Point-of-Use Water Heaters: Buying Guide, Pros and Cons

Point-of-use water heaters (POU) are small heating devices designed as mini storage tanks or tankless units, built as electric or gas-powered to heat water instantly and supplying mainly a single fixture with hot water. They can be used in new or added to existing systems (retrofits), often installed under the kitchen or bathroom sink. This is why they are also called under-sink water heaters.

Bosch point-of-use water heater (POU)
(photo: amazon)

What are the point-of-use water heaters?

POU units are very popular in residential and commercial applications with limited space and where a simple solution is needed to provide hot water fast.

Point-of-use water heaters are not designed for large volumes of hot water but to serve low volume fixtures such as lavatory sinks, in small apartments, cottages, garages, including mobile homes (RVs).

POUs are mainly used for a single application, as the individual units are installed at each fixture or in combination with the large heaters to boost the heating and increase comfort.

Top-selling models

Top 3 selling POU tank-type models

• Bosch Tronic 3000 T
• Ecosmart ECO MINI 2.5
• Stiebel Eltron SHC 2.5

Top 3 selling POU tankless models

• Ecosmart POU 6
• Stiebel Eltron DHC-E 8/10
• Rheem RTE 13

Advantages

When comparing to other types, POUs have several advantages.

If you live in a house with a distant sink and takes a long time to receive hot water from the central unit, installing the point-of-use hot water heaters will reduce the wait time, water, and energy usage. They are near 100% energy efficient.

This type of heater can also be used if a tank-type does not serve a remote sink or tankless water heater and where retrofitting is too expensive or impractical.

In the case of the large buildings, contractors might choose several POU units instead of the high-capacity tank model, therefore minimizing the wait time for hot water delivery significantly. As the units are dedicated to only one location, they will provide steady hot water flow.

Also, when these mini tanks are installed in line with the tankless models, they operate as a buffer minimizing the temperature fluctuation, known as "cold water sandwich," and increasing the comfort.

If installed as recommended, the POU water heaters can actually save money. This includes unit's installation close to the shower, washing machine, and in the kitchen, by the sink.

The idea is, as mentioned before, to make the distance between the heat source and the faucet as short as possible.

Another great advantage is the ability to adjust the water temperature on the spot as long as the units are installed with easy access.

Disadvantages

• POU units are not suitable for applications with high hot water demand.
• Should not be used as the backup for the solar heating systems and geothermal heat pumps, as they cannot meet the demand when these do not operate.

Types

As said before, there are two types of point-of-use water heaters: mini-storage tank-type - with the capacity ranging from 2 gallons up to 30 gallons, and tankless with the low water flow but continuous supply.

Tankless point-of-use heaters are rated by the number of gallons per minute one unit provides, while tank-type units are based on the tank's capacity.

POU tank-type units are similar to large and tall models but mostly have one heating element with the thermostat.

Good examples of the electric mini-tank type are the Ariston from Bosch, SCH from Stiebel Eltron, Rheem 30-gal, while for the electric tankless POI models, Tempra from Stiebel Eltron and EcoSmart is popular.

Popular manufacturers

• Eemax
• Stiebel Eltron
• EcoSmart
• Bosch
• Rheem

Features

The best point-of-use water heaters are equipped with some great components which can help to extend the heater's life, increase performance and efficiency, save on energy, and even automatically control the system.

Most point-of-use heaters are equipped with the metal tank, but there are also models with the plastic tank, like Marathon point-of-use water heaters, don't corrode.

Heaters are usually equipped with only one screw-in style heating element with a power range from 1.5 to 2 kW, which transfers the heat directly and efficiently to the surrounding water.

Storage tank-type units are protected from the corrosive effects of hot water using the ceramic/glass coating combined with the anode rod.

Fully automatic control is achieved by using the surface-mount thermostat with the ECO, installed for safety in excess temperature situations.

Smaller units use 120 V and are supplied with the cord, which you can plug into any standard outlet, while 240 V models include a junction box for easy installation.

Installing tips

With its space-saving design, the point-of-use water heater is perfect for installation in the area with the limited space and where the standard type cannot.

These mini electric heaters can be mounted almost anywhere; in the kitchen and bathrooms under the sink, inside the cabinets of apartments and condos, hanging on the wall, standing on the floor, in camps and recreational properties, in stores, offices, and other places as the wash station.

The size of the POU heater you need depends on the area where it will be installed and the power supply. Smaller size units are mainly used for jobs like hand-washing, while larger models with the higher flow are used for dish-washing, shaving, showering, even supplying more than one fixture.

Note: Always use the manufacturer's recommendations and the manual when installing the point-of-use water heater. You can install the heater as the independent unit or as part of the in-line installation, together with other heaters such as tankless, for example.

These can be installed directly at the sink, on the cold supply line, and as close as possible to the hot tap, eliminating the need for recirculating lines and pumps. Some models can be installed horizontally while others vertically.

Summary

POU water heaters are recommended to buy for homes and businesses where a small amount of hot water is needed, where there is not enough floor space for installation of the traditional cylinder type, and as a buffer helping tankless.

By installing the unit close to the point of use, the pipes get shorter, heated water delivered fast, resulting in energy, space, time, and water savings, easy and fast installation, and increased comfort.