Table of Contents
- Best Tankless Water Heaters
- Tankless water heater buyer’s guide
- What is a tankless water heater?
- Types of tankless hot water heaters
- How does a tankless water heater work?
- Things to consider when buying a tankless water heater
- How to size a tankless water heater?
- Tankless water heater cost
- Pros/Cons of tankless water heaters
- Tankless water heater installation and maintenance
- How to maintain your tankless water heater
- Frequently Asked Questions
Ever had to bathe in a half-full bathtub because the hot water ran out? It’s a struggle that seems pretty old-fashioned nowadays – and that’s because it is. By 2018, the tankless water heater market was valued at $2.8 billion globally, with millions of people allured by their on-demand water production, energy efficiency and space-saving benefits.
When searching for a tankless water heater, it’s important to make the smartest buying decision for your requirements.
I’m here to help you do that.
With more than a decade of experience in the water treatment industry, I’ve written for a number of key publications, including WQP Magazine, HowStuffWorks, and Simply Recipes. My website now has a yearly readership of nearly 1 million people, and I know the importance of only recommending products that truly live up to the hype.
I’ve ranked the best tankless water heaters in this guide based on factors including performance, ease of installation, durability, customer satisfaction, and customer support from the manufacturers. Though there are many more tankless water heaters on the market, I’ve focused on the cream of the crop – those that are the best available right now.
I’ve split this guide into two sections:
- A reviews section, which features 10 of the best tankless water heaters in 2021
- A buyers’ guide, which discusses costs, sizing, installation, maintenance, and other things you’ll need to know when buying a tankless water heater
Best Tankless Water Heaters
- EcoSmart ECO 27 (Electric)
- Stiebel Eltron Tempra 24 Plus (Electric)
- Rheem RTE 13 (Electric)
- Rinnai RUC98iN Ultra Series (Gas)
- Takagi T-H3-DV-N (Gas)
- Eccotemp FVI-12 (Gas)
- Rheem RTGH-95DVLN (Gas)
- EcoSmart ECO 11 (Electric)
- Thermoflow Elex 18 (Electric)
- ECOTOUCH ECO55 (Electric)
|EcoSmart ECO 27||Power Type: Electric|
Flow Rate (GPM): 6.5
|Stiebel Eltron Tempra 24 Plus||Power Type: Electric|
Flow Rate (GPM): 4.3
|Rheem RTE 13||Power Type: Electric|
Flow Rate (GPM): 4
|Rinnai RUC98iN Ultra Series||Power Type: Gas|
Flow Rate (GPM): 9.8
|Takagi T-H3-DV-N||Power Type: Gas|
Flow Rate (GPM): 10
|Eccotemp FVI-12||Power Type: Gas|
Flow Rate (GPM): 3.5
|Rheem RTGH-95DVLN||Power Type: Gas|
Flow Rate (GPM): 9.5
|EcoSmart ECO 11||Power Type: Electric|
Flow Rate (GPM): 2
|Thermoflow Elex 18||Power Type: Electric|
Flow Rate (GPM): 2.7
|ECOTOUCH ECO55||Power Type: Electric|
Flow Rate (GPM): 1.2
Tankless water heater buyer’s guide
We know what a big decision it can be deciding to install a tankless hot water heater in your home or not. Not only that, but the hours of research it takes to find the perfect product for your individual needs.
That’s why we created the following buyer’s guide where we have compiled the most up to date, relevent and helpful information so that you can learn everything there is to know about tankless water heaters, and how to find the ideal system.
Let’s jump in!
What is a tankless water heater?
Tankless water heaters, also known as instant or on-demand water heaters, are water heaters that heat water immediately as it flows through the system. They don’t hold water in a tank, hence the name “tankless”. Instead, when you turn on your hot faucet, the best tankless water heater can produce warm water within seconds.
Types of tankless hot water heaters
There are two types of tankless hot water heater to be aware of: gas water heater and electric water heater.
Electric tankless water heaters use an electric element to heat water. They tend to be cheaper to buy upfront, costing between $500 and $800. They are usually half the size of a gas tankless water heater, and they don’t need ventilation, so they’re suitable for storing in smaller spaces.
