10 Best Tankless Water Heater in 2022 – Reviews with Buying Guide

Best Tankless Water Heater: When it comes to hot water heaters, there really is no debate: everyone needs one, and it doesn’t matter where you live. Nothing beats a hot shower, right? We depend on hot water each day in our homes, from washing dishes to washing laundry, to baths. Hot water boilers make it all possible.

Now, when I say on demand hot water heaters, you’re probably envisioning one of those huge 7 feet tall metal tanks that essentially sits on top of a big gas range, constantly lighting up throughout the day to keep the water inside hot. That’s understandable, as these have been the conventional choice of most households for years.

However, have you ever run out of hot water in the middle of a shower? Or dealt with that cold blast of water because someone elsewhere in the house flushed a toilet, or decided to start a load of laundry? Of course, you have. Nobody enjoys that.

Did you know there’s a better way?

Tankless hot water boilers avoid the trouble of having a finite amount of hot water stored away in a tank, in constant need of reheating. These small, yet powerful devices can instantly turn cold water from your home’s incoming plumbing into an endless supply of piping hot water that’s always readily available right when you need it.

Intrigued? You should be. Think these are too expensive for you? Think again.

Tankless hot water heaters come in a variety of sizes and types, ranging from immensely powerful models that provide hot water for entire hotel room floors, to smaller versions you can easily install in your home with little fuss.

As an experienced HVAC professional, I’ve dealt with my fair share of tankless hot water boilers over the years, and have gotten to know them well. In fact, I use them in my home, and now I’m going to show you the 10 best water heater models currently available, spanning many different sizes and price points.

So, if you’re in the market for a water heater, or are simply curious about what they can do for you, read on to see my picks, as well as some helpful buying advice.

Let’s get started, shall we?

Best Tankless Water Heaters Reviews for 202

Top Choice
Stiebel Eltron 224199 240V, 1 Phase, 50/60 Hz, 24 kW Tempra 24 Plus Whole House Tankless Electric Water Heater, Advanced Flow Control
EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology
Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater
Camplux 10L Outdoor 2.64 GPM Digital Display Portable Propane Gas Tankless Water Heater
Stiebel Eltron 224199 240V, 1 Phase, 50/60 Hz, 24 kW Tempra 24 Plus Whole House Tankless Electric Water Heater, Advanced Flow Control
EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology
Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater
Camplux 10L Outdoor 2.64 GPM Digital Display Portable Propane Gas Tankless Water Heater
from $539.00
from $194.13
from $179.00
Prime Delivery
Top Choice
Stiebel Eltron 224199 240V, 1 Phase, 50/60 Hz, 24 kW Tempra 24 Plus Whole House Tankless Electric Water Heater, Advanced Flow Control
Stiebel Eltron 224199 240V, 1 Phase, 50/60 Hz, 24 kW Tempra 24 Plus Whole House Tankless Electric Water Heater, Advanced Flow Control
from $539.00
Prime Delivery
Buy Now
EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology
EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology
from $194.13
Prime Delivery
Buy Now
Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater
Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater
Prime Delivery
Buy Now
Camplux 10L Outdoor 2.64 GPM Digital Display Portable Propane Gas Tankless Water Heater
Camplux 10L Outdoor 2.64 GPM Digital Display Portable Propane Gas Tankless Water Heater
from $179.00
Prime Delivery
Buy Now

Winner, Best Overall Tankless Hot Water Heater: Stiebel Eltron Tempra Plus (Electric)

Stiebel Eltron Tempra Plus

For those that think you have to spend a ridiculous amount of money in order to have a fully functioning hot water convector that can support multiple water sources at one time, the Stiebel Eltron Tempra Plus begs to differ.

While this unit is certainly not cheap, it still costs less than several other water heaters that advertise themselves as superior, while providing a top-tier level of performance that’s hard to find elsewhere — one of the many reasons it’s our overall favorite for the best tankless water heater.

The Tempra Plus is electric-powered, so you don’t have to worry about using a gas source. The unit is relatively small when considering the power output, and it requires absolutely no ventilation whatsoever. It’s available in a wide range of wattages, helping you better match it to your actual climate.

