How Does a Gravity Hot Water Recirculation Loop Work? How Does a Gravity Hot Water Recirculation Loop Work?

A gravity hot water recirculation loop works by allowing the laws of nature to come into play. Hot water tends to rise while cold water tends to descend at the bottom of a contained space. If you are in a swimming pool, you will notice that the temperature of the water becomes colder as you go deeper in the pool.

Simple hot water piping systems are designed to terminate at the farthest fixture. When you turn on a tap, the water heater is activated and hot water is generated after a few minutes. In this type of system, water is wasted when you wait for hot water to flow out of a tap. Inconvenience is also another consideration as hot water is not quickly available.

Installing a Gravity Hot Water Recirculation Loop

One way of addressing the issue of a long wait, for hot water in taps, is to install a gravity hot water recirculation loop. With a recirculation loop, hot water circulates continuously through the piping line while aided by the forces of gravity. Hot water from the heater rises to the pipes, while cold water moves towards the heater.

In a recirculation loop, a return line that runs from the farthest fixture back to the water heater is installed. The return line winds its way down to the bottom of the water heater where the drain valve is connected.

But for the system to work efficiently, the entire supply line connecting the water heater to the taps should be insulated to reduce or eliminate heat loss when hot water is flowing through the pipes. Additionally, the return lines should also be insulated except for the last 15 feet. This way, the water in the last stretch of the system will lose heat and flow easily back to the heater.  You can either wrap the lines with foam insulation, or install pipes that have built in insulation; e.g. fiberglass insulation. The former is easier to install.

When putting the recirculation loop in place, make sure to turn off the water heater’s power supply. Drain the water heater and remove the drain valve by turning it counter clockwise until it comes off. Put an insulating nipple valve or dielectric union in place of the valve to prevent corrosion—especially if you will be using galvanized iron or copper pipes. The recommended size for the main supply and return pipes is ¾ inches.

It is recommended that recirculation loops be installed during the building phase of a house or building, to ensure efficiency in the plumbing design. The system also works best in multi-level houses or facilities, where the water heater is located at the bottom of the piping system.

Seeking the advice of an experienced plumber when installing a recirculation loop will also be very helpful. 

The Benefits You Get

It can be argued that energy consumption will be higher in a recirculation system; however, the costs can be offset by the savings you would get from lesser water wastage.  


Generally speaking, facilities and homes located in areas where water is in short supply would benefit tremendously from recirculation loop systems.

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