Rheem Marathon 85 gal and Taco Recirculator - A pig!

I wish I could put this in “Device Detection” to show you the clean signature, but after two months the water heater has not been detected. The house is not occupied yet so we are in shakedown cruise mode. I was very interested to see the electricity use with and without the recirculator pump going.

With the pump running constantly, the water heater turns on 5 minutes out of every 15. It has a 3800 watt element so this dumb human can easily recognize the signature (ahem). Once I turned the pump off the heater came on for 5 minutes every half hour. Still a lot for a zero water demand situation, IMHO. At $0.10/kwh, it works out to $555/year with NO use…

Rheem advertises in their product brochure that the temperature drops only 5 deg. F in 24 hours when in “standby.” I cut the power and the temperature dropped from 133 to 104 in 24 hours, nearly 30 deg. Hmmmm.

At a minimum I will put some smarts on the recirculator, which my plumber did not feel the need to do.

It’s possible your recirculation loop is moving water even with the pump turned off due to convective circulation. Those pumps use a centrifugal design, so water can flow through them easily even if the motor is off. This flow could be causing the standby losses.

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Interesting idea. Seem non-intuitive. If I just pulled the pump out of the line the water would behave the same, right? There’s quite a few feet of pipe to push water through.

Yes, here are some more details on this concept:

Depends on the loop design whether it will work. In many cases it will.

Cool! Thanks.

I put my circulating pump on a “smart plug”. I use the command “OK Google, turn on the hot water for 1.5 minutes”. This way I don’t forget to turn off the pump. I also have a second smart plug with a large night light that is paired with the circulating pump. I can tell at a glance from the kitchen when the pump is turned on.

I used a motion sensor in their master to turn on the recirculating pump for my parents. It shuts off again after a few mins. They have a real loop, I have a retrofit loop with crossover valves, the valves shut off automatically at 90 deg, I think.

I’m testing a home loop system with a combo tankless, and hybrid Raheem. I wanted to see the the total cost of heating my water, and how much hot water I really use.

I installed a StreamLabs flow meter on my outgoing hot water line. The crossover valves definitely close as expected and flow stops until someone open the tap.

You could add the same flow meter to troubleshoot the issue which requires no plumbing and seems to work well.