The water temperature is displayed digitally in an easy-to-read manner, and the temperature can be controlled with a dial that tells you what each setting is best for. Auto-modulation allows for ideal temperature control without exerting too much energy, helping you save on your bill.

Constant and quick heating is provided by dual copper chambers that help you avoid the dreaded cold spurts that can sometimes interrupt your hot water flow, especially when other sinks and showers are being used at the same time.

A minimum flow rate of 0.5 gallons triggers the unit on, and depending on your outside water temp, it can provide around 5 gallons per minute at whichever temperature setting you’ve selected.

You may notice that there is a Tempra Plus, and just an ordinary Tempra. The “Plus” indicates that it comes with Advanced Flow Control, which restricts the water pressure as needed in case there is a lag in maintaining the water’s heated temperature. This is definitely preferred over the cold spurts you get with models that can’t offer such a feature.

As far as disadvantages go, it’s hard to really pinpoint any with a unit of this quality and price. Having a digital temperature control would be welcome, and maybe a slightly smaller unit, but this is really just being picky for the sake of being picky. No major flaws here.

The Stiebel Eltron Tempra Plus is simply the best you can buy for under $1,000. And depending on your needs, you can purchase the unit in smaller or larger sizes to better match the water sources in your property. If you’re aiming for the best, definitely start here — you can’t go wrong.


  • Powerful
  • Advanced temp control avoids cold water surprises
  • Digital temperature read out
  • Suggested heat settings
  • No ventilation needed


  • Price
  • A little big for some spaces

Check Price on Amazon

Best Tankless Water Heater Electric: EcoSmart ECO 27

EcoSmart ECO 27

For many, one of the biggest allures to using a tankless hot water heater is the energy-saving aspect. While the most energy-efficient heaters sometimes involves sacrificing the overall effectiveness and capabilities of a unit, that’s not the case with the EcoSmart ECO 27.

This innovative, powerful tankless hot water convector is capable of supplying hot water to a number of different outlets in your home, while not only maintaining even heating throughout, but also at a significantly reduced energy rate during the duration of its use.

The ECO 27 is one of the smaller units you’ll come across, at least in terms of ones that can supply the amount of hot water as this model. Its smaller footprint makes it suitable to be mounted where your hot water tank used to be, or as a point-of-use unit below a sink, or near a shower.

The unit’s temperature is displayed directly on the front of the box with a digital readout, and it can easily be controlled with the turning of a dial, right down to one degree at a time — anywhere in between 80 degrees and 140 degrees Fahrenheit.

The minimum flow rate to activate the ECO 27 is 0.25 gallons per minute, so a dripping faucet will not unintentionally turn it on. For this model, you can expect about 2.7 gallons per minute in colder climates, and up to 6.6 gallons per minute in warmer climates, or during the summer.

Most top-level hot water heaters have a modulation feature that allows the water temp to remain the same by altering the flow rate as needed. The ECO 27 is self-modulating, but does things a bit differently, using anywhere from 1 to 3 of its copper heating pipes at a time, depending on the incoming water, combined with the desired pressure on the other end.

This is what makes it “eco smart,” as the modulation features only uses what it needs in real time, helping keep energy costs down, and eventually even letting the ECO 27 pay for itself, sometimes within a years time.

The EcoSmart ECO 27 is easily one of the best tankless hot water heaters on the market, and for one of the best prices you’ll come across. Its combination of affordability, effectiveness, and low energy use makes it a can’t miss purchase on every level.

Check Price on Amazon

Winner, Best Budget Tankless Hot Water Heater: Rheem RTX-13 (Electric)

Rheem RTX-13

For those that want to keep the price down and need a powerful point-of-use model, or simply live in a warmer climate that doesn’t require a large unit, the Rheem tankless water heater RTX-13 is the best option in their expansive line of water heaters.

This small, yet powerful unit hardly takes up any space, is easy to install, and even easier to use. And while it may not crank out a high amount of hot water for multiple outlets at the same time, when used within its constraints it excels — especially well when considering the price. takagi tankless water heater

The RTX-13 has sort of a cool, modern look, and is very small in stature when compared to other models. Hoses are connected on each side, and the temperature dial and display are located in the center. The display is crisp and bright, and the dial adjusts temperatures one degree at a time, ranging from 80 degrees to 140 degrees Fahrenheit.

