The Best Tankless Water Heaters of 2021

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The Best Tankless Water Heater Option


Traditional storage tank-style water heaters aren’t nearly as efficient as their tankless counterparts. Tankless water heaters typically increase energy efficiency by 24-34 percent, according to the U.S. Department of Energy.

Read on to learn more about tankless technology and to get our top tips on choosing the best tankless water heater for your needs and budget. Plus, don’t miss our roundup of top-favorite picks below!

  1. BEST OVERALL: Rinnai RU160eN
  2. RUNNER UP: Rheem 240V Tankless Water Heater
  3. BEST ELECTRIC: Stiebel Eltron Tankless Heater – Tempra 36 Plus
  4. BEST PORTABLE: Hike Crew Portable Propane Water Heater
  5. BEST POINT OF USE: ECOTOUCH Tankless Water Heater
The Best Tankless Water Heater Option


Before You Buy a Tankless Water Heater

Tankless water heaters are growing in popularity, for a host of justifiable reasons. However, there are a few considerations to take into account.

Tankless heaters typically cost more than traditional units—between $1,000 and $3,000, not including installation. With installation costs included, the price tag can rise to as much as $6,000. For storage-tank models, meanwhile, the installed cost of a new unit tends to run between $1,000 and $2,000.

Another important consideration is how much hot water your household requires each day. If multiple showers, a clothes washer, and a dishwasher are all expected to operate simultaneously, a tankless model may have trouble providing a sufficient volume of hot water. (Some large, busy families opt to install multiple tankless water heaters for this reason.)

Consider installation, too. If your home has a storage-tank heater right now, the existing electrical wiring, gas piping, water piping, and ventilation (for gas models) may need to be reconfigured to fit a tankless unit. For that reason, installation of a tankless water heater typically takes longer and costs more.

What to Consider When Buying a Tankless Water Heater

Immediate access to hot water and reduced energy consumption throughout the year are just a few of the benefits of a tankless water heater. To choose a tankless water heater based on features that will be most beneficial to your home, keep in mind the following.

Fuel Type

There are three main types of fuel for a tankless water heater: natural gas, propane, and electricity. Gas models operate at a higher power output than electrical models, heating more water to the ideal temperature for a lower cost. The downside to this is that the initial cost of a gas tankless water heater is about $1,000 more than that of an electric heater. The installation is usually more complex, too.

  • Natural gas usually costs less than propane or electricity and, in many homes, can be directly piped in. This style of tankless water heater is a great long-term investment, as the lower cost of natural gas can eventually make up for the higher cost of the unit. Natural gas is also a good choice for high-demand households. Because natural gas is not easily stored, these models are poor choices for use in an RV. Also, keep in mind that if your home does not have existing natural gas hookup, running a line to your home may add prohibitively to the total installation cost.
  • Propane gas is the most expensive and often cannot be piped into a home. Rather, a tankless water heater that runs on propane is typically fed by a portable fuel tank, positioned directly next to the water heater. The tank must be replaced when empty, making propane-powered tankless water heaters somewhat impractical for home use but perfect for use in recreational vehicles.
  • Electric tankless water heaters are an affordable choice, both in terms of initial purchase and installation. That said, the high cost of electricity—and the high electricity consumption of water heaters—can even out the cost in a hurry. Electrical models also have higher power requirements than many older homes are able to meet. If the current electrical system does not meet the manufacturer’s specifications, a costly upgrade to the electrical system could be necessary.

Flow Rate (GPM)

A tankless water heater’s flow rate reflects the maximum volume of hot water that the tank is capable of producing. Flow rate is measured in gallons per minute, or GPM, with each fixture—the bathroom tub, for example, or the kitchen sink—requiring a certain level of flow to operate as expected. For example, a tub uses about 4 GPM, while a shower uses approximately 3 GPM.

Homes with more than four adults should consider tankless water heaters with a flow rate of 7.5 to 8 GPM, while those with fewer than four adults should be fine with a flow rate of 3 to 5 GPM.

When determining the flow rate necessary for your individual home and your individual needs, consider the amount of water used all at once in the household. If few fixtures are ever in use at one time, a lower flow rate is adequate. However, if multiple showers, a dishwasher, and a couple of sinks are likely to run simultaneously, a lower flow rate will fall behind the home occupants’ needs.

