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Tankless, or "on-demand" water heaters, are popular because they give precisely the amount of hot water you need. This type of water heater can save you money because you don't end up heating dozens of gallons that just sit in a tank, waiting to be used. An efficient unit will save you a considerable amount of cash, but the market is home to a wide variety of different models, and it's important to choose the one that best suits your family's hot water needs.
At BestReviews, we want to help you pick the perfect tankless water heater for your home.
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Our thorough research reveals the top five tankless water heaters on the market today. These contenders span a variety of needs and budgets.
Tankless water heaters only heat water when you need it, so minimal energy is wasted. That doesn't mean they're all the same, though. Each product has ratings for the amount of heat it generates — in British Thermal Units (BTUs) or kilowatts (kWs) — and the actual volume of water delivered — usually in gallons per minute (GPM). Both of these factors must be considered to ensure you'll have enough hot water for your needs.
Both electric and gas models are available, and each has different installation requirements. Day-to-day performance levels also vary, depending on the model.
We take a look at temperature adjustment: you might adjust water temperature with a simple knob, or you might rely on a panel of complex, automated flow controls for temperature adjustment. We also examine warranty and safety features. Safety features are particularly important if you're considering a gas-powered water heater.
Water heaters are expected to work hard for many years, so it's not surprising that they're not cheap. Having said that, we've found excellent units for your consideration across a number of price brackets.
The Eccotemp FVI-12-NG Gas Tankless Water Heater has a flow rate of 3.4 GPM and a BTU rating of 74,500. While BTUs are often quoted as "heat,” a BTU is actually the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit. In practical terms, most people find BTUs are good for comparison rather than as a specific measure.
The Eccotemp is designed for small and medium-sized homes. Considering the fact that a shower uses approximately 2 to 2.5 GPM, you can see that the Eccotemp could potentially provide hot water for a kitchen faucet at the same time someone is taking a shower – but not much more than that. This doesn't mean the Eccotemp is inefficient; it's simply designed for lower-usage households.
The Ecosmart ECO 27 Electric Tankless Water Heater produces 27 kilowatts of energy, which is equivalent to approximately 92,000 BTUs. Interestingly, the company quotes two different flow rates for this product, depending on your location. If you're in the northern U.S., where incoming water temperature can be only a couple of degrees above freezing – and therefore quite sluggish – the rate is quoted at 3 GPM. If you're in the south, flow rate is quoted as high as 6 GPM. We give kudos to Ecosmart for this refreshingly honest marketing approach.
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The Takagi T-KJr2-IN-NG Gas Tankless Water Heater's energy output is rated at 140,000 BTUs. Flow rate is quoted at 6.6 GPM. Takagi's product description rates this model as ideal for small homes, yet the company also boasts that this product has the capacity to supply radiant floor heating. Given that the Ecosmart, at 6 GPM, can run several showers simultaneously, it's reasonable to expect that the Takagi can deliver a similar real-world output.
Where the Ecosmart provides two different flow rates based on temperature, the Stiebel Eltron Tempra 24 Plus Electric Tankless Water Heater provides two entire charts: one for 240-volt input and the other for 208-volt input. Using the former, this 24 kW (82,000 BTU) water heater boasts a flow rate of 2.6 GPM at 40°F, rising to a maximum of 5.4 GPM at 75°F. According to the company, the lower output is more than sufficient for a hot shower, while the higher output is suitable for Roman or jacuzzi tubs.
At 7.5 gallons per minute, the Rinnai RL75iN Gas Tankless Water Heater offers a considerably higher flow rate than any of the others in our top five. According to the manufacturer, BTU output varies from 10,300 to 180,000. This quoted range is actually a more accurate reflection of output than that of other companies who simply quote BTU maximums. The Riannai is also the only water heater on our shortlist to deliver temperature ranges up to 140°F for household installations (the Department of Energy says a maximum of 120 is sufficient for hot showers), and 160°F for commercial installations (an additional controller must be purchased in order to achieve this).
Water heaters are rated in BTUs – the amount of energy required to heat or cool one gallon of water. Typically, the higher the BTUs, the better the unit.
