Best Tankless Water Heaters (2021): In-Depth Reviews

If you’re already looking into tankless water heaters, you’ve probably heard about many of the benefits. You know these units will save you a significant amount of money on your utility bills over the long term -saving most buyers an average of 1/3 their fuel costs! You also know that they have the potential to provide unlimited, continuous hot water. They’re not limited by their tank size, which means you won’t have any limits on the amount of hot water you can access! If any of these benefits are new to you, you can read more on the pros and cons of tankless water heaters! To make a long story short, they’re one of the best investments a homeowner can make right now.

The downside of having such an exciting new product is that many companies jump on the bandwagon. Tankless water heaters are incredibly popular, and many companies have cranked out their own versions without taking the time to engineer or build them properly. That can make it hard to figure out which ones are actually worth your money. Plus, given their high price tags, the stakes are high for you to pick the right one for your home.

Well you’re in the right place! We’ve done the research, and have four tankless heaters to recommend, including best sellers, best value, and best for medium and high demand. We’ll help you figure out the best option for your specific needs, so you can spend your money wisely. Whether you live alone or in a big house with a lot of folks, one of these heaters will be the right one for you.

ModelProduct ImagePrizeRatingPriceMax. FlowrateSuitable House Size?Suitable Climate?
Rheem RTEX-13Best Seller4.1$4 GPMSmall Mild
EcoSmart ECO27electric tankless water heaterBest Value4.3$$6 GPMSmall - LargeCold - Mild
Rinnai V65iNBest Medium-Demand Heater4.5$$$6.5 GPMMediumCold
Rheem RTGH-95DVLNlow NOx water heaterBest High-Demand Heater4.4$$$9.5 GPMLarge Anywhere

Best Tankless Water Heater Reviews

1. Rheem RTEX 13 Electric Tankless Water Heater

Best Seller

popular heater

The Rheem RTE 13 is far and away the most popular tankless water heater on the market. The brand-new RTEX-13 is the updated version, and it’s even better! This model has only been out a short while, but it’s already proving to be a more reliable, user-friendly unit than the previous one.

The Rheem is an ideal choice for a one-shower household, or for two showers if they’re equipped with 1.5 GPM low flow showerheads. This one is a terrific choice if you live alone, and should similarly work well for couples/roommates in one bathroom apartments.


The obvious advantage for this Rheem water heater is the price, which is pretty unbeatable. As the reviewer noted above, it’s extremely small, which again would be an advantage for people living alone or in single-bathroom households. Since it is an electric heater, it will cost less upfront to install, and if it lasts even only a year and a half, it will pay for itself. Previous buyers reported that this one easily paid for itself in less than two years!

It has a maximum flow rate of up to 4 gallons per minute (GPM), which is very impressive at this price. Such a high flow rate means you can be taking a shower while someone in the next room washes their hands.

Even with such a high flow rate, it’s super compact and convenient, so you can install it in cabinetry, or hidden under the sink!

This latest version adds a user-friendly digital thermostat. It has a simple dial and very accurate temperature readout, accurate to within a degree.

At 99.8% efficient, you don’t get more intelligent design than this!

The older version wasn’t perfect in terms of reliability, especially when you compared it to the larger Rheem water heaters. This one gets back to the company’s reputation for spotless durability records. It has an improved copper heat exchanger and


The flipside of being a small unit means that it is not the most powerful. Without low flow showerheads, two simultaneous showers is out of the question, and given that the 4 GPM flow rate is a maximum, you shouldn’t expect to use dual 2.0 GPM fixtures at once.

The Rheem isn’t the best unit for larger households (more than, say, three people). We recommend it for apartments, or for single bathrooms in larger homes where it’s more convenient to add an additional tankless unit than to try and make distant suites run off a central heater.

Reviewers say that the flow rating might not live up to expectations in cold climates, especially in larger households. Most agreed that it’s not a unit for the coldest climates.


By far the cheapest unit here, with a large flow rate for the price, the RTEX 13 is a great choice for small households and apartments. It could also be made to work in larger households, as long as you are conscientious about hot water usage. Just don’t expect it to thrive if you push it to the limit (i.e., simultaneous showers, particularly cold climates). It’s probably worth taking the 4 GPM claim with a grain of salt, and it’s always good to err on the safe side with your flow rate requirements to ensure proper performance. With all that said, this unit is popular for a reason. It provides a lot of output for the price, and it’s very easy to make work from a space perspective.

