Point-of-use water heaters (POU) are small heating devices designed as the mini storage tanks or tankless units, built as electric or gas-powered, heating water instantly and supplying mainly one fixture with hot water. They can be used in new or added to an existing systems (retrofits), often installed under the kitchen or bathroom sink. This is why they are also called under-sink water heaters.
POU units are very popular in residential and commercial applications with the limited space and where the 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 installed at each fixture, or in combination with the large heaters to boost the heating and increase the comfort.
Top 3 selling POU tank-type models
Top 3 selling POU tankless models
POUs have several advantages.
If you live in a house that has a distant sink and it takes a long time to receive hot water from the central unit, installation of 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 heaters can also be used if there is a remote sink that is not served by a tank-type or tankless water heater, and where retrofitting is either too expensive or impractical to do.
In a case of the large buildings, contractors might choose, instead of the high-capacity tank model, several POU units, therefore minimizing the wait time for hot water delivery significantly. As the units are dedicated to only one location they will provide a 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 sandwiching” and increasing the comfort.
The POU water heaters, if installed as recommended, can actually save money. This includes 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 having the ability to adjust the water temperature on the spot as long as the units are installed with an easy access.
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 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 are popular.
The best point-of-use water heaters are equipped with some great components which can help prolonging the heaters life, increase the performance and efficiency, save on energy, and even automatically control the system.
Most of the 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 heater, that doesn't corrode.
Heaters are usually equipped with only one screw-in style heating element with the 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 it into any standard outlet, while 240 V models include a junction box for easy installation.
With its space-saving design, 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 manufacturer 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, 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, which eliminates the need for recirculating lines and pumps. Some models can be installed horizontally while other vertically.
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.