The Eccotemp FVI-12-NG Tankless Water Heater uses natural gas and, as such, needs to be vented to the outside of the building. The vent kit is supplied and comes out of the back of the unit, horizontally, which is something consumers must keep in mind during installation. As with any water heater, customers will need to purchase appropriate water and gas valves separately or have the heater installed by a professional. At 15 x 24 x 4 inches, the Eccotemp is a tidy little unit which takes up a lot less space than a traditional water tank. All tankless water heaters require a minimum flow threshold before they will fire up; in the case of the Eccotemp, that level is approximately 0.9 GPM. Turning on the cold water can make the pressure drop, so consumers should plan on experimenting with the gas regulator and temperature controls in order to find settings they prefer. This characteristic is common to all on-demand water heaters, not just the Eccotemp. Although the Eccotemp is a gas water heater, it does require a standard electric supply of 110 volts.
Because it runs on electricity, the Ecosmart ECO 27 Tankless Water Heater is somewhat easier to install than a gas unit. Although many users have installed the Ecosmart themselves, the process is still complicated enough that some owners choose to hire a certified electrician to do the job. At 17 x 17 x 3.5 inches, the Ecosmart is a space-saving unit with 3/4-inch NPT fittings that allow greater flow rates than ½-inch fittings – although the minimum GPM required to activate the Ecosmart is just 0.25.
If your unit uses natural gas, it will have to be installed outside. Otherwise, many households have their units indoors which can make it easier to heat the water.
The Takagi T-KJr2-IN-NG Tankless Water Heater is a gas-fed model which needs venting to the outdoors. Unlike the Eccotemp, owners of the Takagi have the option of venting horizontally or vertically. Connections for both gas and water are 3/4 of an inch, allowing for higher flow rates. Although we were unable to uncover a precise minimum activation rate, anecdotal evidence from our consumer research suggests it to be around 0.5 GPM. The water heater itself is 13.8 x 20.3 x 6.7 inches, making it slightly larger than the Eccotemp and Ecosmart but still a relatively compact unit. Like the Eccotemp, this heater requires a 110-volt electrical supply.
At 21.5 x 19.5 x 8.8 inches, the Stiebel Eltron Tempra 24 Plus Tankless Water Heater is a sleek and stylish unit. Although somewhat imposing, the Stiebel is still considerably smaller than a hot water tank. This heater can run on either 208 or 240 volts and requires 2 x 60 amp breakers, as it can draw as much as 115 amps at a time. Water connections, as you might expect, are 3/4 of an inch, with a minimum flow rate for activation of 0.58 GPM
Our final choice, the Rinnai RL75iN Tankless Water Heater, measures 14 x 23 x 9.3 inches. It is possible to convert this natural gas model to propane. The Rinnai is vented from the top but could be made horizontal with the appropriate fittings, giving consumers the option of going through the wall or roof. All of the Rinnai's gas and water fittings are 3/4 of an inch – a necessity considering the flow rate of the product. A 120-volt electrical supply is required for this model's digital controller. We were unable to obtain a minimum flow rate quote from the manufacturer, but some owners have hypothesized that it's around 0.4 gallons per minute.
Additionally, we should mention that the Rinnai requires periodic maintenance, just as all tankless water heaters do. Usually this means little more than an annual flush with a cleaning agent like white vinegar, but owners should always consult manufacturer recommendations for proper maintenance tips.
You should try to flush your unit once a year with white vinegar or another cleaning agent in order to keep it running cleanly.
For safety reasons, the Eccotemp FVI-12-NG Gas Tankless Water Heater features a “powered” or "forced" vent which expels noxious gases outside. This vent helps maintain the efficiency of the unit, ensuring consistent performance over time. A digital temperature display, along with separate manual controls for gas flow and water temperature, help balance your hot water needs. The Eccotemp comes with a two-year warranty.
Most tankless water heaters are purported to save you approximately 15-20 percent in energy bills over what you'd pay with an old-fashioned tank. The Ecosmart, however, claims to save its customers up to 50 percent. Ecosmart attributes this savings to its “self-modulating technology” which precisely regulates the amount of energy required to heat household water. Precision seems to be a focus of the Ecosmart manufacturer; many energy-conscientious customers we surveyed appreciate the fact that temperature can be digitally controlled in one-degree increments using this model. The company backs its this product with a lifetime warranty.
While some tankless water heaters can be installed on your own, it’s always safer to have a professional do the job in order to guarantee the unit is most efficient.
The Takagi T-KJr2-IN-NG Gas Tankless Water Heater ensures consistent water temperature through the use of thermistors, a kind of resistor that reacts to changes in heat. It features an air-fuel ratio (AFR) sensor which monitors efficiency and, as a consequence, reduces harmful emissions. The Takagi also offers exhaust and water temperature safety controls; this unit turns itself off in the event of overheating and guards against frost as well. The Tagaki warranty promises five years of protection for parts and ten years for the heating element, but only if the unit is installed by a registered professional.