Whole-house tankless water heaters are larger and more powerful than point-of-use tankless water heaters. These models provide hot water to an entire house and have much higher flow rates and power inputs. Point-of-use designs are intended to be used on a single fixture, so they require only enough flow and power input to heat one shower, say, or one sink. These are great if you can afford multiple tankless water heaters or plan to use your point-of-use unit in conjunction with a traditional tank model.

Power Input (BTU)

The energy required to heat water to a target temperature is called the power input. This is measured in British thermal units, or BTUs. A BTU refers to the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit.

To decide on the necessary power input for your tankless water heater, consider a simple situation. Assume the water coming into your home is 40 degrees Fahrenheit and that you would like your shower to produce water at a temperature of 120 degrees Fahrenheit. The tankless water heater would need to increase the temperature by 80 degrees. To do so, it would need 667 BTUs per gallon. A shower operates at 2.5 GPM, or 150 gallons per hour. To heat 150 gallons of 40-degree Fahrenheit water to a temperature of 120 degrees, a tankless water heater would need to produce 100,000 BTUs per hour, assuming 100 percent efficiency and a single fixture being in use. If the efficiency level drops or the use of another fixture is introduced, the minimum BTU requirement goes up.

The basic formula is:

(500 x GPM x Temperature Change = Required Power Input in BTU per Hour)

Efficiency Percentage

Where 500 (or 499.8 rounded up) is the weight of a gallon of water (8.33 lbs) multiplied by 60 minutes.

Use this formula as a starting point to calculate the BTUs required for your home and geographic location.


Gas tankless operate by burning fuel. When fuel burns, it produces exhaust that must be vented outside of the home, away from doors, windows, or any area that sees regular use by people or pets. The installation of ventilation piping can increase the installed cost of a tankless water heater, circumstances depending.

Condensing vs. Non-condensing

Steam or water vapor is a byproduct of the fuel burning in a gas tankless water heater. The steam is released to the outdoors through ducts or piping. The difference between condensing and non-condensing is when exactly steam gets released as part of the ventilation process.

  • Non-condensing tankless water heaters immediately vent steam. This necessitates the use of ventilation materials that are able to withstand high temperatures. These premium materials come at a cost, so installation prices can be higher. The heat lost through immediate ventilation also results in an efficiency rating of only about 80-85 percent. Non-condensing water heaters are typically cheaper to purchase.
  • Condensing tankless water heaters have a condensing unit that captures and reuses the residual exhaust heat before releasing a much cooler exhaust through ventilation channels to the outside. This style costs more money but produces about 98 percent efficiency.

Our Top Picks

Best Overall

The Best Tankless Water Heater Option: Rinnai RU160eN RRU160eN

The capabilities of the Rinnai RU150eN are impressive. The unit boasts a 9 GPM max flow rate that can produce hot water for multiple different fixtures, and the unit’s BTU maximum is more than enough for many average households. Despite this being a natural gas system, the Rinnai’s efficiency rating is admirably high. This is mostly due to a condensing feature that allows the water heater to remove as much heat from the exhaust as possible before releasing it through the ventilation.


  • High flow rate
  • Great for average households
  • Heats up quickly


  • Pricey

Runner Up

The Best Tankless Water Heater Option: Rheem 240V Tankless Water Heater

This little electric tankless water heater boasts an impressive 99 percent efficiency rating. It’s not the right choice for a large household where multiple fixtures are used simultaneously, but with a 4 GPM max flow rate and a 45,000 BTU maximum, it’s well suited to a small home with one or two occupants.


  • Compact unit
  • Highly efficient
  • Ideal for up to 2 people


  • Does not handle multiple fixtures simultaneously

Best Electric

The Best Tankless Water Heater Option: Stiebel Eltron Tempra 36 Plus Tankless Water Heater

The Stiebel Eltron tankless water heater boasts a 99 percent efficiency rating, silent operation, an impressive max flow rate of 7.5 GPM, and 92,000 BTUs in warmer climates. The unit’s Advanced Flow Control feature keeps water consistently hot during ongoing use, and a bold digital display shows accumulated cost savings.