They require less maintenance than gas alternatives, and troubleshooting a problem is usually easier, as the system is less complex than a gas one. However, you may need a high amount of power to run an electric tankless water heater, especially if you live in a place that experiences colder climates in the winter.
These water heaters also tend to produce a lower flow capacity, and if your home has a power outage, you’ll be left without hot water.
Gas tankless water heaters use a burner to heat water. They generally have a higher capacity than electric alternatives, and can provide you with a higher GPM of hot water.
While gas heaters are more expensive to buy upfront, their running costs tend to be lower, which makes a bigger investment worth it in a relatively short space of time. They can also be used in homes with no power.
Installation of a gas heater is more complex than for an electric heater; more space is needed, and ventilation is a must.
This means that the installation process is costlier if you’re hiring an expert (which you definitely should) to carry out the job. Tankless gas heaters also pose a higher risk than electric heaters, because they could leak gas or carbon monoxide into your home.
Finally, tankless gas heaters require more yearly maintenance compared to electric heaters – but making that extra effort can help you to enjoy a more efficient system in the long run.
How does a tankless water heater work?
Understanding exactly how a tankless water heater works is not as complex as it seems. There’s no major science behind the process to put you off investing in a system, and this guide will provide you with the knowledge you need to confidently purchase a heater yourself.
The novelty of a tankless water heater is that it can heat water directly without needing to hold it in a tank. This means that the water that flows straight into your home’s pipes passes through the heater when you switch your hot faucet on, and is heated immediately, before continuing its journey to the faucet.
Let’s look first at how electric tankless water heaters work.
When you switch on your hot faucet, a flow sensor detects this action and prompts the heater to kick into action. In this case, electric elements are used to rapidly heat the water. Imagine the elements to be a bit like the ones in an electric stove – they can quickly reach a high heat, which they can continue to produce until the flow sensor detects that you have switched the hot faucet off.
Gas tankless water heaters work on a very similar level.
They also have a flow sensor, which detects when the hot faucet is being used, and triggers the burners in the system to get to work. These burners are more powerful than electric elements, and can produce hot water at a faster rate. When the faucet is turned off, the burners will go out, preventing any more water from being heated.
Things to consider when buying a tankless water heater
Buying a tankless water heater takes some responsibility. It’s a bad idea to make a purchase without understanding exactly what you need to look out for in a good product. You’ll need to make the following considerations when looking for a tankless water heater for your home:
Not all tankless water heaters provide the same flow rate of water to your home. The higher the flow rate, the more water-based appliances you will be able to use at the same time – so, for example, a high flow rate would allow you to shower, wash the dishes, and run a dishwasher and washing machine without lags in hot water production.
A low flow rate would result in one or more of these appliances running cold water, as the tankless water heater simply wouldn’t be able to keep up with the hot water demand.
There is no “good” flow rate for a tankless water heater, as it depends on your personal hot water usage in your home. If you were to only shower and run one water-based appliance at the same time, for example, paying more for a high flow rate would be pretty unnecessary.
Flow rates range from 5 to 11 GPM (or gallons per minute), with tankless water heaters generally offering a higher GPM than electric.
Energy Factor (EF)
All tankless water heaters have an Energy Factor (EF) that denotes their efficiency in converting energy during use.
According to Energy Star, electric tankless water heaters have Energy Factors that range from 0.96 to 0.99, while gas heaters need to meet an Energy Factor requirement of .062 for efficiency (though the best gas tankless water heaters have an Energy Factor of up to the mid 80s).
You should be able to find a product’s EF in the description of the heater; contact the manufacturer if you can’t.
Electric tankless water heaters are very energy efficient, using up to 98% of its energy to heat water.
Gas tankless water heaters are still considered efficient, but use up to 85% of the supplied energy to produce hot water. Still, because gas water heaters can heat up water at a faster rate and at a higher GPM, you will usually save money in the long term.
The efficiency of a tankless water heater largely depends on the time it takes to raise water temperature.
The best tankless water heater can raise water temperature from around 40 to 50 degrees to around 100 to 110 degrees (the average temperature of a shower) in a matter of seconds.
Tankless water heaters with a little less power will take longer to produce hot water, or may not be able to produce water at your desired temperature at the rate of the water flowing through the system.
