Hot water recirculation technology is improving and becoming more popular in new builds.
For years hot water circulation systems, including pumps and return lines, have been sold as a powerful water conservation solution, some estimates reporting the systems can save as much as 1,000 gallons of water per person annually. For a family of four, that’s about 50 bathtubs full of water every year that’s saved from going down the drain. multistage pump
It’s for this reason some water-starved jurisdictions, like California, have placed hot water recirculation in the code, ensuring homeowners have no reason for letting the water run while waiting for it to get hot.
Hot water recirculation has been standard in large multi-unit residential apartment and condo buildings for decades, as it can take minutes for water to travel between water heaters in mechanical rooms and occupied units. Also, the constant movement keeps the warm water in the building’s pipes from stagnating, avoiding the possibility of Legionella bacteria forming.
The installation of dedicated hot water recirc lines in single-family homes across Canada has been available for many years as well, but the demand for the convenience seems to be growing.
“We’re seeing more builders are supplying it as standard, at least out here in Alberta,” says Bruce Layte, district sales manager with Grundfos Canada. He’s seeing hot water recirc in show homes in new developments, and in larger higher-end new builds where the owners seem to be more conscious of water and energy savings.
Steve Goldie, HPAC plumbing columnist who works with Ontario-based plumbing and hydronics wholesaler Next Supply, recalls hot water recirc being a luxury back when he was on the tools over 20 years ago. “It was an option back then, but one that more and more people today think is necessary. People want to turn the tap on and have hot water there right now, and it saves water, so there is an ecological reason for doing it.”
In its simplest form, a hot water recirculation system keeps hot water flowing and accessible in the hot water lines.
In new construction the hot water supply line from the water heater will branch off to each fixture in the home, and then a dedicated return line is run from the furthest fixture in the house back to the water heater. It’s on this dedicated return line (where it connects back to the water heater in the mechanical room) that a hot water recirc pump will be located.
In the case of a gas or electric fired tank water heater, the recirc pump will often be attached to the boiler drain located at the bottom of a water heater tank. Contractors will place a tee in that position and put the drain valve on one side of the tee and the hot water recirc will port on the other.
“We also see the return line coming back and teeing into the cold water line which is going back into the tank,” says Layte. “Now you have to put a check valve in there as well so that cold water doesn’t go back through the pump.”
Recirc pumps can also be attached to tankless water heaters, and now many of today’s tankless water heater manufacturers are offering models with recirc pumps built in that can be adapted to work with a dedicated recirc return line or with a retrofit system.
For homes without a dedicated recirc line installed, the modern retrofit solution involves placing a four-way bypass valve at the fixture which is furthest away from the water heater.
Placed under a sink for example, the simple valve will connect to both the hot and cold water lines on either end, and between the hot and cold side is a temperature sensing bypass valve that will open when the water is cool and close when it’s hot.
When the valve opens, a recirc pump located on the hot water supply side of the water heater, or in some cases under the sink and plugged into an outlet, will send water through the line, and the return water will be delivered back to the water heater through the home’s cold water line. Once the temperature at that four-way valve is hot enough the valve will close.
“With this system, yes you now get hot water instantly, but you also get warm or temperate water in the cold water line,” notes Goldie. “So, if you want cold water to get a drink or brush your teeth, then you end up running the cold water line to purge the tempered water out. So it’s a compromise.”
As noted, recirculation systems have been in large buildings for years, and traditionally they operate oversized recirc pumps that run continuously 24/7. As a result, for the convenience of instant hot water there is a lot of energy lost through the constant running of the pump along with the standing heat loss in the piping circuit.
Benoit Maneckjee, the founder of ThermAtlantic Energy Products in Newfoundland, has installed systems in many multi-unit residential buildings and notes that sometimes the hot water recirc load represents 25 to 30% of the entire energy of the building if it’s not designed properly.
Goldie recalls having his eyes opened to massive energy loss through a recirc line at an estate home in Toronto. The mansion had four 120-gallon indirect tanks for hot water and over a million Btus of boiler capacity.
“Well, one evening the boilers locked out on some fault at two o’clock in the morning. The owner gets up early around 6 a.m. and goes for a shower and there’s no hot water,” says Goldie.
Called in by the contractor, together they were able to figure out the boiler lock-out issue (a faulty component), but how did the homeowners run out of hot water with all of that storage?
“We’re looking around and discovered a recirc line going through this pipe chase area that led underground to a sink in an outdoor greenhouse. That half-inch recirc line was running 24/7.” Because of the cold outside temperature, he assumes the line used all the hot water capacity in four hours.
“It was mind boggling. This was an extreme situation, but I would never have guessed that would have been the cause.”
One solution to assist with standing heat loss is to insulate all the hot water piping. “Insulation is still neglected too often,” says Goldie. “It’s best practice, but it often doesn’t get done so there’s massive energy loss there that nobody talks about or really tracks.”