Although not technically Energy Star rated, I wouldn’t be surprised if the RTX-13 eventually achieves the rating officially. It used two separate copper pipe heating elements as needed, as the unit determines how much heating is needed as the water passes through, utilizing self-modulation for more energy efficiency.

This results in an average gallon per minute output of around 1.5, with a maximum of 3.17 in ideal conditions. In most cases, this is enough to run the shower and a faucet at the same time, with no hot water, drop off or flow reduction. Flow-optimizing shower heads allow the unit to be even more efficient, so keep that in mind.

While the RTX-13 is efficient and powerful, do realize that it’s not an ideal unit to use in a large house in the middle of winter. If you have higher water demands in a colder climate, you’re better off getting one of Rheem’s larger, more powerful models.

All in all, the Rheem RTX-13 is the best you can get when trying to spend less than $350 and still come close to supplying an average sized house with endless hot water throughout the year. Its surpsign energy efficiency, small profile, and economical price are more than enough reasons to keep it high on your buying list, if your living situation is appropriate for its size.

Check Price on Amazon

Winner, Best Portable Tankless Hot Water Heater: Camplux 10L (Propane)

Camplux 10L

Portable tankless hot water heaters are a bit of a different beast when compared to permanent models you install inside a home. While the concept is relatively the same, the application is not, so it’s best to know the limitations and advantages.

With that said, if you are requiring a powerful, reliable, and capable hot water boiler you can use on a camping trip, in your yard, or practically anywhere else you need to set one up, the Camplux 10L is the clear choice for a variety of reasons.

While many hot water heaters are powered by electricity and copper heating elements on the inside, the Camplux 10L takes the gas route instead, due to its need for portability. In this case, that power source comes from propane, not unlike what you see with a camping stove or boiler. You can go for hybrid water heaters if you want to save the gas or electricity bill.

To use the Camplux 10L, you simply hang it up in an outside location, attach the propane tank, and use either an electric outlet or two DD batteries for the flame’s ignition. From there, you can adjust both the water flow and the temperature using the dials located in the front.

The unit includes a shower hose to make things a little easier, or you can opt to use a standard hose. The same connectors are used for attaching the Camplux 10L to your water source. Depending on the inlet water temp, you can achieve up to 2.6 gallons per minute of water output with full water heat.

The Camplux 10L is intended for outside use, but it can be converted to an inside model bty installing a flue pipe to carry exhaust away from its location. This gives it an added amount of versatility, and makes it suitable for smaller cabins, homes, horse stables, etc. Want to use it on a modified water system? Connect it to a 12v pump and you’re good to go.

The main advantages with this system center around its overall portability, along with its ease of use, and surprising heat efficiency. This unit can definitely make campouts and outdoor stays a lot more luxurious, and you still have the option to use it inside.

Obviously there are going to be some limitations due to the design, but as long as you know what you’re getting going in, it shouldn’t be an issue.

The Camplux 10L is simply the best portable tankless hot water heater, offering a mixture of convenience and innovative design, which is reinforced with impressive heating ability, and ease of use. And with a price of just over $200, it’s a great bargain.


  • Portable
  • Powerful for size
  • Built-in shower head and hose
  • Usable inside and out


  • Not as conventional
  • More Great Buys

Check Price on Amazon

Titan SCR2 N-120 (Electric)

Titan SCR2 N-120

Not every tankless hot water heater buyer needs a giant unit that can deliver scalding water in the dead of winter in Canada. For those that have smaller homes, cabins, or guest houses in warmer climates, the Titan SCR2 N-120 is an inexpensive option that is capable of getting the job done.

As a small, compact electric-powered unit, you have a lot of leeway as to where you can install the unit, whether that’s in your water tan closet, or even as a point-of-use unit mounted below a sink or behind a shower.

The SCR2 N-120 measures only 10x7x3 inches, and weighs a mere 8 pounds. You’ll have no trouble mounting it, and won’t need a bunch of assistance in getting it installed. Nice and simple. Push buttons on the front allow you to change the temperature, with a graph display that lights up to indicate the setting, which starts at 105 degrees Fahrenheit.