The speed of temperature rise in a tankless water heater will be more important to you if you run multiple appliances at a time, which rely on hot or boiling water to run.
For some people, fuel type may not be too important when it comes to purchasing a tankless water heater. But there may be positives and negatives to gas or electric options that sway your opinion either way.
For example, if you’re particularly safety conscious, you may want to avoid gas water heaters, which pose a very small (but still possible) risk of explosions and carbon monoxide poisoning.
Fuel type could also come down to convenience – for example, if you already have the means set up for installing an electric tankless water heater, you may want to save the fuss and hassle of installing gas lines for a gas alternative.
Price may also play a factor in your decision, as even though gas tankless water heaters are cheaper in the long run, their upfront investment is too much for some budgets.
Size of system
The size of a tankless water heater may be a deal-breaker for you, especially if you’re short on space. Gas water heaters take up more room, and need to be installed in an area where proper ventilation can be achieved. Even a smaller capacity gas water heater will take up more room than a larger electric water heater because of its necessary add-ons.
Generally, standard sized electric tankless water heaters tend to be around 7 inches wide and 10 inches high, while gas alternatives are at least 20 inches wide and 30 inches in height.
How to size a tankless water heater?
The size of a tankless hot water heater doesn’t just determine how much space it’ll take up. Size is also linked to a heater’s capabilities, including flow rate and temperature rise.
Determining flow rate
The first thing to consider is what flow rate you are looking for in your home. To do this, you need to look at how many water-based appliances you run, and consider that there may be occasions when these are all running concurrently.
Take a minute to look through your user manuals for these appliances and determine their flow rates, if you don’t know them already.
You can then add up these flow rates to produce an estimated hot water flow rate that you will need your tankless heater to produce in order to provide enough hot water for all appliances at the same time.
For example, let’s say your shower has a flow rate of 2.1 gallons per minute, the average GPM for a shower in the US. Maybe your washing machine has a flow rate of 2.0 gallons per minute, and your dishwasher and your kitchen faucet have a flow rate of 1.5 gallons per minute each.
This means that your tankless water heater’s flow rate needs to be at least 7.1 GPM to be able to accommodate for all your appliances at the same time.
2.1 + 2.0 + 1.5 + 1.5 = 7.1
The general rule is that the larger the heater, the more heating elements or burners it will have, or the greater surface area these heating elements or burners will cover. In this sense, a larger tankless water heater usually produces water at a higher GPM.
Determining temperature rise
Your next step is to determine your temperature rise.
Again, look at the temperatures your appliances need to run at (or, in the case of showers and faucets, your desired temperatures).
Then subtract the incoming water temperature – that’s the temperature of the water flowing into your home – by the output temperature you require based on the appliances in your home.
If you live in a place that sees colder climates in the winter months, you’ll want to look for a larger tankless water heater, which will be able to heat your colder incoming water up to a high temperature in the fastest time possible.
Water heaters should specify their temperature rise in their product description, and temperature rises can vary from 50 to 70 degrees, sometimes slightly lower or higher than this.
Tankless water heater cost
People often ask “how much is a tankless water heater?” when beginning their research.
Whether you buy gas or electric, tankless water heaters are a big investment.
You’ll need to pay $500 minimum upfront cost for something with decent capabilities, but it may be worth saving up for something that costs at least $800 to $1,000 for better performance if you have a larger home with more water-based appliances.
Many people forget to factor in the cost of installation, which also needs to be paid for upfront. In many cases, installation of a tankless water heater can actually cost more than the heater itself.
Tankless gas water heaters cost the most to install, at an average of $1,000 to $1,500 for whole house models.
Electric water heaters cost slightly less, at around $700 to $1,000 on average. Unfortunately, there’s no getting out of parting with a substantial amount of money for installation, as the risks of paying less for someone to do a cheap job just aren’t worth it.
|Water Heater Fuel Type||Average Installation Cost|
|Gas||$1,000 – $1,500|
|Electric||$700 – $1,000|
Both gas and electric tankless water heaters will require flushing to remove any sediment or scale that may have built up in the system.
Luckily, this can cost nothing, and you can safely do it yourself without a professional.
With that said, after years of running, it’s pretty likely that your tankless water heater will come across one of several issues that require a professional examination and repair. Most plumbers charge between $50 to $150 per hour, so if you’ve got a big issue at hand, repairs might not come cheap.
