I have a Rinnai tankless water heater (flow-activated). Can I use a closed loop circulating system on hot water line downstream of Rinnai?

Asked by Tom Stivers
Frankford, DE

The goal is to minimize the cold water flow when the hot water spigot is opened. It seems to me that the water circulating in the hot water closed loop will not activate the Rinnai until a hot water spigot is opened. I would think I would need a check valve between the Rinnai and the loop. The problem is I'm just not sure how much water I save with this arrangement.


Raymond Pruban

Answered by Raymond Pruban

Woodbury, MN

Amaris Custom Homes

December 29, 2010

You can have a recirculating pump on a tankless, but you need to purchase a recirculating pump that will actually activate the tankless heater.

  • Check with the tankless manufacturer.
  • I have also heard that some tankless manufacturers are voiding warranties when a recirculating pump is connected, so you need to verify. Rinnai might be one of those companies.

It would defeat the purpose to have the recirculating pump running 24/7, so please make sure you install a recirculating pump that is on a timer or on a point-of-use switch. The timer would run the pump for one or two hours in the morning for showers. The point-of-use switch can be turned on a few minutes before a shower and turned off after the shower.

I have been installing Rinnais for a few years and feel the recirculating pump is worth the effort, but I do not have any hard numbers.

Tagged In: tankless, hot water recirculating

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