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Tankless Water Heaters for The Bathroom: Pros And Cons

a woman stands shivering under a cold shower

A tankless water heater for the bathroom can provide hot water on-demand. At about a tenth the size of a traditional unit, these units not only reduce clutter but also are great for the environment.

Initial costs are more expensive than traditional storage systems, but a tankless water heater is more energy efficient in the long run. 

I spoke to Bob Lemons, the owner and operator of Mr. Tankless. He dominates the tankless water heater installation market in Central Texas, installing more than 300 every year.

Read on to get Bob’s expert advice regarding choosing a unit and how to save big money.

Is a Tankless Water Heater Good for a Bathroom?


No matter the size of the space or how many people will be using the bathroom, an instant tankless water heater will always supply the amount of hot water needed on demand.

Benefits of Tankless Heaters

There are many benefits to fitting a tankless water heater in a bathroom:

  • They are cheaper to operate as they don’t have to store the water to keep it warm.
  • They have a longer life span than a traditional boiler-style heater
  • Water is always hot on demand.
  • Clutter-free!

Mr. Tankless puts it like this:

“Tankless is the way to go if you have more than one shower head or garden tubs that you can’t fill. If you try to fill a 60-gallon jacuzzi tub [with a conventional storage tank water heater], you’d get a quarter of the way before you start running out of hot water. With tankless, you can fill a large tub and enjoy a nice bath. You’re not ever going to run out of hot water.”

He says usually the tankless water heaters are used to supply the entire home, including the bathrooms.

Essential for Energy-Efficient Bathrooms

The tankless appliance is essential to create the most ecofriendly bathroom possible. But exactly how ecofriendly are they?

According to the US Department of Energy:

“For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters. They can be 8%–14% more energy efficient for homes that use a lot of hot water — around 86 gallons per day.”

Other ways to save water in the bathroom include reusing bath water to do laundry or water your garden.

How Do Tankless Water Heaters Work?

How Tankless Water Heaters Work

In most homes, a standard boiler tank is the traditional storage unit. Generally, electricity, natural gas, or propane are used to power the element inside the boiler and keep the water hot.

Boiler Storage Tank

A boiler storage tank can safely store from 30 to 60 gallons (136 to 272 liters) of water at any one time. It uses an enormous amount of power to keep the water at a constant temperature. Then, as the water is emptied from the boiler, fresh water is pumped in using more power to heat the fresh water to reach the correct temperature.

How the Tankless Water Heater Works

A tankless appliance provides on-demand hot water. This means that whenever you need hot water and open a faucet, cold, fresh water enters the tankless unit.

Next, the burner is activated and the water is heated to the correct temperature as it passes through the burner.

Finally, you receive hot water from your faucet or outlet pipe, almost instantly!

The heating unit automatically turns off when you switch off your faucet.

Two Types of Tankless Water Heaters

There are a wide range of tankless water heaters available. These include mini heaters, compact heaters, and even comfort heaters.

Tankless water heaters are powered either by electricity or gas. The electric models are more popular since they last longer, are typically smaller units, and are easier to install. 

1. Gas-Powered

Gas-Powered Tankless Water Heaters

Gas-powered tankless water heaters produce a higher water flow rate (gallons or liters used per minute) than electric models. For example, a gas-powered water heater can heat a flow rate of up to 5 gallons (22 liters) of water per minute 70 degrees Fahrenheit (21 degrees Celsius). A gas-powered water heater is an excellent option for larger homes that use a lot of water. 


Gas models are substantially more expensive than electric tanks. Also, they need to be installed by a professional and require good ventilation. 


Gas-powered water heaters also need an annual maintenance check to keep them in good condition, but they have a potential life span of around 20 years or more, so they are worth the upkeep!

Natural Gas or Propane

The Rinnai Tankless Hot Water Heaters run on natural gas or propane, and can provide 5.3-9.8 gallons per minute, depending on the model. You do need to purchase a special vent pipe for these units. Though you invest upfront, you can recoup and then some when paying your water bill. 

Mr. Tankless Says…

Mr. Tankless says gas-powered tankless water heaters typicallylast much longer than electric units. Plus, he says, you’ll save significantly on your monthly gas bill. According to energy.gov, gas-powered tankless water heaters generate higher flow rates than electric ones:

For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters. (source)

Mr. Tankless recommends Rinnai gas-powered models. “The Rinnai has been around the longest. They have great warranties. And the unit is solid,” he tells me.

