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Point of Use Water Heater Buyers Guide: Tank-style and Tankless Water Heaters

Hot Water Handle

It's not uncommon to see a point-of-use water heater near a sink. Due to their small size, they're often tucked under the counter where they can warm your water, yet be out-of-sight. Some are even a good fit for recreational use. There are two basic designs on how they operate. They can hold hot water (tank-style), or  provide instant hot water (tankless).

Selecting the right style and size can be tricky, especially if you don't want to waste money on an overpowered unit that'll deliver more hot water than you'll ever need. As a general rule, the more money you're willing to pay, the more hot water your water heater will be capable of delivering.

Best Point of Use Water Heaters for 2019

Bosch Tronic 3000

Bosch Electric Mini-Tank Water Heater Tronic 3000 T 2.5-Gallon (ES2.5)  - Eliminate Time for Hot Water - Shelf, Wall or Floor Mounted

The Bosch Tronic 3000 Mini-Tank is one of the best selling point-of-use water heaters on the market. With three sizes to choose between (2.5-gallon, 4-gallon, and 7-gallon), you shouldn't have a problem finding the right one for your project.  


    The tank is glass-lined to protect it from corrosion, and it's well insulated to reduce standby heat loss. The unit has a thermal efficiency of 94%.
    Compact, lightweight and easy to install. It can sit on shelf or be mounted to the wall.
    The Tronic 3000 comes with a 6-ft cord that can plug directly into a standard 120-volt electrical outlet.


    The temperature is controlled with a dial, which makes it not as accurate as a digital control. However, for the price of the unit, this is a minor annoyance.

The Bosch Tronic 3000 is a great mini tank water heater. Like all tank-style water heaters, maintenance is an important part of service life, but with a 6-year limited warranty, Bosch is definitely standing behind their product.

This unit can be installed in-line with your main water heater to reduce your wait time for hot water, or used as a stand alone unit. The 6-foot cord allows plenty of flexibility when installing, and being able to plug it into a 120-volt electrical outlet saves you from hiring a electrician.

Product Details

  • Capacity: 2.5-gallons (but also available in 4 and 7)
  • Dimensions: 13.75" W x 13.75" H x 10.75" D
  • Voltage: 120v plug-in
  • Max Amp: 12 amps
  • Warranty: 6-year tank / 2-year parts

EcoSmart POU 3.5

Ecosmart POU 3.5 Point of Use Electric Tankless Water Heater, 3.5KW@120-Volt

EcoSmart has two sizes in their Point-of-Use line-up. The POU 3.5 which runs on 3.5 kW and requires 120 volts, and the POU 6.0. The 6.0 has a bit more punch, and requires 220 volts. Either would make a good choice, depending on your hot water needs.


    The EcoSmart line of tankless water heaters are extremely energy efficient. 99.8% of the electrical energy drawn goes to heating the water. This is an impressive number, even for electric tankless water heaters.
    The heat exchanger is stainless steel, and the heating elements are made of copper and brass.
  • The set temperature is displayed on the digital temperature control.


  • Requires hard wiring, even though the POU 3.5 only draws 120 volts.
    The 1-year warranty is a little tighter than many other manufacturer warranties, and the unit must be installed and registered within 30-days of purchase.

The EcoSmart POU 3.5 is designed specifically to be installed under the sink for a single application. EcoSmart does offer larger units that can handle multiple applications, such as a shower and a sink.

The POU 3.5 is ideal for a handwashing sink since it can deliver up to .50 gallons per minute of hot water. We recommend purchasing the POU 6.0 if you're looking for a heater to install in a wet bar or need just a little more power.

Installation is easy as no venting is required and the unit connects to a 1/2" NPT pipe fitting. The POU 3.5 is easy to operate and there are no filters to clean.

Product Details

  • Capacity: Tankless
  • Dimensions: 3" x 11" x 6"
  • Voltage: 120v
  • Amp: Requires a 30amp breaker and 10 AWG wire
  • Warranty: 1-year

Stiebel Eltron 2.5 Mini Tank

Stiebel Eltron 229729 4 gallon, 1300W, 120V SHC 4 Mini-Tank Electric Water Heater

It's hard to ignore Stiebel Eltron's products, they offer many different sized Point-of-Use tankless water heaters, but we especially like their Mini Tank series. These sleek European designed water heaters are available in three different sizes, a 2.5-gallon, 4-gallon and the larger 6-gallon model.


