In this guide, you will learn about TOP-6 best tankless hot water heaters and the technologies applied in production of these devices. Find out the differences between their main types — electric and gas devices — and in which situations either of them should be preferred. The guide will also tell you what are the important criteria to look for when shopping for such a machine. While a chart featuring these products will allow you to compare their strong and weak points in order to make the right choice.

What You Will Learn From This Guide:

What Are Tankless Water Heaters?

A Roman engineer once said, “Until taught by pain, men know not what good waterworks”. There’s a lot of truth to unpack from this quote, and from the era when it was allegedly said. Water is obviously a very important substance – almost no life on this planet can exist without it. Crops will not grow without it, and a lack of clean water can result in disease and other health issues.

Hot water has until relatively recently in history, been something that took a lot of labor to produce, unless you lived near hot springs (which remain a major destination for travel despite things). Fires had to be built, and water heated in cauldrons or other containers, making a hot bath something of a luxury – hence people bathing perhaps once a week in ancient times.

Today, we take hot water for granted, and this goes double for the technology behind it – the modern water heater. The first modern implementation of these was a small tank built into ranges in the Victorian era, which might heat enough water for one person to have a bath. These came with problems of keeping those range fires kindled, at least on a hot coal level, on a continuous basis, which was really … pleasant during those hot summer months.

Modern models – using gas or electric, are very much a 20th-century innovation, and one that came along in the late 1920s, for consumer use. They were ridiculously expensive, and even today, with modern innovations in efficiency and materials, a typical device has its problems.

A water heater with a tank has to work constantly to maintain a temperature in this large volume of water, which burns gas or uses electricity steadily. When the tank’s contents are depleted, there is simply no hot water until the tank can refill, and re-heat the water, as well. It’s a buffered system.

The concept of a tankless options has been something of a holy grail for engineers working in this industry pretty much since the concept of gas or electric units became a common concept. Today, the technology does indeed exist, with flash-heating of the water as it cycles through being possible.

I want to point out that this technology is far from perfect, and it absolutely is not a substitute for a traditional option in homes with three or more bedrooms, and more than maybe two occupants. If you’re expecting to do away with your tank heater in a typical family home with your nuclear family, it’s just not happening without multiple units and probably a higher gas or electric bill. I’ll get into why shortly.

Nonetheless, this technology does have its uses, its place, and its advantages. Today, we’ll learn about how they work, what to look for in these products, and six of the best ones (three electric and three gas). I also want to share a cautionary tale about these as well.

How Do Tankless Water Heaters Work?

Ultimately, the technology behind these is very simple, their being impossible for so long coming down to electronics components and materials sciences, not in them being complex on a basic level. To understand what’s unique about these, let’s first talk about how a regular hot water heater works.

It has a large tank which fills with water, and a line out to feed hot water into the building’s system. Inside this tank is a heating apparatus that dumps thermal energy into the water to keep it at a specific temperature. This is done in one of two ways – the most common being tungsten elements that’re heated by electricity (similar to electric oven elements or stove burners), or directional heat from natural gas combustion.

Tankless models obviously eliminate the tank, but that doesn’t mean there’s no reservoir wherein the water sits before being released. They have small chambers which fill with small amounts of water which is very, very rapidly heated by more powerful heating elements or gas combustion. Basically, it pours a lot more energy into a much smaller area. If you have a lot of hot water usage going on, this consumes a lot more energy. If you don’t, then it may be less energy usage, due to the fact that it’s not working to maintain a temperature in a large tank of water continuously.

What are the Types and Their Differences?

There really aren’t that many differences with these devices beyond the form of heating that they use. There are basically two types: gas and electric.

Gas heaters obviously work on natural gas, which is convenient if you already have a gas system connected to your home for heat and/or a stove/oven. If you don’t have a gas system already present, it could be a pain in the butt to implement gas just for one of these. One solution here is to hook small propane tanks to the intake line, which provide local heat sources for these devices. However, given the bursts of intense energy use that this technology needs, expect to have to replace these gas tanks somewhat often if you use a lot of hot water. It’s a somewhat cheaper solution, though, as natural gas is a renewable resource to some extent, and thus not a terribly expensive one.