2. Ecosmart ECO 27 Electric Tankless Water Heater

Best Value

electric tankless heater

The Ecosmart ECO 27 is one of Ecosmart’s most powerful heaters, designed to handle on-demand water heating in even the coldest climates. In warm climates it can run several fixtures at once in a larger household. This unit is ideal for the northern United States, where incoming water temperature can reach as low as 37°F. The ECO 27 is capable of heating nearly 3 gallons per minute at this low temperature. It can handle up to two showers running at the same time and never run out of hot water. For homes in the Southern United States, the ECO 27 is perfect for a high demand of hot water between multiple applications. In the South, it can run at 6 gallons per minute, which means you can run four showers and a sink simultaneously and never run out of hot water.


It excels in the cold. The ECO 27 is a heater that can hang tough in the cold of winter, possessing a 3 GPM flow rate even at 37-degree inlet water temps, which is just about as cold as you can get without your inlet pipes freezing.

That power comes in handy in warmer applications, too. The Eco 27 can provide up to 6 GPM with more temperate weather! That’s easily enough to run two showers at once, especially if you’re using low-flow fixtures.

It’s still relatively affordable. Plus, it’s more energy efficient than the Rheem. The ECO 27 self modulates to accurately use energy only when called to do so, which means increased efficiency and increased energy savings.

Best of all, it has a lifetime warranty on the unit itself. That’s as good as it gets for coverage. The warranty even transfers between owners, if you sell your house. Installing this unit will make it easier to sell your house, too, since it raises the market value! And the price is, comparatively, quite reasonable.


A couple of reviewers note that the effective water flow rate performed significantly below expectations, with colder water than they desired in cold climates. And, unless you live in a southern climate, the flow rate might not be high enough to ensure seamless, unlimited, piping hot water throughout a larger household (5+ people). It’s not quite as powerful as the Takagi we’ve recommended as the best of the best.

The lifetime warranty has a lot of fine print, and some reviewers were disappointed by the level of customer service they received when they ran into problems with their units.


With a reasonable price tag and the ability to power through colder temperatures, the ECO 27 could be a great mid-sized household option (3-5 people). The effective flow rate in the winter will be lower in cold climates, but you might be able to adjust to a slightly differentiated hot water schedule in the cold parts of the year, with increased performance the rest of the time.

This one is a good choice if you want a bit more power and flow than the Rheem RTEX 13 above, without spending a tremendous amount more.

3. Rinnai V65iN Indoor Tankless Water Heater – Natural Gas

Best Medium Demand Heater

The Rinnai is an extremely well-reviewed water heater that should be perfect for heating water for most households of up to 5 people, even in cold climates. If you have a house with a lot of people who need showers, this may be the best choice for you! It’s also a good choice for people who want to hook multiple showers up to the same unit.


This one is similar in energy usage to the ECO 27, but will be more reliable and allow slightly higher flow rates, in the winter/cold climates.

The Rinnai is extremely well-liked, with excellent reviews. Customers love how quiet it is, how efficient it is, and how low their gas bill becomes. Every part of a Rinnai Tankless water heater is replicable so components can be easily switched out.

3 showers at once also won’t be a problem for the Rinnai, especially for households with at least one low-flow showerhead. In warmer climates, it will be able to handle up to four showers at once.


It costs a lot more than the ECO 27. The Rinnai outperforms the ECO in colder climes, but in warmer climates they have similar flow rates, so medium-sized households (3-5 people) in warmer places may be able to get away with the cheaper option.

Since this is a a natural gas tankless water heater, significantly higher upfront costs are required to vent the gas to the outside. That’s why this costs a bit more to install than our cheaper recommendations, which are electric.


The Rinnai is a great mid-sized option if you are sure you want a gas heater and want to be assured of performance in cold and hot weather. But if you live in a warmer spot, you might be able to get away with the ECO 27 above and have a similar experience for less money. Having said that, the Rinnai is probably a more reliable choice for the long haul.

4. Rheem RTGH-95DVLN Direct Vent Tankless Natural Gas Water Heater

Best High-Demand Heater

low NOx water heater

This upgraded Rheem rtgh-95dvln 9 5 gpm is a real beast of residential tankless water heaters. Seriously, you can almost see the fur! Someone could take a two showers, run the dishwasher, hand wash a pan, and do a load of laundry on this unit–all at the same time! All its beastliness comes at a cost that may make it prohibitive for a lot of folks, but if you have a large demand for a supply of hot water, this is a great choice.


This Rheem is a condensing unit, which means it extracts the heat from exhaust gasses for increased energy efficiency––and increased savings for you! As a condensing natural gas heater, this Rheem unit will save you the most money in long-term energy costs in the long term, because gas is cheaper and it is extremely energy-efficient with an energy factor of Up to .96 EF.

It’s also surprisingly compact, given the power it’s capable of putting out.

And with a 9.5 GPM flow rate, you will never, ever run out of hot water, unless you arbitrarily try to push it to the limit for no reason.

Cold climates do not threaten to dim your hot water happiness in the slightest, as it comes with freeze protection up to -30 degrees Fahrenheit.