    Possibly the biggest advantage is the ease of installation. The 2.5-gallon can be plugged into a standard 120v electrical outlet. No need to call a electrician to hard wire it in.
    Stiebel Eltron builds their products to last. The tank is glass-lined to protect it from corrosion. 
    Making temperature adjustments are easy with the temperature adjustment dial located on the top of the unit. 


    Purchasing the right sized tank is critical. Once the tank is depleted of hot water, it'll take about 18-minutes for it recover. 

Stiebel Eltron's Mini-Tank can be used as a stand-alone water heater or plumbed in-line with your main system and used as a booster to deliver hot water faster. The tank is well-insulated to reduce stand-by heat losses and increase the energy efficiency of the unit. 

A wall bracket is included and no special wiring is required since it can be plugged directly into a standard 120v outlet. If you're looking for a tank-style point-of-use water heater, this is an excellent pick.

Product Details

  • Capacity: 2.5-gallons (but also available in 4 and 6)
  • Dimensions: 18-11/16" H x 11" W x 10-5/8" D
  • Voltage: 120v plug-in
  • Amp: 11.3 amps
  • Warranty: 6-year tank / 2-year components

Rheem RTEX-08

Rheem 240V Heating Chamber RTEX-08 Residential Tankless Water Heater

If you want a point-of use tankless with a little more power, you should take a look at Rheem's RTEX-08. The RTEX-08 is the smallest unit in Rheem's very popular RTEX line that can handle multiple applications. It's capable of delivering a maximum flow rate of 4.8 gallons of hot water per minute.


    Copper immersion heating elements with brass threaded top. Designed for easy replacement.
    External digital display shows the outlet temperature and can be adjusted in 1° increments so you can dial-in the perfect temperature.
    The RTEX-08 can be used for a single appliance, such as a shower or sink, or its powerful enough to provide hot water for multiple applications simultaneously.


    Although the RTEX-08 is a nice size for RV's, campers, and mobile homes, check your existing wiring before purchasing. It requires a 8 AWG wire size and a 40 amp breaker, which may not be available in all rigs.

Rheem is a trusted water heater manufacturer that offers a wide range of tankless and tank-style heaters. The RTEX-08 is perfect for situations when you need more hot water to service multiple applications. But Rheem does offer smaller units in this line-up, the RTEX-04 and the RTEX-06, which are designed exclusively for a sink.

The RTEX-08 is easy to install and comes with a 3-ft electrical cable. It'll need to be hard-wired to a 40 amp breaker, and it draws 240 volts. The unit fits nicely under a counter or a kitchen/bathroom sink. 

Product Details

  • Capacity: Tankless
  • Dimensions: 4" x 9" x 13"
  • Voltage: 240v
  • Amp: 33 amps
  • Warranty: 5-years heating chamber / 1-year parts

EcoSmart Eco Mini Tank

Ecosmart ECO MINI 4 4-Gallon 120V Electric Mini Tank Water Heater

EcoSmart is well known for their tankless water heaters, but did you know they also offer point-of-use mini tanks? Well, they do, and there are four sizes to help you find the right one for your needs. If you just need a handwashing heater, the Eco Mini 1 is the right pick for you, but if your looking for a little more hot water, check out the Eco Mini 2.5, or the Eco Mini 4, or even the Eco Mini 6.


    The tank is glass lined to protect against corrosion.
    Easy to install and can fit into small spaces.
    Power cord plugs into a standard 120-volt electrical outlet.
  • The heating element is replaceable and can be changed in the field.


    The recovery time is a little long at 24-minutes.

The EcoSmart Eco Mini Tank is a very versatile water heater. It's an effective heater for one or two hand sinks, but you can also plumb it to work as a booster to your main water heating system or if you have a gas tankless system it can solve the dreaded "cold water sandwich" issue.

