Buying guide for best tankless water heater
Everyone has experienced the hassle of running out of hot water in the middle of a shower or filling the bathtub only to realize the water is cold because you washed dishes 15 minutes ago. These problems are associated with traditional water heaters, which keep a limited supply of hot water at the ready and take a lot of time to replenish, should the hot water be used up.
Thankfully, tankless hot water heaters offer a solution. These appliances are a fraction of the size of traditional heaters and cycle water through heating elements to provide a limitless supply of hot water at the temperature of your choice. Switching to a tankless heater is a great way to modernize your home and enjoy hot water for extended periods.
Our best pick is the Rinnai RU199iN Condensing Tankless Hot Water Heater. It is Energy Star–qualified and able to provide hot water to several appliances at once.
Expert tip
The use of water softeners is suggested with tankless systems to reduce mineral buildup that can limit flow to the heat exchanger.
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Which tankless water heater is best for your home?
Rinnai RU199iN Condensing Tankless Hot Water Heater
Best of the Best
Product Specifications
Voltage: 120V | Minimum Flow to Activate Unit: 7 gpm | Water Connections: 2 to 7 | Output Temperature Range: 98 to 140 degrees | Dimensions: 22.05” W x 14.76” D x 33.86” H
When it comes to water heaters, the popular brand Rinnai, which was founded in Japan in 1920, doesn’t disappoint. This indoor tankless water heater is compact and provides a powerful, high-pressure supply of hot water that can service up to seven appliances at once.
Energy Star–qualified, this unit runs efficiently and helps you save on energy costs. A 15-year manufacturer’s warranty on the heat exchange speaks to this heater's durability, reliability and quality construction.
For those who want additional features, such as app control and accessories that offer an even more immediate supply of hot water, this heater is compatible with several other Rinnai components.
EcoSmart ECO 27 Tankless Water Heater
Best Value
Product Specifications
Voltage: 240V | Minimum Flow to Activate Unit: 2 gpm | Water Connections: 1 to 2 | Output Temperature Range: Up to 120 degrees | Dimensions: 17” W x 3.75” D x 17” H
The small size of this heater makes it great for installing in tight spaces, and a digital LED control panel gives you precise, to-the-degree temperature control. Its self-modulating flow sensor regulates how much energy it uses to heat its water output, resulting in high-efficiency operation.
Able to provide up to 6.5 gallons per minute (gpm), this low-priced heater is an excellent option for anyone wanting to upgrade their quality of life with endless hot water at an affordable price. Users are satisfied with its performance and build quality.
Rheem RETEX-27 Performance Tankless Electric 24-27kw Tankless Electric Water Heater
Best Electric Option
Product Specifications
Voltage: 240V | Minimum Flow to Activate Unit: 0.3 gpm | Water Connections: NA | Output Temperature Range: 80 to 140 degrees | Dimensions: 17” W x 3.75” D x 17” H
Running at 99.8% energy efficiency, this electric water heater offers a great way to have hot water whenever you need it and save money at the same time. An external controller lets you fine-tune the heater’s temperature in single-degree increments for precise adjustments. Three heating chambers ensure that your hot water never runs out.
Users upgrading from traditional water heaters are amazed at the performance of this unit and its ability to provide hot water across several different appliances without issue. They also appreciate how easy it is to install and Rheem’s outstanding customer service.
Stiebel Eltron Tempra 24 Plus Tankless Water Heater
Most Precise
Product Specifications
Voltage: 240V | Minimum Flow to Activate Unit: 3.8 gpm | Water Connections: 1 to 3 | Output Temperature Range: 68 to 140 degrees | Dimensions: 16.63” W x 4.63” D x 14.5” H
This tankless water heater features Stiebel’s patented Advanced Flow Control, which reduces flow if hot water demands exceed capacity. This ensures that your water never goes cold in the middle of a shower. A backlit digital LCD shows you the temperature output, and you can make fine adjustments with its single-knob control panel. A savings monitor calculates your energy savings.