As for the GPM, this tiny unit can put out 4 gallons per minute, but the inlet water temperature has to be above 65 degrees, so keep that in mind. Colder temps will result in low water pressures if you’re using a high flow appliance like a washer or shower.

The SCR2 N-120 maintains consistent water temps by using a sampling system that checks the temp 21 times in a single second, making small adjustments to the flow rate as it operates, ensuring the temperature always stays the same.

For many, the price point is the most attractive part of this unit, and that’s understandable. It’s cheap, yet packs a big punch in the right environment. The flow rate is excellent considering the size, and the water sampling system keeps things consistent — literally all you could ask of a tankless heater.

The only negatives are the high inlet water temp requirements, but again, this is geared towards warmer climates ands small homes/cabins, so this shouldn’t be an issue when used correctly. The high starting temp is a little odd, but doesn’t detract from things much at all.

If you’re looking to spend the least amount of money, live somewhere like Florida or Arizona, and have a smaller home or family, the Titan SCR2 N-120 may be just what you need.


  • Compact
  • Economical
  • Efficient for its size
  • Easy to install


  • Requires 65 degree inlet water
  • High minimal temperatures

Check Price on Amazon

Atmor 24kw/24V ThermoPro Tankless Hot Water Heater (Electric)

Atmor 24kw-24V ThermoPro

Looking for a point-of-use tankless hot water heater that doesn’t look terrible? The Atmor 24kw/24V ThermoPro is a perfect solution for those needing a reliable and capable water boiler they can install visibly in a bathroom or kitchen area, or simply the same location where their hot water tank used to be.

The ThermoPro is an electric unit that uses high-efficiency heating elements to create near-instant hot water in a variety of climates, using advanced sensors and flow control to ensure the temperature is always consistent, regardless of water output elsewhere

Temperatures can be controlled right on the front of the sleek-looking unit by using the chrome knob, allowing for adjustments in 1 degree increments — a rarity for nearly any hot water heater, regardless of type. The unit maxes out at 120 degrees Fahrenheit.

As with any tankless unit, the gallons per minute will depend on the inlet water temperature at that point of the year.  The ThermoPro has a maximum of 4.6 GPMs when used with an inlet water temperature of 73 degrees Fahrenheit. Colder climates will attain a GPM capacity of around 2.5 to 3, which is still enough to run a shower and dishwasher at the same time.

The ThermoPro is definitely striving to be the best in the style department, but this little unit packs a punch in terms of heating ability. While it’s still better for warmer climates, it can still deliver adequate water amounts during winter months in colder climates. This is further improved by using it as a point-of-use installation, but that’s not required.

The ability to change heat settings by 1 degree is awesome, and the large dial makes things even easier. Furthermore, the unit is corrosion-proof and spill-proof, making it ideal for point-of-use installations where it will be exposed near the water fixture.

The only real potential drawbacks here revolve around the actual installation It can be a little trivy if you’re new to the process, and you’ll aso have to check quite a few different aspects of your home’s electrical setup to make sure you can support the unit.

At just under $400, the Atmor ThermoPro is an efficient and surprisingly powerful tankless hot water convector with a very modern aesthetic. The more decor-conscious buyers will certainly appreciate a unit that combines both form and function — and for a fair price.


  • Sleek look
  • Easy temperature adjustments within 1 degree
  • Low price for the power


  • Complicated installation
  • Requires higher inlet water temps for better efficiency

Check Price on Amazon

Tankless Gas Water Heater Reviews

Best Tankless Gas Water Heater : Takagi T-KJr2-IN-NG

Takagi T-KJr2-IN-NG

Tankless on demand water heaters come in two distinct setups: gas, and electric. The majority of this list involves electric-powered models, but gas-powered versions are not to be overlooked. For many, this is actually a better option for homes with a conventional hot water boiler setup.

With that said, the Takagi tankless water heater T-Kjr2-IN-NG is one of many models in the company’s lineup, with this one being more of a mid-range model. But don’t let the size fool you. While this is a smaller, more compact version of larger Takagi models, this is also one of the most capable.

The T-Kjr2-IN-NG can be installed where your hot water tank used to be located, using the same gas connection. It’s larger than most electric units, but for a gas-powered model, it’s actually quite small, weighing just 38 pounds, and measuring 20x14x7 inches.