Electric heaters are easier to get working and are less maintenance. They simply need to hook into appliance supplies of 110v or 220v sources. They do use significant power while they run, but as said before, they only really use this power when there’s a demand for hot water. Depending on how often you need hot water, and how much you use at a time, this may or may not use more electricity than a traditional tank unit.

Aside from this, the main distinctions are controls, speed by which they can heat up the initial flow of water, and so on. These vary from one unit to the next, so you can’t really categorize them in this sense.

What to Look for When Buying?

So obviously, when you’re buying any kind of water heater, you want to make wise decisions. Hot water is something very valuable to modern life. You can’t clean your clothes well without it, you can’t take a hot bath or shower, you can’t wash your hands, and you can’t wash your dishes either.

So, obviously, you want to look through some important criteria when you shop for a machine that provides this vital utility to your home, lest you regret it, and be out of a lot of money, as no model is truly cheap.

  • Heat Source – Obviously, you have to expend energy to get hot water. This is achieved either by burning fuel or by using electricity. Depending on your home, your budget, and your hot water demands, gas or electric may either one be ideal for you, it truly depends on your situation.
  • Rapidity – How fast can it get to a point where it’s outputting actual hot water? It takes a minute for the chambers to heat, and for it to get that small, dynamic supply of hot water flowing. It will probably be a little longer than for tank models to just get water into the lines, but by how much can vary wildly. Are you impatient, and value quickness over energy efficiency? Then be sure you pick one out that can get moving quickly.
  • Controls – You want to be able to control the temperature and if possible, the energy usage in some ratio with these. You can do this with a tank model, and so you want easy digital controls for a tankless one too. You also want these settings to withstand power hiccups, and I’ll have more on that shortly.

My Personal Experience

I won’t lie to you, I am not a huge fan of these for homes – at least not in a bathroom, because I’ve had some issues with these in the past. As I’ve said, I live in Florida now, and one of the biggest problems in Florida comes about during the summer when everyone is running their air conditioners at full blast. This puts a lot of stress on the power grids, so little brownouts on a daily basis aren’t uncommon. It’s just enough to be annoying – resetting your clocks and your computer, but the outages seldom last more than a few seconds.

However, with a tank model, most of which have analog temperature settings, the hot water already in the tank, stays hot, so there’s no disruption to it. And, the settings remain the same.

Well, one of the first places I lived down here, I rented part of a duplex, from a woman who installed tankless heaters in both kitchens and bathrooms, not out of “cheapness” but out of expecting it to be more efficient – she had two other people on her side of the house, I, however, had my half delightfully to myself at least.

Well, I learned quickly that these devices can have a downside when those obnoxious brownouts happen. I hadn’t had a shower in two days, from having been in the hospital for food poisoning. I still felt lousy, and when I got home, all I could think about was a nice, relaxing hot shower.

And at first, it was indeed wonderful. Then, a brownout happened. It was one of the longer-lived ones, being about five minutes long. I just shrugged it off initially, because usually, hot water continues to work unless the power is out for a long time, which I knew wouldn’t be the case.

Well, the first thing that happened was the hot water devolved into cold water – well cold for a shower, at about 68-70 degrees give or take. It made me gasp so sharply, I inhaled a bit of water. So there I stood for a few minutes choking and gasping – already still feeling like death warmed over from the aforementioned food poisoning, in freezing water.

Power came back on, and very suddenly, I was blasted with intensely painfully hot water, as the device had reset to a ridiculous temperature well over 110 degrees. Imagine someone flushing the toilet while you’re in the shower, magnified by a thousand.

Downsides & Problems with Tankless Water Heaters

So, this results in three cautionary things. First, don’t use these in an area where the tap water is under about seventy degrees, it works them very hard, and should there be a pause in the hot water flow, wow is it cold. Second, make sure the thing can remember your settings if there’s a glitch in the power unless you want to be boiled like a Maine lobster when the power kicks back on. Finally, don’t use these if you’re in an area that has lots of brief or even moderate length power outages unless you’re using a gas one.