Its not a deal breaker but it also comes with a digital remote control.


This is by far the most expensive heater on this list, and gas tankless water heaters, have significant installation costs beyond just the list price. You’ll still recoup those costs over the long term, but the initial startup cost will probably be hard for some folks to handle.


Smaller households don’t need something this massive, but for the ultimate hot water peace of mind it’s hard to beat this unit. We recommend it to any large households with budgets that can make it work.

On-Demand Water Heater Buying Guide

To make an informed, considered choice of a tankless hot water heater, you need to think about a lot of variables: gas vs. electric, hot water demand, the climate you live in, installation costs, and of course, how much you have to pay. Not every household needs the big behemoth heater, and not every household can get away with the smaller one. There is a lot of technical information worth considering before your purchase.

Gas vs. Electric: This is probably the first decision you should make as you shop. Each option has its own advantages and drawbacks. A natural gas or propane tankless water heater is almost always going to be cheaper than electricity, so from a long-term utility perspective, gas heaters will save you more money. They’re also more powerful, and can work more quickly. That makes them the better choice for many larger households.

However, the big drawback to gas heaters is upfront cost––not only do the units themselves tend to cost a little more, but because the indoor models require venting, the install cost can also be significantly higher. Your exact household setup will determine the full scale of your startup costs, but the higher price point of gas units makes electric heaters the more popular choice on the market right now. On the other hand, folks who go the natural gas/propane route generally see better reliability over the long term.

Consider which option makes sense in your overall utilities scheme. If you already use a natural gas or propane line for heat or your current water heater, it probably makes sense to go that route. If you’re trying to become more environmentally-responsible and are planning to install solar panels, it could make sense to install an electric model. Everyone’s home and vision for their living space is different, so think about how your new tankless water heater will fit into the big picture.

Hot Water Demand: Tankless hot water heaters list a maximum flow rate in gallons per minute (GPM), which is the maximum volume they can heat effectively. Showers have the highest flow rates of any appliance––high-flow showers vary from between 2.5-3 GPM, and low-flow showerheads tend to give out around 1.5 GPM. So, most of us judge a unit in terms of how many showers it can power at one time.

It’s not just a matter of counting showers, though. You might want to have multiple hot water appliances running at once. If so, you will probably want to think about a larger unit with a larger capacity. The smaller units tend to have a much lower GPM, and could certainly be made to work if you can adjust to doing nothing else hot water-related while someone is in the shower. For instance, if you time laundry cycles for your washing machine around showers, you probably don’t need a large-scale hot water heater. If you don’t want to think about hot water management, go for a more powerful model with a higher output capacity.

Climate: In the United States, northern climates have significantly lower inlet water temperatures than other parts of the country. To deal with that, you should round up, and buy a unit with a higher flow rates than you think you need. That gives you a nice margin of error to ensure effectiveness during the coldest months. People in southern climates can get away with smaller units closer to actual usage requirements, because they have to work significantly less hard to increase temperature rise. Remember: while you may have to pay more up front for a machine that can handle your colder weather, homeowners in northern climates also benefit the most from the energy savings from tank water heaters, because it’s much more expensive to heat water in cold climates year-round in the first place.

Installation Costs: Please be advised that while gas heaters tend to be more expensive to install, both types have significant installation costs associated with them. The exact amount it will cost to install your unit varies widely depending on your exact situation, but will probably cost at least $300 or more.

If you’re feeling up to it, you can install your water heater on your own but be sure to follow the instructions properly. You can watch this video as a guide to make it more easy to install but more importantly, follow your own manual.

Many of the negative reviews online reflect complaints about the warranty––we strongly recommend reading the fine print and hiring licensed technicians to make sure you qualify, unless you are a DIY fanatic who’s willing to forgo warranty coverage.

Conclusion: What’s the Best Instant Water Heater for You?

We hope this list has helped you narrow down the type of water heater you are looking for, or even pointed you to a model that suits your specific needs. Your success with any of these options will depend on the needs of the individual household, and is a matter of balancing lots of different specs and factors, as we’ve discussed.

Many people choose the Rheem RTEX 13 (option #1) because of low upfront costs, and for smaller households (1-2 people) it is a terrific option.

The ECO 27 (option #2) and the Rinnai V65iN (option #3) are both good choices for medium-demand households (3-5 people). The ECO 27 is best for medium-demand folks on a budget, while the Rinnai offers more consistent performance and better long-term reliability.

And if you want to be assured of hot water in your heart of hearts, no matter the circumstances, the Rheem RTGH-95 (option #4) bulldozes the competition. However, it’s pretty pricey, and most households probably don’t need a high-demand unit like this.

See other products and read our reviews for:

Best Electric Tankless Water Heater

Best Gas Tankless Water Heater

Best Water Heaters for RVs

Most Luxurious Showerheads


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