Water is heated as it passes through the unit by the way of gas-powered flames. Temperatures can range between 99 and 167 degrees Fahrenheit, depending on the ground temperature. Rather than using knobs, the T-Kjr2-IN-NG comes with a remote control to adjust temperatures as needed.

Thanks to its efficient design and gas power, the T-Kjr2-IN-NG can offer a GPM rate of up to 6, which is certainly more than most electric models in its range. In favorable conditions, it can supply hot water to homes with 2-3 bathrooms, allowing someone to shower, while the dishwasher is being run.

The T-Kjr2-IN-NG is a very feasible replacement solution for someone who wants to get rid of the tank and save on energy, yet not sacrifice on the amount of hot water they can immediately access without interruption or diminished temperature range.

The fact that is is so small provides advantages during installation, and for anyone with cramped space in their closet. I really like the use of a remote control as well. You don’t have to leave it sitting out if you’re worried about losing it, simply set it near the unit at all times and you’re fine.

As with any gas tankless boiler, you’ll need to properly ventilate the heat exhaust, so do keep that in mind. You also won’t get the same energy savings as an electric model, but it’s still a lot better than using a tank.

Overall, the Takagi T-Kjr2-IN-NG is probably the best gas water heater for the money. For just under $500, you can attain a very capable solution that provides a very high amount of gallons per minute, and at a fraction of the maintenance, replacement costs, and energy usage. This is a great unit.


  • High GPM
  • Energy Efficient
  • Small and Compact
  • Remote control


  • Requires Venting
  • Installation is more extensive

Check Price on Amazon

Best Natural Gas Water Heater: Noritz NRC98-DV-NG

Noritz NRC98-DV-NG

The Noritz NRC98-DV-NG is a massive tankless gas water heater for buyers needing to meet high water output requirements for larger homes and families. Powered by gas, this is as close as you can get to a conventional tank water heater’s performance — only without the tank.

The NRC98-DV-NG accomplishes this in several ways, but mostly through two different heating elements that work together to create instantly hot water with a huge output level. The first element serves as a pre-heater in a way, while the second element actually uses the heat exhaust to further heat the water. Genius, right?

Not only does this make the unit more efficient and quicker at heating, it also minimizes the amount of heat exhaust, which is one of the main drawbacks of a gas-powered unit. With this design, the exhaust is around 100 degrees Fahrenheit, which is a lot cooler than other models.

The NRC98-DV-NG is definitely on the larger side, measuring 24x18x10 inches, and weighing 58 pounds. It has three main heat settings, but you can access 9 settings by purchasing a remote, also allowing you to adjust the temperature by 5 degree increments. Temperatures range between 100 and 140 degrees Fahrenheit.

As for the gallons per minute? The NRC98-DV-NG can maintain an output of 9.8 GPM with favorable inlet water conditions. This makes it suitable for a variety of climates. Yes, using it in cold climates will affect its output, but you can still get around 4-5 GPM, the max of many other units.

The NRC98-DV-NG also has a lot of safety settings, including a flame sensor, overheating prevention, and freeze protection.

And while the unit does it the 4 figure price range, it will eventually pay for itself anyway. It’s large size and exhaust setup is probably better with professional installation as well, so you’ll need to factor that in to your budget.

Simply put, the Noritz NRC98-DV-NG is the most powerful tankless on demand gas water heater on this list. If you’re looking for a high output model that can sustain standard temps and pressure for multiple bathrooms and fixtures at the same time, this is the way to go.


  • Very powerful with high flow rate
  • Advanced safety settings
  • Works well in cold climates


  • Expensive
  • Requires remote purchase to access more temperature settings

Check Price on Amazon

Propane Tankless Water Heater Reviews

Rinnai RL75iN: Best Propane Tankless Water Heater

Rinnai RL75iN

For those looking for a tankless hot water heater that can really crank out a high amount of water, be it for home or commercial properties, the Rinnai RL75iN is definitely worthy of your attention. Another great example of a high output propane/gas-powered model, the RL75iN is up to task, and you don’t have to live in a warm climate to benefit.

