Point of Use Water Heaters and Recirculating Pumps
Point of use water heaters and recirculating pumps save water and energy by eliminating the wait for hot water when you need it. They provide a fast, effective method for getting hot water instantly to remote faucets and fixtures in your home or business. By installing a point of use water heater right where it is used or a recirculating pump that delivers a continuous loop of hot water, you can have hot water instantly.
This guide will help you understand the different types of point of use water heaters and recirculating pumps in order to help you select the right water heating option for your needs.
Selecting a Water Heater
Selecting the right point of use water heater size and model is based on four simple criteria:
Use – How you plan on using the water heater will determine how much hot water it needs to supply. It will also determine if it’s advantageous for you to have a single unit for your entire home, individual units at each point of use, or a combination of both.
Configuration – A point of use water heater is most often used to augment a standard household hot water system but can also replace your central hot water heater with a series of point of use heaters. Consult a plumber and electrician to determine if a series of point of use water heaters will work for you.
Location – The area where your water heater will be installed and the availability of the power supply will help determine the capacity of the unit you select.
Tank or Tankless – Most point of use water heaters rely on a tank to maintain a ready supply of hot water, however some point of use water heaters are tankless and only heat water as needed.
How you use your water heater determines the type and size you need. For example, if you use the water heater sparingly for washing hands, you’ll need a smaller water heater than if you use it for more prolonged periods, such as for washing dishes.
Tank point of use water heaters come in a variety of sizes ranging from 2.5 gallons up to 20 gallons. For a single fixture where the hot water demand is low (hand washing, for example), a 2.5 gallon unit is often enough. If you plan on supplying multiple fixtures or have a greater hot water demand (dishwasher, washing machine, or a shower) you will need a larger capacity model.
Tankless point of use water heaters are rated by the number of gallons of water per minute (gpm) they provide. Identify how many of the fixtures and appliances you might have running at the busiest time of the day and select a water heater that provides the gallons per minute you require. Refer to the table of typical flow rates for fixtures and appliances below to get an idea of the minimum gpm you require for your point of use water heater.
Average Flow Rates in Gallons per Minute (gpm)
|Bathtub||2.0 - 4.0|
|Shower||1.5 - 3.0|
|Kitchen Faucet||1.0 - 1.5|
|Dishwasher||1.0 - 3.0|
|Clothes Washer||1.5 - 3.0|
Another factor to consider is if your point of use water heater will be used to augment a standard household hot water system or replace your central hot water heater with a series of point of use heaters.
• The largest point of use models are able to supplement a central water heater and can be installed if hot
water pipes have to run more than 70 feet from the central water heater. A 20 or 30 gallon unit will supply
hot water faster and can cover applications that use a significant amount of water like showering or
running a dishwasher.
• In many instances, installing a series of point of use water heaters can be a more economical solution to
installing a whole house system, with the advantage of continuous hot water wherever it is needed
throughout the home. Consult a plumber and electrician to determine if a series of point of use water
heaters will work for you.
Another factor to consider when selecting your point of use water heater is temperature rise.
Temperature rise is the difference between the temperature of your ground water and the temperature you want the hot water to be. A plumber can help you identify ground water temperature, or you can assume your ground water temperature is typically about the same as your annual air temperature. To calculate the temperature rise, subtract the temperature of the ground water (example: 65°) from the temperature you want the water to be (115°). The result, (50°), is the temperature rise you require from your water heater,
One reason why point of use water heaters are popular is that they provide instant hot water without taking up a lot of room. Many small models fit easily under a sink while larger models may need to be installed in a nearby closet. As a rule of thumb, six gallon models and smaller will fit underneath a standard vanity while larger models may have to be installed in a nearby closet. Be sure to measure the space where you plan to install your point of use heater to ensure it will fit before making your purchase. Additionally, take into account the room needed to install any plumbing on top or on the side of the unit.
Most point of use water heaters are powered by electricity, allowing them to be installed close to the point of use. Smaller units can often be plugged into a standard 120-volt (three prong) outlet, making installation simple assuming that a grounded electrical outlet is available. Larger units (6 gallons and above) may need to be hard wired before use.
Tank or Tankless
Tank-style point of use water heaters function in a similar manner to larger, whole house water heaters by storing water in an insulated tank until it is needed. They are typically limited to the amount of water they can heat per hour.
Instead of storing and constantly heating water, tankless models heat and deliver hot water only when it is needed. The performance of a tankless model is dependent upon the flow rate. The lower the flow rate, the greater the temperature rise. Many tankless point of use models are unable to function at more than 2.0 or 2.5 gpm, but they do not have the issue of running out of hot water like some of the smaller tank units. Tankless electric models may not be able to provide the hot water temperature required in some geographic areas with colder incoming water temperatures. Proper electric (kw) sizing is necessary. Based on the wattage / voltage requirements, special electrical modifications may be necessary. Check with a qualified electrician if you need assistance.
Recirculating pumps are a popular alternative to point of use water heaters. These pumps save you thousands of gallons in wasted water every year by turning your present plumbing system into a recirculating loop. Unused water in your pipes is continually returned to your central water heater, so you always have an instant, steady supply of hot water when you need it.
Recirculating pumps are used with tank-style central water heaters. They are not recommended to work with tankless models.
Recirculating pumps function in a variety of ways:
• A system that places the pump under the sink at the fixture farthest from the main water heater. The pump
is activated by a thermosensor and controlled by the user with a mechanical timer preventing it from
operating when not needed. This pump requires a power source near the pump usually in the form of a 120
• The most popular pump is one that mounts to the hot water outlet of the water heater and pushes hot water
into the system. The temperature is controlled by a non-powered thermostatic valve mounted under the sink
farthest from the main water heater. There is no water waste with this pump, which also minimizes energy
waste because it only sends hot water into the water supply lines during the programmed times. For homes
with multiple loops, you can purchase an extra bypass valve for each loop and use just one pump unit.
Installation is possible in under an hour.
Installation can be a do it yourself project, depending on the recirculating pump you select. Some models may require additional electrical work.
Features to Consider
Relief Valve – A relief valve is a safety mechanism that releases water (and pressure) if the temperature or pressure in the tank gets too high. During the installation, make sure you have allowed for a drain line from the relief valve. In the event relief valve should open, the discharged water should be carried away via a drain pipe.
Water Connections – Connections will vary depending on the capacity of the tank. Check to make sure you have the proper connection hoses before installation. Typically, 2 ½ gallon models will require a ½” water connection. Larger models will have a ¾” water connection.