Pros/Cons of tankless water heaters
In many cases, the pros of tankless water heaters largely outweigh the cons, but it’s important to be aware of the positives and negatives of using this type of heater in your home before you make a purchase.
- Instant hot water
With tankless water heaters, there’s no waiting around for hot water to be produced. As soon as you turn on your faucet, the heater kicks into action, producing hot water in seconds. This is far more convenient for you – after all, no-one wants to wait five minutes for hot water when they just want to wash their hands after using the toilet.
- Longer lifespan
The best tankless water heaters typically last for twice the amount of time of a traditional water heater with a tank. You can expect at least 20 years of use out of a tankless water heater, so if you’re looking for a product that won’t need replacing as quickly, tankless water heaters are a great option.
- More efficiency
While tankless water heaters are more expensive than traditional water heaters with a tank to purchase upfront, they have been found to be up to 30% more efficient than the alternative. This will help you to save money on a monthly basis, which really adds up annually.
- Saves space
Whether you buy a larger gas tankless water heater or a smaller electric system, you will still save space when compared to a bulky water heater with a tank. You can quite simply install a tankless water heater on the wall in an inconspicuous location, like your basement or washroom. Just remember to factor in for ventilation if you’re installing a gas tankless water heater.
- No repeated water heating
A big issue with standard water heaters is that they often repeatedly heat the same tankful of water whenever a hot water faucet is switched on. This produces something called “standby loss”, which refers to the energy that is lost from the water heater firing up to reheat the water on multiple occasions. As tankless water heaters only heat water that flows straight through the system, they completely eliminate standby loss.
- Never run out of hot water
Another issue with water heaters with a tank is that they run out of hot water when the tank has emptied, and you will then need to wait for an entire tank of cold water to be heated before you can access hot water again. With tankless water heaters, heating is instant, so you never technically “run out” of hot water – it’s always readily available.
- Low or inconsistent temperatures
If you have multiple appliances on the go at once, there’s a chance that even the best tankless hot water heater will struggle to keep up with demand. This may mean that when you come to take a shower, the water isn’t quite hot enough for your tastes, or temperatures are inconsistent.
- Cost more initially
Like many of the best investments for your home, you will need to pay more upfront for a tankless water heater than you will for a heater with a tank. This investment pays itself off in the long run, but if your initial budget is lower, the cost may hit you quite hard.
- May require additional equipment
When paying for a tankless water heater, you should keep in mind that you may need to factor in for additional equipment for installation. This especially applies to gas tankless water heaters, which require appropriate ventilation. You may need to pay to add features to the room you plan to store your heater in to make it appropriate.
- May take years for investment to pay off
You won’t see the financial benefits of a tankless water heater straight away. In the majority of cases, it will take several years before you start to “earn back” from the savings you’re able to make with an energy-saving tankless water heater. Of course, it’s worth it in the end, but it’s not the case that tankless water heaters aren’t miracle appliances that can help you save thousands of dollars a month.
- Not as effective for larger homes
There’s no denying that tankless water heaters are ideal for smaller homes with only a couple of water-based appliances. Larger homes with big families and lots of appliances will need to fork out for one of the most capable tankless water heaters if they want their heater to keep up with their family’s water usage. This will need parting with significantly more cash, and it still doesn’t guarantee perfect operation.
Tankless water heater installation and maintenance
In nearly all cases, it’s recommended that you call a professional to install your tankless water heater. This is especially the case for installing gas water heaters, which can pose a serious safety risk if they’re installed wrong. But if you have the skill and plumbing experience behind you, you could certainly save a buck or two by installing your tankless water heater yourself.
Here’s what you need to know about installation.
How to install
The majority of professional plumbers will offer installation of tankless water heaters as part of their service. Installation can cost anything between $1,000 and $5,000, depending on the job that actually needs to be done (i.e. is ventilation and gas line re-routing needed?).
A plumbing expert can take roughly 2 hours to install an electric tankless water heater, while gas heaters with additional fitting requirements can take 7 to 8 hours to complete. Many plumbers charge hourly rates, so keep in mind that installation of a gas tankless water heater will cost more for this reason.