The RL75iN is designed to take the place of your tank boiler in the spot it once occupied (or wherever you’d like to route gas lines.) And while it is a standard gas-powered unit, it does do things a little differently, mainly in being a high output model that can use natural gas or propane.

This unit can attain water temps anywhere from 98 to 140 degrees Fahrenheit, all of which can be controlled on the front of the unit with digital dials and readouts.It also offers error codes if something goes wrong so you know exactly what the issue is.

In terms of gallons per minute, the RL75iN can reach a whopping 7.5 GPM in ideal conditions, with a 5 GPM level in colder environments. This is all powered by anywhere from 10,300 to 180,000 BTUs, so this thing really is a beast.

If you have around 2-3 bathrooms in a moderate climate with cold winters, you won’t be lacking in hot water, even with two showers going at once. You can also convert the unit to a commercial model with a controller upgrade, reaching temps of 160 degrees. That’s hot.

The RL75iN comes with a giant 12 year warranty, with 5 years on parts, so it’s in it for the long haul. It’s one of the most powerful units on this list, and still manages to be Energy Star certified, which is hard to do, A scale detection system indicates when hard water is causing issue and requires a descaling cycle.

There are a few obvious drawbacks, mainly revolving around the price of the unit., but powerful models will always cost more for a reason. Ventilation can be tricky too, and you’ll need to make sure your gas line can offer enough pressure to reach 180,000 BTUs, so a reconfiguration my be needed.

As I’ve said, this is a massive unit that combines reliable water temps, versatility between fuel sources, ease of use, and built-in features that elongate the unit’s life. Rinnai RL75iN is the best propane tankless water heater and if a high GPM is your goal, the Rinnai RL75iN is worthy of your attention.


  • High GPM
  • Energy Star Certified
  • Awesome Warranty
  • Scale Detection


  • Large Size
  • Expensive
  • Venting may require a professional to assist

Check Price on Amazon

Eccotemp FVI-12-LP (Propane)

Eccotemp FVI-12-LP

Gas and electric tankless hot water heaters are well represented on this list, as they should be, but propane-only units can be every bit as useful, and not only in RVs and small cabins/vacation houses. The Eccotemp FVI-12-LP is a great example of a versatile and easy-to-use tankless hot water heater that can be used in a variety of locations.

As i’ve said, the FVI-12-LP is powered by propane, and you can actually use anywhere from 20 pound to 100 pound tanks, giving you the ability to tailor your tank size for how much the unit will be used. It has a standard 2-prong plug-in that powers the ignitor.

The FVI-12-LP uses dials on the front to control the temperature, which is digitally displayed for better accuracy, taking out the guesswork. The maximum setting is 120 degrees Fahrenheit. When plugged in, the unit only activates the gas when it sense the water flowing through, so you save on gas there too.

The GPM can range from anywhere between .09 gallons per minute, and 4.8 when used in warmer climates. This makes it suitable for small homes with low simultaneous water usage. 3.0 GPMs is more average for this unit, which it can attain when being used with a 55 degree rise.

The small size and simple design of the FVI-12-LP makes it ideal for point-of-use applications, but it can also be used as a typical tank replacement in warmer climates, or homes that use one water fixture at a time.

With a price of under $275, the FVI-12-LP is one of the most affordable you’ll find, while still offering the capabilities of supplying a decent amount of hot water to sinks, showers, tubs, and more. Yes, you’ll still be purchasing propane from time to time, but not as much as you’d think due to the impressive efficiency of the unit.

The FVI-12-LP also comes with its own vent kit, and is relatively easy to install, making the process even simpler and more ideal for small homes and vacation cabins. No, it’s not as powerful as larger units, and not as suited for colder climates, but when used within its range, it offers excellent value.

Overall, the Eccotemp FVI-12-LP provides as much as it can for the price. The propane-powered nature of the unit gives it more versatility as to where you can use and/or install it, making it a logical choice for warmer locations and smaller homes with less-used water utilities.


  • Affordable
  • Versatility due to propane power
  • Easy to install


  • Not very powerful in colder climates
  • Still requires electric outlet

Check Price on Amazon

How a Tankless Hot Water Heater Works?


