 dollars. Minimum recommended household electric service is 300 A. 

Best High-End Whole House #2 – Rheem RTEX-36


Rheem 240V 4 Heating Chambers RTEX-36

Pros: A real electric whole house unit which is pretty rare. Really good GPM for an electric heater.

Cons: Just like the Stiebel Eltron, the Rheem RTEX 36 is also a premium product at a premium price. Only 5 years long limited warranty which is less than e.g. that of Stiebel Eltron.

Best Value for The Money Whole House – EcoSmart ECO 36


Ecosmart ECO 36

Pros: The cheapest in its category: 36 KW electric heaters with whole house level of GPM. Support is pretty good and helpful in case of any problem. Lifetime warranty.

Cons: Needs 4*40 AMPs breaker – may need to upgrade panel. Some people reported that sometimes it just turns off. 

Best Value for The Money Overall – EcoSmart ECO 11


EcoSmart ECO 11

Pros: You won’t find anything better for under 200 bucks. Lifetime warranty. Actually 13 KWs at 240 Volt and 11 KWs at 220 Volts. Small even among tankless water heaters.

Cons: Not a whole house unit. The list pretty much ends there – it is almost perfect for what it was supposed to be used.

Amazon Buyers’ Favorite – Stiebel Eltron Tempra 24 Plus

Stiebel Eltron Tempra 24

Pros: Amazon buyers seem to love this one. Over 75% of the reviews are 5 star which is pretty rare. It is pretty much the same as the Tempra Plus 36 with lower power usage and GPM. 

Cons: Won’t work as a whole house unit in a bigger house for a family of let’s say 5 or more people.


The product price for whole-house units is usually somewhere between 250 and 600 dollars.

In some cases the installation costs exceed the of the unit itself. There are two main scenarios:

  • 120-volt outlet is needed and available: 170 – 320 dollars
  • 120-volt outlet needed and must be added: 270 – 350 dollars
  • 240-volt outlet is needed and available: 320 – 650 dollars
  • 240-volt outlet is needed and must be added: 550 – 800 dollars


What brand should you go for? Is brand a deciding factor when looking for a tankless water heater? These are questions that often pop up in the mind of those thinking about buying any water heater actually, tankless or with a storage tank. It is a question that comes up pretty often for a good reason: there are quite some well-known tankless water heater manufacturers selling at different price points. Let’s dig in!

Even if this is the very first article you read in the topic, you have already met quite some brands – in the previous “best gas and electric tankless water heaters” sections. EcoSmart, Takagi, Stiebel Eltron etc. These brands may not mean anything to you because they are pretty much unknown outside the topic of water heaters and maybe some other kinds of home improvement products. One thing you can be sure of is that there is a good reason why they made our list of best in their category.

Back to the questions: The answer to what brand you should go for depends on your specific needs and whether the products of the given manufacturer meet those or not. It is true because most of the water heater manufacturer specialize in one given kind of product:

  • storage tank or tankless
  • electric or gas-powered
  • whole house or point-of-use

This fact makes your decision making a little simpler. First, you should know what exactly you need and what your budget is for it. Once you know these things you can go and look for a water heater that meet your requirements. Surely, you won’t end up with many brands to choose from.

Electric VS Gas Tankless Water Heaters

  • The very first thing you need to decide whether you are going to buy an electric or a gas tankless water heater. There are quite big differences between the two types. Let’s see!

Electric Models’ Features

  • Electric tankless water heaters are generally speaking cheaper than gas powered ones. However, the list of pros pretty much ends here.
  • Electric models with an acceptable GPM (gallons per minute) rate usually require 240 volt to operate so, it is possible that you need to upgrade your electrical system just to be able to use it. Such an upgrade may cost quite a big sum of money.
  • Their GPM is usually smaller than that of gas models. As a result, gas models are better whole-house solutions.
  • Electric tankless water heaters are also more expensive to operate than gas-powered ones. They consume a lot of energy when heating up the water flowing through the system. Bottom line is be ready for big electricity bills.
  • They are also not the best option for areas where ground water is cold. What does cold mean? Normally, if you live in an area where the difference between the temperature of inlet water (ground water) and the temperature to which water should be heated is greater than 40 degrees Fahrenheit, electric models are probably not the ideal solution for you.
  • There is one occasion when a small 120 volt electric heater can be useful. As an addition to a whole house solution. When a point-of-use unit does the job. A cheap electric model may be a better choice in such a case compared to a more expensive gas-powered one.

Gas Models’ Features

  • Gas tankless water heaters are more expensive to buy but cheaper to operate than electric models. Logically, the more hot water you use in the longer term the lower the total cost associated with the water heater will be compared to any electric models.
  • Ergo, it is usually worth spending more on the heater in the beginning because you will save more in the long term compared to how much more you spent on buying it.
  • Gas heaters have higher GPM rating. This makes them the better whole house solution.
  • They are also better at heating up water. They can basically heat up more GPM at less cost. Not only that, they are also the ideal solution in cooler areas where the inlet water (ground water) has to be heated up by more than 40 degrees Fahrenheit.