Buyers are impressed with the performance of this small unit, with some even turning on multiple showers at the same time to successfully test its ability to maintain hot water. The heater is protected by a seven-year warranty against leakage and a three-year warranty on parts.
Rinnai V53DeP Propane Tankless Hot Water Heater
Best Outdoor Option
Product Specifications
Voltage: 120V | Minimum Flow to Activate Unit: 3 gpm | Water Connections: 1 to 4 | Output Temperature Range: 115 to 140 degrees | Dimensions: 14” W x 7.9” D x 19.8” H
Ruggedly built for outdoor installation, this tankless water heater puts out hot water at 5.3 gpm and can provide endless hot water for up to four appliances at once. An optional module can be installed that allows you to control and monitor your heater via Wi-Fi. It runs on propane or natural gas and comes with a generous manufacturer’s warranty that covers its heat exchanger for 10 years.
Buyers appreciate this heater’s performance and regularly compliment its tight, well-made components and fittings. Because it requires a gas connection, professional installation is highly recommended.
Expert tip
Ensuring that any exhaust pipes from gas-powered units are clear of any obstructions - such as rodents, snow drifts, or animal nests - is imperative. If vent pipes are not clear, dangerous gasses can be trapped in the home
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How does a tankless water heater work?
Tankless water heaters only heat water when you need it, so minimal energy is wasted.
The beauty of a tankless water heater is its ability to provide a continuous supply of hot water. Compared to a traditional water heater, a tankless option is more efficient in its delivery and is a big energy saver. A tankless water heater is a heating element (gas or electric) that connects directly to the home’s water pipes. When a hot water tap is turned on, water flows through the element and on to its destination.
Electric heating elements provide a slower flow rate than gas-powered models. A sensor in the heating element turns on the burner, and as water enters the unit, a thermostat springs into action to quickly get the water to the desired temperature.
Gas-driven tankless water heaters need to ventilate through the ceiling and outside the house. Larger tankless systems, called gas-condensing units, are armed with a second heating system. These provide more hot water to homes where the occupants might want to simultaneously use a dishwasher, shower and kitchen sink.
Tankless water heater considerations
The most important consideration when it comes to choosing the right tankless water heater for you is how you’ll power it. If you don’t have a gas line available, you’re limited to electric heaters unless you decide to have a gas line installed.
Cost
Electric heaters will save you money in the long term thanks to their high-efficiency operation, but the high cost of purchase and installation could eat up those savings, depending on how long you plan to live in the home.
Some homes aren’t equipped with the necessary gas or electric connections required for a tankless heater, and having those systems professionally installed could come with a price tag in the thousands of dollars.
Efficiency
Gas models are easily more efficient than traditional tank-based units. However, their efficiency peaks somewhere near 85%, while electric models are more than 90% efficient.
Even though the fuel is generally less expensive than electric energy, many people choose electric models because they last longer and are cheaper to install.
Installation
When installing a gas-powered tankless water heater, new vents and ducts must be put in place to ventilate the byproducts of burning gas. If placed in a tight space, installation can be more rigorous due to the need for alternative venting, such as side-wall venting.
Electric models are often smaller and, as such, can be placed in smaller spaces where a gas tankless heater might not fit. An electric unit can be placed closer to the area where hot water is needed, adding to the efficiency and customer satisfaction. The only additional cost for an electrical tankless unit would be if a house’s electric service would need to be updated or remodeled.
Flow rate
It’s important to buy a tankless water heater with the capacity to meet your simultaneous hot-water demands. A small model won’t be able to supply a clothes washer, shower and kitchen sink at the same time. Before you purchase, try to anticipate scenarios where multiple appliances would need hot water at the same time. Check manufacturer ratings and customer reviews to determine whether the model you’re considering would provide enough water during your high-demand times.
Indoor vs. outdoor
No convenient space inside the house for a tankless water heater? Conveniently, some models are designed to be mounted on the outside of the house.