Arranging for professional installation takes the responsibility of installation off your hands. If you’re not an expert plumber yourself, installing a tankless water heater is a very daunting task. If something was to go wrong, you’d only have yourself to blame. Hiring an expert means the company will follow up on any issues should they crop up after the unit has been installed.
If you’re appropriately skilled to install your tankless water heater yourself, we’ve provided basic instructions that generally apply to both gas and electric units. It’s difficult to write too specifically on installation, as the exact process largely depends on the product you’re installing and space available. Make sure to follow your included instructions carefully, and look for video guides for extra assistance.
You will need:
- A diverse toolkit
- A wall bracket for mounting the heater
- A means of ventilation (for gas heaters)
- A tape measure
- Plumber’s tape
What to do:
- Choose a location
If you haven’t already, choose a location for your tankless water heater. Consider a location with space for installation, with appropriate ventilation and nearby gas lines for gas tankless heaters. Many people prefer to store their tankless water heaters out of the way, which is possible to do in most homes.
- Prepare for installation
You need to mount your water heater vertically on the wall, and the power and water supply connections are usually found at the bottom. Your own heater may be slightly different from a standard appliance, so follow your manufacturer’s instructions carefully.
- Mount the heater to your wall
Most tankless water heaters will come with a bracket for mounting them to the wall. Screw this into place before installing your appliance according to the manufacturer’s instructions.
- Connect heater to supply pipes
When your heater is securely mounted on your wall, connect the inlet and outlet pipes to your water supply. This exact process varies from heater to heater, so be sure to follow advice in your product manual.
- Install shut-off valves
Next, install your shut-off valves at the inlet and outlet water pipes to allow you to switch off the water for maintenance. You may also need to install a pressure-relief valve.
- Open water valves
Open your water valves, but don’t switch on your gas or electricity just yet. Switch on the faucets in your home and allow water to run through. Check that everything looks as it should.
- Clean filter
Take your inline filter out of your tankless water heater and follow the manufacturer’s instructions for cleaning out any debris. Then slot it back into place inside the heater.
- Turn on the gas or electricity
Now it’s time to test your system out. Turn on the gas or electricity and run your hot faucet. If the unit doesn’t seem to be operating properly, consult your user manual.
How to maintain your tankless water heater
Over time, both gas and electric tankless water heaters can accumulate minerals and deposits that can damage the inside of their chambers. It’s your job to flush these minerals to ensure your system continues to work effectively for many years.
Here’s a step-by-step on how to maintain your tankless water heater:
Part 1: Flushing the System
You will need:
- 2.5 gallons of white vinegar
- A bucket
- Hosing lines
What to do:
- Turn off your power source
Start by switching off either your gas or electricity so that you can safely access your unit.
- Turn off your water valves
To prevent water from flowing through your system while you’re carrying out your maintenance, switch off your 2 water valves.
- Open your pressure valve
If you have a pressure valve, open it now to prevent a build-up of pressure inside your unit.
- Attach your hosing lines
Your tankless water heater most likely came with its own hosing lines for this very purpose. If you didn’t receive any with your heater, they’re easily found at most home improvement stores. You may need to look in your user manual for the exact instructions on how to attach the hosing line to your heater.
- Use 2.5 gallons (approx) white vinegar for cleaning
Undiluted white vinegar is the best choice for cleaning out your tankless water heater. It’s wise to avoid harsh cleaning chemicals, which could linger on the inside of the system and leach into your water. Vinegar has an acidic nature, and can dissolve mineral deposits and dirt without the need for anything stronger.
- Flush your system
Next, follow your manufacturer’s specific instructions on flushing your system to rid it of deposits. It will take between 30 and 45 minutes if you do the job properly.
- Remove your hosing lines
When the job is finished, remove your hosing lines and give them a rinse through with water. Close your valves and put your hosing lines in a safe place for future use.
- Restart your heater
Your user manual may say something about how to safely start your heater after flushing, so be sure to check in there before turning your heater back on.
- Test out your water
Turn on one of your hot water valves very slowly, allowing any leftover air to pass out of the pipe. The faucet may “sputter” for a couple of minutes as the air leaves – leave it on until the water is running freely as normal. If there is a problem, you may need to retrace your previous steps to ensure you have followed the manufacturer’s instructions correctly.