I’m sure most people are familiar with conventional hot water tanks. The concept for these is fairly simple: water is stored in a large metal tank, which is heated on the bottom by gas flames. When the tank is heated to the desired temperature, the water remains in the tank, ready to use.

As water is depleted from the tank, more cold water is fed into the tank, where it’s then heated as well before eventually making its way to faucets, showers, dishwashers, etc.

With a tankless water heater, the water has no way of being stored, so it needs to be heated as it passes through from the source, and into the home’s various water outlets.

This is done in several different ways, depending on the type of tankless hot water heater. Electric models use heat elements, while natural gas and propane versions use flames to heat the elements and piping the water passes through. (More on that in a moment.)

Benefits of a Tankless Hot Water Heater

So, why would someone even want to mess with a tankless hot water heater in the first place? Don’t water tank versions work well enough?

Perhaps, but water boilers without tanks offer some distinct advantages in more ways than one.

Energy Savings

Think about how a hot water tank works for a moment. In order to keep the gallons upon gallons of hot water hot, the gas has to activate frequently throughout the day whenever it sense the temperature has fallen below the desired heat setting, or if one simply uses a lot of hot water, be it for a bath, laundry, etc.

This constant on/off cycle uses up your gas, even when you aren’t actually using the water. Over time, that’s a lot of energy waste going on, and of course money being wasted too.

A tankless version only uses heat and energy when it’s activated, and then shuts off right after. There’s no meaningless heating of water throughout the day, simply to keep a giant tank of water hot enough just in case you decide to use hot water at any given moment.

Endless Hot Water

Ever run out of hot water in the middle of taking a shower? Your hot water tank was too depleted to keep supplying hot water, probably due to either someone else taking a long shower or bath before you, or doing a few loads of laundry during your bath.

When using a tank, you are always operating with a finite amount of water. These heaters heat as the water enters and comes to your fixture or appliance, so you never have to worry about running out. You could leave the shower on all day long, and you’d still never run out.

For some households with lots of kids or roommates, this is an invaluable advantage that can certainly help things go smoother in the mornings.

Avoids Catastrophic Messes

Most of us know someone that’s had a hot water tank fail at some point in life. More often than not, this leads to the tank leaking countless gallons of water into the home, ruining hardwood floors carpet, and more. It can be an event that ends up costing a homeowner thousands of dollars.

While proper care and maintenance can help avoid this, when you’re dealing with a huge tank of water sitting inside a closet or utility area, it’s always a risk.

Tankless hot water heaters don’t store water, so there’s nothing to spill or leak.

Improves Home Value

Tankless systems are environmentally friendly, and have a sort of modern allure that is appealing to many prospective buyers. Installing these water heaters in your home can instantly boost your home’s value, and make it appear more attractive to buyers.

Types of Tankless Hot Water Heaters

Natural Gas

A popular type for those going for a replacement that will have little to no drop-off from a hot water tank, natural gas tankless water heaters use the game gas lines your conventional tank heater uses.

The unit is installed into the gas line, often in the same hot water closet. The water is then fed into the unit, which triggers the ignition that lights the flame, which then heats the water as it passes through.

Natural gas units do require venting, which requires a lot of extra work beyond just installing the unit in the home. Vents can run horizontal or vertical, depending on your home.

Natural gas water heaters are usually the most powerful, provide seemingly instant hot water, and offer a higher flow rate of hot water. However, they are not as energy efficient as electric models.


Electric tankless hot water heaters are completely gas-less, and rely on electrical heating elements that heat the water as it moves through the unit.

Since these don’t require gas, they are easier to install, and also do not require any ventilation.

In terms of energy efficiency, electric water heaters are easily the best, and can offer the most savings on your bills. However, they are typically not as powerful as gas models, and may take a little longer to get the hot water flowing.


Propane tankless heaters operate just like natural gas models, but have the ability to hook up propane tanks instead of being slaves to gas lines. Some models are compatible with both natural gas lines and propane tanks.

Using propane allows the boiler unit to be installed anywhere, rather than where the gas connection is. Many portable models use propane, and also some smaller ones for homes with little water use.

Whole Home vs. Point-of-Use

One key difference to be aware of with tankless units is whole home and point-of-use versions.

As the name suggests, whole-home units operate like a tank heater, installed in the main location that equally serves all water lines in the home simultaneously.