Mounting a heater outside requires additional consideration, however. If you live in a climate where temperatures dive below freezing, you need to take special maintenance measures so frozen pipes don’t damage your appliance. Notably, without Wi-Fi controls installed, making adjustments to your heater would require you to take trips outdoors.
Expert tip
I suggest that buyers consult a plumber before ordering to be sure they buy a unit with proper specifications for their home.
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Maintaining your tankless water heater
If it’s low maintenance you want, an electric tankless water heater is your best bet.
Every six months, the unit should be flushed with white vinegar to break up any mineral deposits that hard water may leave behind. The appliance’s filter should also be soaked in white vinegar during this process. The manual that comes with your unit will provide instructions on how to access the filter and flush the internal components appropriately.
Keeping your heater free from lime and mineral buildup helps ensure that the water flows freely and makes contact with its heating elements.
Price
$120 to $200
While there are models in this low-price band, they come with a lot of limitations. Some are only powered by propane, which adds complexity to the installation and ongoing use. Others are geared toward warmer climates and instances where only one usage (such as a sink) is needed.
$200 to $400
In this price range, some models use propane fuel or are built for a single purpose, such as an outdoor shower. There are also some electric tankless models with lower wattages, which translates to less power. Units acceptable for smaller homes in temperate climates can be found in this range.
$400 to $500
Electric tankless water heaters in this price range deliver better performance. For example, you are likely to get greater efficiency and more water flow on demand. Some models must be installed close to the point of use (within 50 feet), but that is offset by the fact most claim to be easy self-installs.
These models provide greater flow capacity, and they’re more likely to offer additional features, such as digital temperature settings and Wi-Fi.
$500 to $2,000
If you want a unit that will provide a lot of hot water on demand with a strong flow to multiple points of use, it will cost you $500 to $2,000. Along with the everyday excellent performance, these premium models typically have longer warranties, top-tier customer service and great durability.
Expert tip
Some tankless units are WiFi enabled so you can monitor and regulate from your phone.
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FAQ
Q. Does a tankless water heater change the way I use the shower?
A. For best results, manufacturers recommend that you turn the hot water on high, allow the water to heat, then cool the delivered water by opening the cold-water tap. This allows the tankless water heater to run at top efficiency while you make fine adjustments via the amount of cold water being mixed in.
Q. How long does it take for the water to actually get hot?
A. Most tankless water heaters reach their peak temperature and start heating the water within seconds of tap activation. The slight lag you experience in receiving hot water depends mostly on the distance between the heater and the tap.
Q. If the power is out, will my electric unit still work?
A. Most electric tankless water heaters will still allow water to flow when your power is out. However, the heating element won’t warm the water unless you have a battery backup or some other source of electricity, like a generator.
Q. Are tankless water heaters impacted by altitude?
A. Altitude matters for tankless units. At 4,000 feet, a gas unit begins to lose its efficiency at a rate of 4% per 1,000 feet. Electric models are not affected.
Q. What are the biggest downsides to using a tankless water heater?
A. In addition to the high price and expensive installation, another downside to tankless water heaters is that they can only heat so much water at a given time. While the supply may be endless, running too many appliances at once could result in temperature fluctuations if the unit is unable to keep up with the demand.
How we analyzed
We researched dozens of options before narrowing our list down to the five best tankless water heaters. We weighed the pros and cons of gas versus electric models and indoor versus outdoor options. We looked at specs such as voltage, size, the number of water connections and output temperature range. And naturally, we factored in the cost of each model and explored whether it offered enough quality and features to justify the price.
Our expertise
Using a combination of in-house testing, trusted consumer feedback and a shared thrill of seeking out the absolute best products, devices and tools, BestReviews is your number-one resource when it comes to reviews you can count on. Our staff brings you real advice from people who share your passions and seek to make every day a little easier, a little better and a lot more fun.
Derek Walborn is one of BestReviews’ trusted lawn, garden and DIY experts. Providing insight since 2021, Derek has written extensively on topics that range from home security systems and propane grills to the latest power tools and home improvement gadgets.