  • Quiet operation
  • Cost savings displayed on screen
  • Easy to operate


  • Professional installation required

Best Portable

The Best Tankless Water Heater Option: Hike Crew Portable Propane Water Heater

Hike Crew’s portable, propane-powered water heater combines the luxuries of home with the ruggedness of camping. The built-in pump is placed into a water source and attached to a propane tank to provide ongoing hot water for camp showers, washing dishes, and rinsing equipment. Powered by AC/DC electricity, the Hike Crew portable comes with a hand faucet and shower head attachment, as well as some welcome safety features. For example, when the water runs out or reaches 125 degrees Fahrenheit, the unit automatically shuts off the burner. Capable of outputting 1 GPM with 42,000 BTUs, the Hike Crew isn’t great for all applications, but it’s ideal as a mobile unit.


  • Ideal for camping
  • Shower head included
  • Comes with a carry case
  • Lightweight


  • Low output

Best Point of Use

The Best Tankless Water Heater Option: EcoTouch Point-Of-Use Tankless Water Heater

As a point-of-use unit for a single fixture—be it a shower or a kitchen faucet—this small but mighty ECOTOUCH more than suffices. On the one hand, it boasts a flow rate of 1.5 GMP and 30,500 BTUs. On the other, it delivers a 99 percent efficiency rating, meaning that almost no heat is lost between the water heater and your shower, faucet, or other fixture. All the while, a self-modulation control monitors the water temperature to avoid fluctuations between hot and cold while the fixture is in use. This isn’t a whole-home unit, but it could be a great supplement in a bathroom or the kitchen.


  • Affordable
  • Almost no heat loss
  • Great supplemental unit for a bathroom or kitchen


  • Not suitable for an entire home

Our Verdict

For a reliable and high-performance unit to provide hot water to an entire household, the Rinnai RU160eN is an ideal option. For shoppers who enjoy camping but miss taking a hot shower, consider taking the Hike Crew Portable Propane Water Heater with you.

How We Chose the Best Tankless Water Heaters

The best tankless water heaters are energy efficient and robust enough to pump out enough hot water for an entire household. Our list of recommendations gathers products that stand out from their competition in terms of reliability, energy-saving features, and flow rate. We made sure to offer a selection of the most reliable units in the market that have impressive flow rates and efficient energy consumption, with options for both gas and electric units.

Our top picks also include some additional technology to help shoppers save extra on their utility bills while still being able to provide optimal levels of hot water. In our research, we also looked not only at power input, but also at venting options (such as direct-vent and power-vent), in order to provide recommendations that would be suitable for a range of household sizes.

We even made sure to include a portable option for those who enjoy the great outdoors but enjoy it even more if they can take a hot shower when desired.


Q: How does a tankless water heater work?

Tankless water heaters work by using a heating element (heat exchanger) to heat the cold water entering the unit. A flow-activated switch turns the heating element on as water is drawn through the unit by the activation of a fixture in the home. The water then flows through a series of loops within the unit, ensuring that it has enough time to reach the target temperature before exiting the unit and traveling to a fixture.

Q: What size tankless water heater do I need?

The size of tankless water heater required for your home depends on the number of occupants in the home, their day-to-day usage requirements, the size of the house, and the average temperature of the geographic area. (Lower average temperatures require increased output to heat water to the optimal temperature.) Homes with one to three occupants should look for water heaters that output 3 to 5 GPM. Homes with four or more people may require units capable of managing up to 8 or 9 GPM.

Q: How do you flush a tankless water heater?

The general procedure requires you to shut off the flow of electricity, water, and gas (if it is a gas unit) to the tankless water heater. Once done, connect hoses to the cold- and hot-water isolation valves. The hose connected to the hot water should not be connected to anything else, while the hose connected to the cold water should be attached to a pump.

Submerge the pump in a 5-gallon bucket filled with about 4 gallons of clean white vinegar, then place the open end of the hot-water hose in the bucket. Open the isolation valves and turn the pump on, allowing the pump to circulate vinegar through the tankless water heater for 45 minutes or an hour. After this, turn off the pump and empty the bucket.

Next, turn on the cold water to the unit, allowing the water to flow through and flush out the vinegar for five minutes.

Once completed, turn off the valves, disconnect the hoses, and return the tankless water heater to functionality by restoring water, gas (if it is a gas heater), and electricity to the unit.

Test to ensure the water heater is working correctly. If not, check your connection and ensure all power and fuel sources are properly restored. If a problem is present, consider contacting a local plumber for help.