Part 2: Cleaning the Inline Filter
The majority of tankless water heaters nowadays have an inline filter that prevents larger sediment from being able to pass into the system and get trapped. You’ll find this filter somewhere along the unit’s water intake line – you might want to read your manufacturer’s instructions to find out exactly where it’s located.
You will need:
- A bucket
- Roughly 1 gallon of white vinegar
To clean the filter, here’s all you have to do:
- Switch off your water supply
Turn off your water supply to prevent leaking while you’re dealing with the filter.
- Remove the filter
It should be very easy to remove your filter from the line.
- Clean the filter
Add your white vinegar to a bucket and clean your filter in this vinegar solution. Make sure the sediment comes away from the filter and that any blockages are removed.
- Replace your filter
Put the filter back onto the line, using the opposite approach to how you took it off. Note that if your filter is looking old, worn or damaged, you may need a replacement one. Your filter might last for 6 months; or it might last for up to 3 years. You should find more information in your user manual.
Frequently Asked Questions
Can I use a tankless water heater if I have hard water?
Yes – and actually, tankless water heaters tend to be less affected by hard water as they don’t ever store water inside the system. This means there won’t be such a fast accumulation of scale and hard water deposits inside the system, though you still do need to flush it to keep it working at its best.
Do I have to buy a tankless water heater for my whole home?
No, you can buy point of use heaters that you can use for a single sink, shower or other appliance if that suits you best. These are a lot more wallet-friendly, though it doesn’t always make sense to invest in something that won’t benefit your whole home.
Why do I have to wait a second or two for hot water to come out of my faucet?
This is usually the case if your heater is far away from the faucet in question. You’ll simply need to wait for the water to run through the heater, then through your pipes and out of your faucet. You should only have to wait a couple of seconds, and the water should be consistently hot once it arrives.
Do I need to flush my tankless water heater even if I have a whole-home water softener?
Yes, it’s recommended that you flush your heater no matter what, even if you have a water softener. Failing to maintain your heater may shorten its lifespan, so it’s important to follow your manufacturer’s maintenance recommendations as closely as you can.
Can I reuse the white vinegar I have used for flushing my heater?
No, as the vinegar won’t be “pure” or clean anymore – it’ll contain the minerals and deposits it has picked up from the job. It’s important to use clean, fresh vinegar every time you flush your system.
How exactly does a tankless water heater help you to save money?
Tankless water heaters only produce hot water when you need it. In comparison, heaters with hot water tanks store water that might not even be used in a day. This wastes energy heating up the water for longer periods of time until it’s used.
How many tankless water heaters do I need for my whole home?
Providing you find a system with a good capacity, you should only need one. Look for one that has a high water flow if you frequently have multiple showers and water-based appliances running at the same time. There’s usually never a need to have more than a single tankless water heater for your whole home.
Will my heater be affected if I live in a place with a high altitude?
In some cases, yes. Gas heaters can’t work as efficiently in areas with altitudes of more than 4,000 feet. They are designed to work at sea level, so you would need to put more work into modifying a gas appliance to make it high altitude-friendly if you chose to go with one. Electric units, on the other hand, aren’t affected by altitude, so you’ll be much wiser to purchase an electric model if you live in a high altitude area.
How can I control the temperature of my water?
You can do this in one of two ways: at your faucet/ showerhead or at the unit itself. Most people now have a hot/cold faucet that can be adjusted to get the ideal temperature, and the same goes for shower units. If you have a separate hot faucet that gets too hot to use, or you want to adjust water for your washing machine or other appliances, you can manually adjust it at the tankless water heater’s control system.
Can I use existing venting for my unit?
9 times out of 10, no. You will normally be required to replace your old heater’s venting with venting that is suitable for the gas tankless heater that you’re installing. The manufacturer and/or installer of your tankless water heater may want to approve your venting before getting started with installation.
Are tankless water heaters worth it?
If you live alone, not always. But if you have a family of more than 2 people, absolutely. The money you save in the long run makes that initial investment more than worth it. Tankless water heaters can help you save up to $100 a year, and they have a much longer lifespan than water heaters with a tank. They also save a lot of space, and you won’t need to figure out a location for storing a whole tank.