Hot water recirculation: pumps, loops and controls

How does a hot water recirculation system work?

In a standard house the hot pipe is a dead end. Once the tap is closed, the water in the pipe cools down, and the next person to open it runs the tap until the warm water arrives from the heater. A recirculation system sends the cooled water back to the water heater, so the pipe stays near temperature.

There are two layouts. A dedicated return line runs from the farthest fixture back to the heater, and a small pump circulates the water through the loop. A retrofit version uses a pump and a crossover valve at the last fixture to push cooled hot water back through the cold line, so no new pipe is needed. The cold tap then briefly delivers warm water, which some households notice.

What controls decide the energy use?

A pump that runs all day keeps the pipe hot and loses heat to the walls the whole time. Four control methods limit that.

• Timer. Runs the pump at set periods, such as the morning and evening peaks.
• Temperature control. Stops the pump once the return water reaches a set temperature.
• On-demand push button or sensor. Starts the pump only when someone asks for hot water.
• Learning controls. Adjust run times to the household's pattern.

On-demand control is generally the most frugal, because the pipe is warm only when someone is about to use it. Check what the unit you are considering offers. Fittings and pipe insulation matter too, and the guide to lowering your heating bill in winter covers other places a house loses heat.

Is a recirculation pump worth it?

The honest answer depends on the house. In a compact home with the heater close to the bathrooms, the wait is short and a pump rarely pays. In a large or long-run house, where the far tap takes a minute or more to turn warm, the pump saves water and avoids the annoyance. Water savings count most where supply is metered or limited, such as on a well or a cistern.

A permanently running loop can raise the water heating bill, so controls and pipe insulation are not optional extras. Insulating the hot pipes, including the return, is a low-cost step that helps with or without a pump. Ask an installer to estimate the electricity use of the pump and the extra heat load on your heater, then compare it to the water saved.

Does recirculation work with every water heater?

Not equally. Storage tanks accept a return line easily, though a loop can keep the lower part of the tank warm and reduce stratification, which matters for some designs. Gas tankless units often need a unit rated for recirculation or a small buffer tank, because the cycling is not what they were built for. Heat pump water heaters work best with a controlled loop, since a hot return raises tank temperature and lowers efficiency. Read heat pump water heaters in Canada and tank versus tankless before specifying one.

A larger tank sized for peak use changes the picture too, and hot water tank sizing explains how. Solar preheat systems add another stage, covered in solar hot water cost in Canada. At Drake Landing Solar Community the heat circulated through a district loop to each home, which is a different problem from a household hot water line. See how it worked on the district heating page.

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