I honestly don’t recommend these for normal residential use most of the time, really.

And if you want to choose the right tank model, take a look at my review of the Best Tank Heaters.

TOP-6 Best Tankless Hot Water Heaters

Take a look at a review of TOP-6 best products within the price range from $150 to $550. These are devices powered either by gas or electricity. While the former are suitable for heating and water supply of large premises, such as a house, the latter are less powerful and recommended for using in places like bathroom and kitchen. To understand whether a device will be suitable for you, consider GPM — a term that stands for “gallon per minute.” Gas models have a much higher GPM, however, they have a drawback of being relatively unsafe.

Best Electric Tankless Water Heaters

These devices are less powerful than gas ones but have the advantage of not needing their fuel to be refilled, and are simpler (and generally safer) affairs.

Basic Example of Electric Tankless Water Heater | Marey ECO110

Electric Tankless Water Heater Marey: photo

This is your quintessential tankless model with a basic control system for power and temperature adjustment. It uses partially nonvolatile memory, which means that unless there’s a prolonged power outage, at least the temperature settings will stay put.

This is intended for small scale use in areas where the tap water temperature is over seventy degrees and will work alright for showers or kitchens in those settings. 

Features

  • Multiple Use Points: Up to two.
  • Voltage: 220v appliance voltage.
  • Sustained Settings: Yes, unless power is out for a very long time.
  • GPM: 1.3 in cold regions (at one usage point), 2.6 in warmer regions (at 1.3 per usage point).
  • Power Source: Mains voltage (house electrical).

Performance

This one exemplifies the pros and cons of electric tankless models in general. It’s fine for the kitchen pretty much anywhere, though it may have a hard time keeping up with a dishwasher. However, for a bathroom, it’s only suited for use in warmer regions where it doesn’t have to work especially hard to heat the water and maintain a flow for heavy use. 

If you live here in Florida, or in the South West, you might be okay with two of these in your house, though power interruptions will cause the water to go almost instantly cold. Marey is a respected manufacturer of this sort of technology, though, so you know you’re getting reliability and durability.

Pros Cons
  • Affordable.
  • Simple.
  • Reliable manufacturer.
  • Two use points in warmer climates.
  • Compact.
  • Good controls. 
  • Persistent settings.
  • Not fit for bathrooms in cold places.
  • Really not fit for a family or larger house.

Conclusion 

I’m okay recommending this for kitchens, or for half baths where you only have hot water in a sink, but as will be the case with many of these, I say don’t use these for showers or laundry.

Marey ECO110: Check the current price

Professional Model of Tankless Water Heater | Rheem RTEX-13

Tankless Water Heater from Rheem: photo

If you’ve ever worked with utility appliances at all, you know that Rheem is a damn good, reliable brand overall. Their products are sought after. Their little red circle with a unique font is more or less a seal of quality when it comes to utility appliances in the west.

This one has a simple persistent setting system with a nob and has a bit more oomph than some of the others, and as you’ll see, is one of the few I am okay with recommending for houses.

Features

  • Multiple Use Points: Up to two.
  • Voltage: 220v appliance voltage.
  • Sustained Settings: Yes, unless power is out for a very long time.
  • GPM: 2.6 with two access points in cold or warm climates.
  • Power Source: Mains voltage (house electrical).

Performance

Rheem is an example of a much more powerful tankless electric heater, capable of keeping up actually with the demands of a bathroom, though even this professional/residential model is probably not enough for an entire house.

However, two of these in an average house, one for the kitchen, one for two bathrooms, would almost certainly keep up with demands mostly. Despite Rheem’s quality, though, I’m still not sure about these for the level of demands a household has.

Pros Cons
  • Simple.
  • Reliable manufacturer.
  • Two use points in warmer climates.
  • Compact.
  • Good controls. 
  • Persistent settings.
  • Expensive.
  • Really not fit for a family or larger house.

Conclusion 

This one I am a lot more comfortable with recommending for the demands of an actual family, than most other devices like this, electric or gas. However, I still advise two of these if you have more than one person in the house, and you do use a lot of hot water, as physics is physics.