Point-of-use units are meant to be installed into the water line of a particular fixture. This most often involves a sink but can be installed into a shower water line. These units supply hot water directly to that particular fixture, which usually makes them very efficient with a high flow rate.

Terms to Know

In order to comprehend some of the main words used in describing the features and specs of these tankless water heaters, here are some quick definitions to get familiar with.

Flow Rate

This refers to the amount of water a hot water boiler can provide, both maximum and minimum. This is measured in gallons per minute (GPM.) The maximum GPM is what the unit can put out in ideal conditions, while the minimum is the amount of water required to trigger the system into turning on and heating the water.

Inlet Water Temperature

Inlet water temperature is the temperature of the water coming into your home and inside the unit, prior to being heated. This has a significant effect on your flow rate, and the temperature range of your water as well.

Inlet water temperatures change throughout the year, depending on where you live. When the inlet water is colder, your hot water heater has to work harder to quickly convert the cold water to the desired temperature, which may reduce flow rate.

Temperature Rise

Sometimes when reading about a particular unit, you’ll see the information refer to what’s known as a temperature rise. This figure is the difference between what you have the water heater set at, and what the inlet water temperature is.

For example, if the inlet water temperature is 65 degrees, and you have your water heater set at 110 degrees, the temperature rise is 45 degrees. Manufacturers will often list what the flow rate is in relation to the temperature rise, such as: “3.5 GPM when there’s a temperature rise of 40 degrees.”

Larger temperature rises often result in lower flow rates.

What to Look For When Choosing a Tankless Hot Water Heater?

Thinking about buying a tankless water heater? Make sure you go over these aspects first.

Power Source

The power source of the unit will determine how well it works, and where you can install it in the first place.

Natural gas units will need to be patched in to your gas line, which is almost always where your water tank was prior. There are always exceptions to this, but also keep in mind that you’ll need to install ventilation as well.

Electric models can be installed practically anywhere, as long as there is a power outlet nearby.

Propane models can be installed most anywhere too, but they almost always need a power outlet for the ignitor, and usually require ventilation as well, but not always.

Gallons Per Minute/Flow Rate

This is incredibly important, as this indicates the overall level of performance you have available, which in turn determines how many water fixtures and/or appliances you can use in your home at the same time, without experiencing diminished water pressure or water temperature drops.

Here are some estimates for how much water you’ll use for each application:

  • One sink or shower – 1.5 GPM
  • One shower and one sink simultaneously – 4.0 GPM
  • Two showers simultaneously – 5.5 GPM
  • Some like to discuss GPM in relation to a home’s size, but this isn’t always accurate. The GPM is more in relation to how many water applications you can use at once.

So, if you have a larger family, and don’t want to have to worry about running a dishwasher while someone is showering, a GPM of 4+ is where you should be looking. If you live alone, or with one other person, you can often get by with a GPM below 3.

*Water-saving shower heads are a great way to get more out of your water heater, as they restrict flow while maximizing water pressure, enabling you to have higher water pressures while using less gallons per minute.

I recommend you purchase one of these shower heads for each shower in your home, regardless of your water heater’s GPM.

*Keep in mind that those living in colder climates will need a higher GPM to cover the temperature rise gap.


Tankless water heaters are always smaller than actual water tanks, but the size is still important if you are trying to get a good fit in the space you’ve chosen to install it. Larger heaters usually it where you previously housed the water tank, such as a closet or laundry room, but point-of-use models can be harder to fit when being placed behind a sink or shower.

Make sure you measure the space and compare it to the unit you’re considering before purchase.


As you can see, tankless hot water on demand heaters are really not all that complicated, you just need to know what to look for, and what your water needs are going to be. Hopefully you now have confidence with your buying decisions as well.

These 10 products all vary from each other in many ways, but the diversity I covered was intentional, making sure to touch on a wide range of different budgets, flow rates, heat sources, and size.

Make sure you double check the specs in relation to your home’s needs, and of course the space you’ll be installing the unit in. After ordering the best tankless water heater of your choice, and completing the installation, you can immediately get to enjoying an endless supply of hot water on demand, saving on energy costs in the process. Good luck!

Scroll to Top