Adjust the temperature with the easy to reach dial on the front of the unit. The power light let's you know when power is reaching the appliance, and the heating light is lit when water is being heated.

Product Details

  • Capacity: 4-gallons (but also available in 1, 2.5 and 6)
  • Dimensions: 16.25" W x 17.5" H x 13" D
  • Voltage: 120v plug-in
  • Max Amp: 12 amps
  • Warranty: 5-year leaks / 1-year parts


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5 Glasses being filled with water


How large of a point-of-use water heater should you purchase? Well, that depends on a number of factors. Since these small water heaters won't be used to deliver hot water to your entire home, there is more leeway in finding the right sized unit.

We'll take a close look at how to purchase both a tank-style unit and a tankless. But for now, you should know that each style measures capacity differently.

Tank-style water heaters measure capacity in terms of tank size, where tankless units use flow rate, expressed in GPM (gallons per minute). So, you should have a good estimate of how much hot water you'll need, especially if you plan on using it as a stand alone source of hot water.

Sole Provider

Many point-of-use systems are designed to have a variety of set up options. Some homeowners prefer to configure them so they are the sole provider of hot water for the source. They function entirely independently from the primary system. 


Others install the water heater to operate as a booster to the main hot water system. This allows the small heater to deliver hot water until the larger tank can take over. The video below provides more details.

Options on How to Configure a Point-of-Use Tank 

Types of Point-of-Use Water Heaters

As mentioned above, there are 2 different styles of point-of-use water heaters available: Tank-style and tankless. This article will cover both styles and what you should consider before making your buying decision.

Woman enjoying a hot bubble bath

Tank-Style Water Heater

A tank-style water heater uses a small tank to store the water until it's needed. Although, tank systems come in many different sizes, a true "small" water heater will have a tank size of 2.7-gallons to 7-gallons. But don't get caught-up in the "small" label. Focus on finding the right size to meet your needs.

Many top-of-the-line tank-style mini water heaters can be found for under $400, and some run far less. Stiebel Eltron makes a nice unit that's available in 3 different sizes, and Reliance has a popular 6-gallon unit.

How a Point-of-Use Water Heater Tank Works

Purchase Considerations: Tank-Style

Although, purchasing a tank-style mini water heater is pretty straight forward, there are a number of factors that you should consider to make sure you find the right size and set-up for your needs.


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Main Factors to Consider Before Purchase

To determine the correct sized tank there are 2 factors that you need to consider: 

  • Tank Size - How much water the tank can hold.
  • Recovery Rate - The time needed to reheat the water within the tank.

Finding the capacity of the tank size is pretty straight forward. The larger the tank, the more hot water you'll have readily available. However, the recovery rate is determined by the efficiency and wattage of the unit's heating elements.

A heating element with a higher wattage should deliver a shorter recovery rate. When the recovery rate takes less time to heat cold water, you'll spend less time waiting for the water to heat.  That may sound simple, but it can be a big deal . . . especially if you're using your small water heater for a shower!

Plumber holding hoses and tools

Configuration and Tank Size

As you've seen in the videos above, there are several ways to configure your small tank water heater. Frequently they are installed directly to the water line and function as a standalone unit.

If this is your chosen configuration, you'll likely be fine going with a small tank for the purposes of a hand sink or other low demand outputs.

However, if you're planning on using it for a shower, dishwasher, etc. you may want to err on the side of a larger tank. A tank-style water heater can only deliver the amount of hot water within it's tank. Once the tank is depleted you'll have cold water until the unit can recover (remember the recovery rate?)

If you're looking to give your main hot water system a boost, many units are designed with the option of installing it in-line with your home's main water heating system.  When you open the hot water valve, you'll immediately have hot water delivered by your small tank, thus eliminating the need to wait until the hot water runs thru the plumbing from your main unit.

Holding a small and large tape measure

What Size Should You Purchase?

Depending on your home's hot water heating configuration, if a small tank-style heater is used as a standalone unit to service a hand sink or other small output, a smaller sized tank will most likely meet your needs. EcoSmart makes 4 small units specifically for low demand usage, such as hand sinks

However, if it'll be used for a shower, dishwasher or other higher demand outputs, you may want to err on the side of a larger tank, or use it as a booster to your main system.