Rheem RTEX-13: Check the current price

Green Electric Tankless Water Heater | EcoSmart ECO 27

Green Electric Tankless Water Heater: photo

Okay, let me preface this one with saying that I am all for being ecologically smart, because we really are destroying this planet, and I’m tired of the baby boomers’ mess causing it to be so damn hot outside of late. However, there’s a problem with things engineered around ecological wisdom as a central focus – it tends to be weak.

EcoSmart is a brand that’s usually pretty good at squeezing the juice out of “green” systems, but you’re going to find that this thing really can’t keep up with more than a kitchen.

Features

  • Multiple Use Points: Up to two.
  • Voltage: 240v appliance voltage.
  • Sustained Settings: Yes, unless power is out for a very long time.
  • GPM: 1.6 with two access points more or less.
  • Power Source: Mains voltage (house electrical).

Performance

As I said a moment ago, these “green” solutions tend to be underperforming, and that’s the case with this EcoSmart model, though it does a better job than competing companies with this focus. We need to solve the environmental issue by how we generate power, not so much how we use it.

Pros Cons
  • Simple.
  • Reliable manufacturer.
  • Two use points in warmer climates.
  • Compact.
  • Good controls.
  • Persistent settings.
  • Weak.

Conclusion 

I only recommend this for the kitchen or a small trailer, and only if you’re that much of a green person. This is an underperforming device. I don’t really like this one.

EcoSmart ECO 27: Check the current price

Best Gas Tankless Water Heaters

They tend to be faster and more powerful, but require replenishing of fuel, are bigger, and have some dangers inherent to them – it’s gas and gas explodes, you know.

Standard Model of Tankless Gas Water Heater | Eccotemp i12-NG

Eccotemp Tankless Gas Water Heater: photo

Eccotemp is another example of ecological focus, but it’s less of an issue when you’re burning fuel – it focuses on wasting as little heat from burning the gas as possible, rather than trying to squeeze value out of voltage.

Features

  • Multiple Use Points: Up to two.
  • Voltage: N/A.
  • Sustained Settings: Yes, unless power is out for a very long time.
  • GPM: 3.6 with two access points more or less.
  • Power Source: Gas (voltage for control board).

Performance

Once again, eco-smart things tend to be weaker, though in the case of combustion technology, it’s not as much of a problem, as it tries to get more heat per unit of fuel, rather than counting every electron, which isn’t the same.

This is a much more powerful device than any electric one, and this will indeed work for a small household.

Pros Cons
  • Simple. 
  • Reliable manufacturer.
  • Two use points in warmer climates.
  • Compact.
  • Good controls.
  • Persistent settings.
  • Gas can be dangerous.
  • Requires fuel.

Conclusion 

Gas has inherent risks, which will be the case for all three of these, but I am fine recommending this for a smaller household.

Eccotemp i12-NG: Check the current price

Indoor Propane Tankless Water Heater for Large Families | Takagi T-KJr2

Indoor Propane Tankless Water Heater: photo

Takagi isn’t as well-known in the west, but in the industry, has a very established, and positive reputation.

This is a rare case of one that I feel actually could handle the demand of a large family with multiple sources straining it. It’s a fuel guzzler, though.

Features

  • Multiple Use Points: Up to two.
  • Voltage: N/A.
  • Sustained Settings: Yes, unless power is out for a very long time.
  • GPM: 6 with two access points more or less.
  • Power Source: Gas (voltage for control board).

Performance

I’ve pointed out how these are often just not able to handle the demands that a tank model is meant for, but this is one of the rare cases where an exception can be made. The next one on the list also meets these criteria but might be a little more costly.

Pros Cons
  • Affordable. 
  • Reliable manufacturer.
  • Two use points in warmer climates.
  • Compact.
  • Good controls.
  • Persistent settings.
  • Gas can be dangerous.
  • Requires fuel.
  • Gas guzzler.

Conclusion 

This one will definitely provide steady hot water for an average household, though if you live in an area where gas is expensive, this may run you a high bill to do so.

