What is a secondary return in plumbing?

Are you sick of having to wait for your hot water after you turn on the tap? Try installing something called a secondary return in your plumbing and wait no longer. The problem is that hot water rises and cold water sinks, letting cold water flow into both the water heater and down the drain, wasting water and increasing your utility bills. By installing a secondary return pipe from the farthest point in your hot water system back to your water heater you’ll save money, reduce your carbon footprint, and have instant hot water throughout your home.

How it works

When water is heated, it expands and becomes lighter; therefore it floats on top of denser colder water. With the tap closed, you only have half a circuit, with the colder water at the bottom nearest the outlet. However, when you open the tap, you complete the circuit – with the drain as the water’s destination. By installing a copper pipe leading back from the farthest point in the circuit to the heater, you create a secondary circuit, allowing water to circulate while the tap is closed, thereby making gravity to do the work.

Non-gravity plumbing

Gravity won’t work if your water heater is mounted in the basement. If that’s the case, install a small recirculating pump somewhere close to the water heater. Turn off the household water shut-off valve, open a hot water tap and drain the heater tank. Remove two inches of pipe, install a push-fit T coupling between the two halves and connect your pump to the open leg of the T coupling. Although small recirculating pumps don’t move a great deal of water, they are ideal for this type of application.


Use push-fit T couplings to connect the loop to your hot water outlet pipe as close to the point of use as possible. Connect the other end of the loop to the lowest point on your heater between the hot water drain valve and the tank. This may involve some creative plumbing, but avoid the use of solder and adhesives by using push-fit T couplings available from plumbing outlets dealing with PEX piping.

Check valve

Install a check valve – sometimes called a non-return valve – between the end of the secondary return and the hot water heater. This will stop cold water flowing backwards into the circuit from the bottom of the water heater when you open a hot water outlet anywhere in your home.

Water hammer

To prevent trapped air causing water hammer (that juddering sound you sometimes get when you turn the tap on) in your secondary return, install a vertically oriented water hammer arrester in the loop as close to the inlet point as possible. Water hammer arresters contain a spring-loaded gas-charged piston above the water line, designed to absorb hydraulic shock caused by air infiltrating the secondary return.

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About the Author

After graduating from the University of the Witwatersrand and qualifying as an aircraft engineer, Ian Kelly joined a Kitchen remodeling company and qualified as a Certified Kitchen Designer (CKD). Kelly then established an organization specializing in home improvement, including repair and maintenance of household appliances, garden equipment and lawn mowers.