2. Electric-Powered

Ecosmart ECO Electric Tankless Water Heater on Amazon

Electric-powered tankless water heaters are cheaper to install than gas models and you can safely place them anywhere in your home—including the bathroom!— since they do not require ventilation. 

Flow Rate

Once you have determined the required flow rate for your needs, you can typically choose a water heater without worrying about overpriced installation costs. An electric-powered water heater can heat a flow rate of up to 2 gallons (9 liters) of water per minute 70 degrees Fahrenheit (21 degrees Celsius).


Electric-powered water heater units are not only much cheaper than gas heaters, but they also don’t require much maintenance and have a life expectancy of twice that of a traditional boiler storage tank!


For example, let’s look at the Ecosmart ECO 18 Electric Tankless Water Heater. Weighing in at only 14 pounds, it’s 90% smaller than a traditional water tank. Plus, it can be wall-mounted to save space and can heat from 1.8 to 4.3 gallons-per-minute. This can provide on-demand, endless hot water to your bathroom, while saving you up to 50% on your monthly water heating costs.

Where to Install a Tankless Water Heater

Woman turning regulate knob, adjusting temperature on boiler

When installing a tankless water heater, the only restriction is to leave access to the unit for maintenance purposes. Other than that, you can install a tankless water heater wherever you want it in your home or even outdoors.

You can even use the original hookups from the previous tank to save costs. And if you install a gas-powered unit, make sure that you have the correct dedicated connections and plenty of ventilation.

Installing the unit in the bathroom can maximize the water temperature and flow as the distance from the faucets to the water heater is shorter.  

Points to consider before installation are:

  • The distance to the water heater from the outlet pipe. If you install the unit in the basement and your bathroom is on the second floor, you might experience a delay in hot water reaching the faucet.
  • The distance from the water to anything combustible. Allow at least 24 inches for safety.
  • The safety regulations in your state or city. Discuss options with your plumber before deciding on a location.

What Size Tankless Water Heater for One Bathroom?

When you choose the size of the tankless water heater you want, consider:

  1. How many baths, showers, basins, and toilets will be used at any one time.

2. Next, work out how many gallons of water per minute (the flow rate) you need to supply each faucet and outlet.

3. Then look for a tankless water heater to provide the combined flow rate.

Tankless water heaters come in different sizes, so you might supplement a traditional water boiler by putting a tankless unit in each bathroom. This will ensure a good water flow to each tub and faucet.


The RX-13 Residential Tankless Water Heater by Rheem is the perfect size for on-demand hot water for a single bathroom, RV or apartment. See it here on Amazon.

Purchase the size of the water heater that will meet the demand. For example, a household with two occupants would only use a flow rate of 30 gallons (136 liters), whereas a home with five occupants could require 80+ gallons (363 liters) per use. According to Mr. Tankless, most bathtubs require 3-7 gallons per minute.

Follow this quick guide to determine the size of the tankless water heater that you need for your bathroom:

  1. How big is your house and how many rooms use water? Although water heaters vary in size, modern units can supply your entire home if you install one large enough for the job. 
  2. Determine how many faucets and outlets you need to run and their flow rate requirements. How many faucets you tend to run simultaneously should determine the size of your water heater, as the flow should be able to support the number of running faucets.
  3. What is the required temperature per faucet? The water heater should generate enough heat to supply the required heat to each faucet. 
  4. What is the water demand during peak usage times in your household? The water heater should be able to meet the requirements at your home’s busiest moments.
  5. Consider your budget and buy the biggest water heater that you can afford.

Considerations for Buying a Tankless Water Heater

Before purchasing a tankless water heater for your space, research which type of heater, either gas or electric, would be best for you. Consider which power source you have. If you choose to purchase a gas water heater, make sure you have adequate ventilation as well as a connection to the room where you plan to house the heater.

Here is an excellent video from ecosmart:

Select the Correct EcoSmart Model
  • Determine the correct size of the water heater that you will need,
  • Consider the climate in your area.
  • Consider the warranty of the water heater.