Takagi T-KJr2-IN-NG: Check the current price

Best Safe Indoor Tankless Propane Water Heater | Rinnai V65IN

Safe Indoor Tankless Propane Water Heater: photo

This one is very powerful too, and Rinnai is another one that’s not as well-known in the west but is reputable within the industry. Rinnai’s model is focused on safety, which is good. As I’ve pointed out, gas has inherent dangers, such as carbon monoxide.

Features

  • Multiple Use Points: Up to two.
  • Voltage: N/A.
  • Sustained Settings: Yes, unless power is out for a very long time.
  • GPM: 6.6 with two access points more or less.
  • Power Source: Gas (voltage for control board).

Performance

This is a beefy heater, and its focus on safety means that you can feel at peace with the device and the power source. Gas is something many fear, and it is something that deserves caution and respect.

Pros Cons
  • Affordable.
  • Reliable manufacturer.
  • Two use points in warmer climates.
  • Compact.
  • Good controls.
  • Persistent settings.
  • Very safe.
  • Gas can be dangerous.
  • Requires fuel.
  • Gas guzzler.
  • Needs extra ventilation due to its exhaust system.

Conclusion

This is the hardest one to set up because of extra needs, but it’s tremendously powerful, and very, very safe compared to other gas appliances. I am okay recommending this one if you insist on a tankless option.

Rinnai V65IN: Check the current price

Comparative Chart of Tankless Water Heater Effectiveness

Product Features

Marey ECO110

• Multiple Use Points: Up to two.
• Voltage: 220v appliance voltage.
• Sustained Settings: Yes, unless power is out for a very long time.
• GPM: 1.3 in cold regions (at one usage point), 2.6 in warmer regions (at 1.3 per usage point).
• Power Source: Mains voltage (house electrical).

Effectiveness: 8

Rheem RTEX-13

• Multiple Use Points: Up to two.
• Voltage: 220v appliance voltage.
• Sustained Settings: Yes, unless power is out for a very long time.
• GPM: 2.6 with two access points in cold or warm climates.
• Power Source: Mains voltage (house electrical).

Effectiveness: 10

EcoSmart ECO 27

• Multiple Use Points: Up to two.
• Voltage: 240v appliance voltage.
• Sustained Settings: Yes, unless power is out for a very long time.
• GPM: 1.6 with two access points more or less.
• Power Source: Mains voltage (house electrical).

Effectiveness: 10

Eccotemp i12-NG

• Multiple Use Points: Up to two.
• Voltage: N/A.
• Sustained Settings: Yes, unless power is out for a very long time.
• GPM: 3.6 with two access points more or less.
• Power Source: Gas (voltage for control board).

Effectiveness: 8

Takagi T-KJr2-IN-NG

• Multiple Use Points: Up to two.
• Voltage: N/A.
• Sustained Settings: Yes, unless power is out for a very long time.
• GPM: 6 with two access points more or less.
• Power Source: Gas (voltage for control board).

Effectiveness: 9

Rinnai V65IN

Safe Indoor Tankless Propane Water Heater min: photo

• Multiple Use Points: Up to two.
• Voltage: N/A.
• Sustained Settings: Yes, unless power is out for a very long time.
• GPM: 6.6 with two access points more or less.
• Power Source: Gas (voltage for control board).

Effectiveness: 10

FAQ 

What is the best tankless water heater?
Rheem for electric, Rinnai for gas.

Can it be installed outside?
Yes but preferably don’t.

What temperature should a tankless water heater be set to?
Between 100 and 110 F.

Can it be installed in a mobile home?
Yes.

Can water heaters leak?
Sure, anything can if it’s damaged or not connected right.

Pros & Cons of Using These Products

Pros

  • If you don’t use a lot of hot water, they can be power-smart.
  • They’re smaller, requiring less space.
  • They can be distributed to different rooms.
  • They can increase the resale value of a home.

Cons

  • They are susceptible to power outages.
  • They have to work hard to provide water while running.
  • They take longer to get hot water flowing.

Conclusion

If you want a tankless solution, I’m confident that one of these will suit your needs. Both tankless and tank heaters have their flaws. Either way, sometimes you need one of these, and one of these models will be right for you.