In addition to heat loss through the piping, with water constantly feeding back to the water heater, gas or electricity is being used to reheat that water.
The solution is better controls on hot water recirculation that can lead to much improved energy efficiency.
Today’s hot water recirculation systems employ a number of control strategies to mitigate potential heat loss issues, control flow and keep the pumps from constantly running.
Using a timing control is one way to conserve energy. One method Maneckjee has used in multi-unit residential buildings is to put the recirc pump on a 10-minute duty cycle where the pump runs for 2.5 minutes then it goes off for 7.5 minutes.
“This drastically reduces the amount of energy wasted by the recirculation system,” he says. “This way we ensure everyone will have hot water when they need it (it’s not going to cool off in 7.5 minutes), but we save a tremendous amount of heat loss. We were able to reduce the loss by two thirds while still maintaining hot water in the building.”
In residential homes, timer controls and temperature controls using aquastats is the way recirc pump manufacturers have been managing usage. Some pumps plug into an outlet, and they may have a timer at the outlet to turn the power on or off. Some pumps are outfitted with timers attached to them with switches turning on and off at set times based on when the hot water is being used the most.
Some timer set ups can also monitor usage patterns and then the pump will operate during those time periods. If the hot water isn’t used for over 24 hours, some systems will shut down completely (making the assumption that the occupants are on vacation).
Aquastat sensors are used by some pumps (sometimes together with timer controls), and when the temperature of the water in the dedicated return line drops below a certain set-point the pump turns on until the temperature in the line reaches an upper set point (if the timer is set up as well, it will override and only turn on during the set times).
Another control strategy is an on-demand system, where the homeowner can actually push a button, or a motion sensor can be activated, to call for the recirc system to turn on. In some jurisdictions, like California, this control option is a requirement.
With modern energy efficient electronically commutated motors (ECMs) and onboard digital controls, today’s recirculating pumps have the built-in intelligence to optimize residential recirc system operations.
Taco introduced its 006e3 ECM hot water circulation pump in 2018, a low-energy pump that pairs with other solutions to work with dedicated return lines or retrofit systems.
This year at the 2024 AHR Expo in Chicago, Grundfos introduced its Alpha HWR pump for recirc systems with a dedicated line, and the Alpha Comfort System for retrofit applications. These ECM pumps are available with integrated timer and temperature sensors as well as flow velocity control.
A common issue with hot water recirc in buildings is oversized pumps pushing high flow rates through the pipes leading to pinhole leaks. It’s seen in the copper risers of large multi-unit buildings and can also occur in PEX piping as the combination of heat and chlorine in the water along with high flow can contribute to breaking down a PEX pipe’s structure.
Pinholes in copper tubing and PEX can be caused by constant high flow rates. (photo: Digical/Getty Images)
Uponor recommends a maximum velocity of 2-ft./second for the common pipe sizes of ½-in., ¾-in. and 1-in., which equates to flow rates of 1.1-, 2.2- and 3.6-gpm respectively.
“When you size a recirc pump you should be sizing for these flow rates,” says Layte.
In any retrofit recirc system operating with a pump that is on 24/7 or on a timer, that four-way valve at the furthest fixture could be opening and closing at different times throughout the day, but the pump will continue running. So, when the valve is closed, that pump will be deadheading and wasting energy. The new ECM pump can provide a solution for the issue of deadheading.
“With our new smart pump for the retrofit recirc, the Alpha Comfort System, the pump will actually shut down when that valve closes,” says Layte. “Because it’s an ECM smart pump it monitors the power consumption, so there is a signature when that valve closes, there’s low power consumption, and the pump says, ‘OK that valve must be closed, I’m going to shut down.’”
The ECM technology also allows today’s pumps to gradually ramp up and ramp down, avoiding any sudden bursts of hot water at a fixture when the system starts up.
The ECM Alpha HWR pump from Grundfos has integrated controls that can be set up and adjusted remotely by an app. (source: Grundfos)
In addition to the digital controls built into the modern pumps, the connectivity is extended through Bluetooth capabilities. Contractors can access the pump’s settings remotely to optimize its operations and view real time data as well as historical performance.
An app can also allow the home owner to adjust settings like timing and temperature to their own preference from their phone.
So, are hot water recirculation lines a luxury or a necessity?
Well, yes to both may be the right answer!
In large homes, where it can take minutes for hot water to reach showers and faucets, hot water recirculation systems installed correctly with insulation and with optimized control strategies to conserve both water consumption and energy just makes sense.
priming water pump If it can be done, why don’t we. And of course, not having to endure the chill of waiting for the shower water to heat up is a perk, and as the trend of hot water recirc catches on it’s a luxury that everyone should enjoy. <>