The Stiebel Eltron Tempra 24 Plus Electric Tankless Water Heater features a nicely designed, front-mounted dial that offers a visual analogue guide to temperature as well as a the digital readout. Because the Stiebel isn't a gas unit, safety features are less of a concern. Instead, Stiebel Eltron highlights its Advanced Flow Control, a feature that maintains temperature automatically. Many of the owners we surveyed speak highly of this feature; one customer told us he loves the Stiebel's “unlimited hot water.” The Stiebel's warranty is surprisingly short at only three years. Just like the Takagi, the warranty is promised by the company only if a licensed professional installs the unit.
The Rinnai RL75iN Gas Tankless Water Heater is the only machine in our ratings that is certified by Energy Star. It features a series of digital controls and monitoring sensors that provide all the necessary safety features. The Rinnai also offers “scale detection,” a feature that takes the guesswork out of maintenance periods, thereby preventing long-term internal damage. Customers like the Rinnai's temperature lock function; this feature ensures that nobody else can tamper with the heat settings you choose. The Rinnai warranty guarantees one year for labor, five years for parts, and twelve years for the heat exchanger. Like other models on our shortlist, the Rinnai must be professionally installed in order for the warranty to take effect.
Never flush your tankless water heater with any chemicals. Most likely your drinking water is running through the heater and chemicals could be poisonous.
At $269, the Eccotemp FVI-12-NG Gas Tankless Water Heater is the cheapest of our top five. It's designed for small to medium-sized households and very popular. Comments like "Perfect for my two-bedroom, one-bathroom house!" are typical, and most of the complaints that surfaced during our research came from two separate camps: people who misjudged the type of tankless water heater they really needed, and people who didn't like the amount of water pressure produced by the Eccotemp. Given that the Eccotemp produces the highest minimum water pressure required, this type of consumer complaint underlines the importance of making an educated decision before investing in a product. Sometimes the cheapest model suits your needs just fine; other times, it doesn't.
The Ecosmart ECO 27 Electric Tankless Water Heater sells for $434. This model is easier to install than a gas unit, but running costs will depend on local supplier rates. Homeowners and professionals alike give the Ecosmart high ratings. Comments like “I've saved a lot of money on my energy bills!” and “I never run out of hot water!” are common. During our product research, we discovered that many owners actually get better performance than suggested by the manufacturer. One happy owner with three children and two-and-a-half baths told us he enjoys consistently hot water thanks to his tankless heater. The Ecosmart is also the only water heater on our shortlist that offers a lifetime warranty.
Whenever performing maintenance on your tankless water heater, always turn it off and turn off the water valves connected to it before tinkering
The Takagi T-KJr2-IN-NG Gas Tankless Water Heater offers tremendous savings at $499. It's a popular unit with both home owners and renters. One plumber we spoke to rated the Takagi as an ideal water heater for families of five or less. Another owner told us his Takagi has been supplying his home with hot water successfully for 10 years now. While some of the users in our survey found the Takagi relatively easy to install, others strongly suggested calling in a professional. Professional installation is the only way to validate the Takagi warranty, so this would be the best route for most consumers. The few criticisms we uncovered related to the Takagi's cost of installation, but installation costs could be considered to be a “drawback” for any gas tankless water heater.
You can get a Stiebel Eltron Tempra 24 Plus Electric Tankless Water Heater for $799. The company claims their product to be the most technologically advanced machine on the market, although its competitors make similar arguments. One of the Stiebel's greatest consumer advantages is its accurate temperature control. Several owners we surveyed have set it, measured the output, and reported that they got exactly what they expected. One owner, a resident of Canada where input water is just 40 degrees, said the Stiebel "boils me like a lobster!" It's difficult to imagine higher praise than that; indeed, we had a hard time finding anyone who had a bad word to say about the Stiebel.
The Rinnai RL75iN Gas Tankless Water Heater sells for $1131. It's an efficient and technically accomplished unit that can produce hot water on demand for numerous bathrooms and appliances at the same time. We've heard many positive comments from owners, such as "Fantastic unit!" and "Works perfectly!" However, our research also turned up a sprinkling of negatives. While some of the negatives had to do with people misunderstanding the product's requirements, a few related to quality-control issues.
We give the Stiebel top ratings for its honest marketing approach and its unlimited hot water supply. You simply cannot buy a better tankless water heater.
At BestReviews, we purchase every product we review with our own funds. We never accept anything from product manufacturers. Our goal is to be 100% objective in our analysis, and we do not want to run the risk of being swayed by products provided at no cost.