Tankless heaters don’t have hot water storage. They make hot water on demand. This means that after the hot water is generated, the water still has to travel to the last faucet. And that means emptying a supply line that can range from 25 feet to approximately 600 feet.

Without a hot water recirculation setup, this water would be dumped down the drain by the homeowner while waiting for 1 to 4 minutes for hot water to arrive. All this waiting adds up to a lot of wasted water. Government studies estimate the average waste to be 12,000 gallons per year per household with four taps. And it can add up to 15,000 gallons for a very large home with more than five faucets in use.

Therefore, hot water recirculation for tankless heaters is essential since it saves water, utility fees and provides instant hot water comfort. 

AquaMotion was awarded a patent in 2020 for a water delivery system for tankless heaters. A circulator is installed near the tankless heater. The pump is installed in the hot outlet of the heater. The pump has a special connection with a built-in check and a flow control to deliver 1 GPM into the cold inlet of the heater through a special tee with a check to prevent hot water from entering the cold supply to the fixtures.

The heater control senses the return flow. It then fires until it senses the returning hot water. The heater will not fire again until the returning water cools.

In order not to waste the water down the drain while waiting for hot water, an ODR stainless Superflow bypass valve is installed undersink at the faucet furthest from the tankless heater, which allows a small amount of flow through it. This valve bypasses lukewarm water back into the cold supply line and back to the heater. The valve maintains 95 degrees at the faucet. The kit AMH1K-6ODRZT1 enables the tankless heater to deliver hot water faster and without short cycling, which could shorten the life of the tankless water heater.

Dedicated return lines

In dedicated return line systems, each tankless manufacturer has its own control parameters. The heater control may cycle the built-in or external pump at specific intervals to create flow. The heater control then checks the returning water temperature and only continues firing until the returning temperature is 15 degrees below the set point. This set up prevents short cycling and extends heater life.

Pumps with built-in timer generally have 48 tabs of 15 minutes run time increments when in TIMER mode. An ON and OFF switch provides for 24/7 runtime or vacation shutoff.

ON-DEMAND kits are available without a built-in timer on the pump. Instead, they offer a wireless push button communicating with a wireless receiver. When the homeowner calls for hot water, the pump will run for 5 minutes. The AMK-ODR by-pass valve kit installs under-sink. This kit can handle 600 feet of pipe and meets title 24 CA Code.

Another solution for a 600-foot pipe system is an undersink kit with all the components, a three speed stainless pump with timer, built-in Aquastat, 10-foot line cord, checks, hoses and special tees to meet title 24 CA Codes. This kit works for tankless heaters and large tanks installations.

For dedicated return line systems, the three-speed stainless pump with Aquastat, timer, flanges, checks and 10-foot line cord installs into the return line and meets title 24 CA Codes. 

Outdoor installations                                                                                                        

In the Southern portion of the county, tankless heaters are installed outside and attached to the home. This eliminates the expensive air intake and exhaust systems. AquaMotion developed AQUA-SHIELD, the first outdoor patent pending circulator, which installs near the tankless heater that is supplied without a built-in pump for dedicated return line system. Kits are available for 600-foot systems with a high speed flanged stainless circulator and a performance of 21 feet x 16 GPM.

Outdoor tankless systems with a pipe length of 250-foot pipe include a stainless union connection circulator with performance of 11 feet x 14 GPM. Both feature an outdoor enclosure to protect the pump from the elements and insects. The operating range is adjusted to the outdoor temperature and has an operating range of 115-125 degrees. The pump has built-in freeze protection for occasional cold spells when outdoor temperature drop below 40 degrees.

Single pipe outdoor tankless systems with on demand, features a wireless Call Button with wireless receiver. It also uses the ODR under-sink bypass valve and meets title 24 CA Codes. The flanged high-speed pump can handle 600 feet of total pipe length. A union circulator will work with smaller 250–foot systems.

Another outdoor single pipe kit offers the pump with a bypass to the cold inlet to the heater and the ODR under-sink bypass valve. All necessary components are included. 

These products help maintain the life of the tankless heaters and provide efficient hot water recirculation. They have resolved the issues with recirculation for tankless heaters. The pumps offer the patented replaceable and flushable cartridge with all stainless components. They can double the life of the pump and are, therefore, sustainable and green. All are UL and NSF372 listed and manufactured in Rhode Island by AquaMotion. Nine Patents cover the product line. Additional information is available at www.AquaMotionHVAC.com or info@AquaMotionHVAC.com.

About the author: Hans Kuster is an entrepreneur and inventor with 50 years of experience in the hydronics industry. He is the founder and president of AquaMotion and Sparco, sold to Honeywell in 2000, and has received 25 patents between the two companies.