Woman enjoying a hot shower

Tankless Water Heater

Tankless water heaters are sometimes called flow-thru heaters because the water enters the unit cold and leaves hot. Since a tankless heater doesn't use a tank to store the water, the amount of water the unit can deliver is determined by its flow rate.

The flow rate is measured in gallons per minute (GPM) and it's the critical piece of information you need in order to properly size your water heater. Any small tankless water heater that delivers less than 2.25 GPM would fall in this category. Although a larger unit could be used as well.

There are many different brands available on the market today and most are below $300.​

How a Point-of-Use Tankless Water Heater Works

Purchase Considerations: Tankless

Selecting the right small tankless water heater can seem overwhelming. However, if you learn a few critical terms, it's actually not as hard as you might think.


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Main Factors to Consider Before Purchase

There are 2 key pieces of information to take into account to properly size the water heater to your needs: 

  • Flow Rate - How many gallons of water the unit can heat every minute.
  • Temperature Rise - How many degrees does the unit need to increase the temperature of the water. 

Let's take a closer look at each and cover how to calculate this information:

Flow Rate

Measured in gallons per minute (GPM), the Flow Rate is the amount of water the tankless is capable of heating at any given time. The higher the number, the more hot water your mini tankless water heater can deliver.

Most units fall in the range of .50 to 2.25 GPM. Keep in mind that finding the right GPM to meet your hot water needs can be the difference between taking a hot or cold shower!

Calculator and house plans
Calculating Flow Rate

You can determine your maximum flow rate by adding the GPM of each fixture that the tankless will be servicing. With a point-of-use heater, this isn't set in stone, but it is good to know, especially if your unit will be used as a stand alone water heater. This information is less critical when the unit is configured as a booster tank.

According to the 2010 Plumbing Standards, the average gallons per minute (GPM) is used for the following water outlets:

  • Standard Shower Head: 2.0 GPM
  • Water-Saving Shower Head: 1.5 GPM
  • Standard Hand Sink: .50 GPM
  • Bath Tub: Up to 4.0 GPM
  • Kitchen Sink: 1 to 2 GPM
  • Dishwasher: 1 to 2 GPM
  • Washing Machine: 1 to 1.5 GPM

Keep in mind that these are just reference points. If you are adding a tankless water heating system to service your entire home, you'll want to be very careful to get this right. But with a point-of-use system there is some leeway.

For instance, if you have a hand sink (.50 GPM) and a standard shower head (2.0 GPM), you might think that you should buy a unit that can deliver 2.5 GPM of hot water. However, you likely won't be servicing hot water in both outlets at the same time.

Also, if you plan on using your small tankless heater as a booster to your main water heating system (which is probably a really good idea if you are servicing a shower head) a much smaller tankless should work fine.

Temperature Rise

To determine the temperature rise, subtract the incoming water temperature from the hot water temperature. As an example, if the incoming water is 65-degrees, and your desired hot water temperature is 110, your temperature rise will be 45-degrees.

In other words, your tankless water heater will need to heat the water 45-degrees to bring it to your desired temperature. The higher the temperature rise, the lower the GPM the water heater will be able to deliver.

How Temperature Rise Impacts GPM

If, in the Winter, your tankless water heater needs to increase the incoming water temperature by 60-degrees (a 60-degree temperature rise) it may be able to deliver .45 GPM of hot water.

But, in the Summer, the temperature rise may only be 30-degrees, in which case, the unit's GPM may increase to 1.85. That's a significant difference and something to take into account . . . especially in cold climates.


When you begin shopping for a tankless water heater, you may notice that manufacturers tend to lead with the GPM a unit is capable of delivering. 

However, you often don't know the temperature rise they used for their calculations. That's why when you know your temperature rise you'll be able to accurately compare the water heater's efficiency.

Sizing a point-of-use heating system doesn't need to be exact. But if you have the basic information on how these units are sized, you'll be able to make an informed purchase decision and find the small water heater that best meets your needs.

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