Everything You Need to Know About Gallons Per Minute (GPM)

We write a lot about GPM on this site. There is a very good reason for that. This is one of the most important specs you need to consider when choosing a water heater. Get this wrong and you won’t get the level of comfort you want and deserve.

GPM tells you how much water a given tankless water heater can heat up in a minute. It is not a static value. It varies depending on the temperature of inlet water and the temperature to which inlet water has to be heated up by the water heater (also called outlet temperature).

Let’s see an example. Here is a chart made by EcoSmart, one of the most popular tankless water heater brands who specialize on electric models:

GPM chart by EcoSmart

On the top right you can see a map of the United States where the different colors symbolize the average minimum inlet water temperature of the given area. Logically, the norther you go the colder the inlet water will get. Which also means that the norther you go the more powerful unit you will need to be able to heat the same amount of water up to the same temperature.

On the top left part of the picture you can see a part called “Application key”. Here you can see a min-max and an average GPM estimation for how many gallons of water different faucets and a shower require per minute.

Last but not least you can see a sizing chart. It was specifically made for the 7 Ecosmart electric tankless water heater models. However, it is perfect for showing you the logic. Based on the earlier mentioned map you can locate yourself and determine the expected minimum temperature of inlet water. Once you have this number in degree Fahrenheit you need to know the desired outlet water temperature – the temperature to which the inlet water should be heated.

What we are really interested in is the difference between the temperature of inlet and outlet water. EcoSmart used 105 degrees Fahrenheit as the target outlet water temperature.

So, in the sizing chart you can see how much GPM each EcoSmart model is capable of with given inlet water temperature (remember, outlet water temperature in this case is set to 105 degrees Fahrenheit). You can also see what it means in terms of usage.

For example: At an inlet water temperature of 52 degrees Fahrenheit, with outlet water temperature of 105 degrees Fahrenheit (a difference of 53 F) the expected GPM of the EcoSmart 27 is 3,4. It is enough to provide hot water to a shower and a bathroom faucet at the same time.

Be aware that some manufacturers like to show only the maximum possible GPM figure which is usually based on pretty warm inlet water temperature. Always evaluate the performance of the given water heater based on the characteristics of your location. When we do reviews on PrimeHeaters.com we always include these information so, you don’t need to go any further.

What Size Tankless Water Heater Should I Buy?

When it comes to tankless units the better question is how powerful heater should you buy – because almost none of the models require much space. So, size is not really a question or factor to consider in case of tankless water heaters – unlike storage tank heaters where the size of the tank may be one of the deciding factors.

Fun Fact: Did you know that GPM is actually restricted by the US Department of Energy? As you can see on the image below the maximum allowed GPM for shower heads for example was set lower 3 times since 1980.

Shower head gpm flow restrictions over the decades

Whole house VS Point-of-Use Tankless Water Heaters

Unlike size, this is a valid question. Not a very difficult one though. It all comes down to what you need the water heater for. Do you need it to provide hot water to several locations in a house, sometimes at the same time? Then you need a whole house unit. Or do you need a tankless heater to provide hot water to just one room and/or one faucet? You can go for a much cheaper point-of-use unit.

Point-of-use units are smaller, cheaper and less powerful (less GPM) than whole house heaters. Unlike whole house models, they are usually electric models (which by the way are generally cheaper than gas-powered ones). Some point-of-use electric tankless water heaters require 120 Volts and not 240 Volts which makes them more economic than e.g. whole house electric units running on 240 Volts.

Indoor or Outdoor?

Next, you’ll want to consider where you wish to install your water heater. Some people will want to install it inside, but this is not necessary. Installing the unit outside is a good way to maintain the spaciousness of your home, but it will undoubtedly alter your home’s appearance. An indoor heater is ideal for those that want to have immediate access to it in case of emergencies and malfunctions. Many believe that gas is best outside, since it’ll let you avoid installing any type of ventilation – which may save you hundreads of dollars. Then again, if you have already got the proper ventillation, this is not something you need to think about.


There is one more thing we need to mention when talking about buying a new tankless water heater: installation and costs related to it. Because there definitely are costs related to it: it has to be and can be done only by a professional. Not only that, but depending on what kind of tankless heater you buy and what the requirements of it are for actually working, you may also need to have some things in your home modified (electrical system, gas tube system, new ventilation etc.)

Professional Plumber installing an indoor tankless gas water heater

As we have written in our storage tank vs tankless water heater comparison article, the installation of tankless water heaters is generally speaking more expensive than that of storage tank models – simply because it is more complicated. Once you’ve decided about the water heater you should ask a professional about approximate installation costs. You can do it via our free online inquiry page. Fill it out with your details and ask for quotes from plumbers in your area. It is completely free and you won’t have any obligation to hire anyone: Click here for filling out the free quote!