Pros and Cons of a Tankless Water Heater

Here are the top advantages and disadvantages of tankless water heaters:


  • Most tankless water heaters have a potential life expectancy of 5-20 years or more which is substantially longer than traditional tank-based systems.
  • As there is no bulky water storage tank, they are compact and can fit in any space, making them convenient and easy to install.
  • Instant hot water at a rate of 2 to 3 gallons (9 to 13 liters) per minute means that you don’t waste water while waiting for the hot water to flow through.
  • Tankless water heaters are more energy-efficient and only heat the water when you need it.
  • The constant temperature can be adjusted during different seasons, allowing for better energy consumption during the warmer months.
  • A tankless water heater will take up a lot less space in your bathroom than a traditional storage tank.
  • No chance of bursting storage tanks causing water damage in your home.
  • An intelligent investment when renovating or building a new property, adding value to your property.
  • Some water heaters are Wi-Fi capable and can be monitored and controlled by your smartphone.
  • Ideal for use in warmer and colder climates alike.

Cons :

  • A tankless water heater system is initially more expensive than traditional water boiler- systems.
  • You may need extensive renovations to accommodate the water heater system if the connections are only available for traditional water storage systems.
  • If your household water usage is high, a larger unit or even more than one unit may be required for your household use.
  • Most tankless water heaters need to be flushed once per year to prevent scale buildup. However, if you have hard water, you may need to flush the system two or three times per year.
  • As this system is tankless and does not have a water storage tank,  it cannot provide hot water during power outages. Even gas-powered tankless water heaters will not work in a freeze.
  • The hot water temperature can be inconsistent when multiple outlets are in use simultaneously.

Mr. Tankless Tells All! Installation and Rebates

Golden coins on bright background, online payment and refund

Here are wise words from Mr. Tankless:

First, get a certified tankless installer to do your work. Not just any plumber off the street. Why? Because these units can easily get messed up. And worse, if you don’t use a certified tankless installer, then you void the warranty. Mr. Tankless says:

“The manufacturers are very strict about who puts the product in. Installed correctly, these things are jewels.”

Second, check with your city about rebates. Because tankless water heaters are energy-efficient, many cities offer you an incentive to install one. On top of that, the US federal government offers a $300 tax credit. And on top of that, many manufacturers provide their own rebates. So spend an hour looking into this—it will pay off!

So Is a Tankless Water Heater Worth It?

boiler water heater electric tank
boiler water heater electric tank 3D

Here is our comparison list of the advantages and disadvantages of boiler-style systems compared to tankless water heaters. I used the electric water heater in the comparison.

Gas-Powered TanklessElectric-Powered TanklessGas-Powered Storage TankElectric-Powered Storage Tank
How They WorkOn-demand water not stored in tankOn-demand water not stored in tankWater stored in 30-60 gallon tanksWater stored in 30-60 gallon tanks
Price and Installation CostUnits are expensive and installation costs more than storage tankUnits are expensive and installation costs more than storage tankLess expensive; Easy DIY installationLess expensive; Easy DIY installation
PerformanceProvides a constant supply of hot water at 120 degrees Fahrenheit (48 degrees Celsius)Provides a constant supply of hot water at 120 degrees Fahrenheit (48 degrees Celsius)Gives a steady supply of hot water at 120 degrees Fahrenheit (48 degrees Celsius)Gives a steady supply of hot water at 120 degrees Fahrenheit (48 degrees Celsius)
Operating CostsAnnual operating costs average $195Annual operating costs average $535
Annual operating costs average $245Annual operating costs average $580
Energy ConsumptionExcellentFairVery GoodFair
Energy EfficiencyExcellentExcellent GoodGood
MaintenanceOnce a yearOnce a yearUnder warranty for 15 yearsUnder warranty for 15 years
Size of UnitSmall and compactSmall and compactBig and bulkyBig and bulky
LocationAny space if connections are supplied, indoors or outdoorsAny space if connections are supplied, indoors or outdoorsOnly where size allowsOnly where size allows

*Table data on energy consumption, energy efficiency and operating costs is from Consumer Reports.

Tankless Water Heater for the Bathroom?

Tankless water heaters are not for everyone. They require more upfront investment while providing cost savings in the long run. And because they don’t routinely heat all the water in a traditional tank, they are the most energy-efficient solution on the market.

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