Can demand recirculation pumps alleviate the tankless "cold water sandwich"?

[nz_WI]

Hi, I'm a student in the process of designing a plumbing system. I'm aiming for energy efficiency, and tankless water heaters are supposed to be much more efficient than storage heaters due to the fact they only start when water is flowing. However, one of their drawbacks is that it takes a while for them to bring water up to temperature, leaving the risk of a "cold water sandwich" between the sitting water in the pipes and the soon-to-be-heated water.

What I'd like to know is, would a demand recirculation pump alleviate this? What I envision is that as a person walks into the bathroom, the pump is activated, which in turn activates the tankless heater. Assuming the recirculation loop is short enough, the cold water spot is moved very near to or past the fixture. Does this seem feasible, and has anyone ever installed or encountered something like this? Any other tips to make a tankless water heater work correctly? Or should I just ditch them?

 

[Mr_David]

Did you try a typical search for items available already designed for this application. here are 3 links .

Try this in your favorite search engine

recirculating hot water system with tankless hot water heater


LINK #1

LINK #2

LINK #3

 

[nz_WI]

Did you try a typical search for items available already designed for this application. here are 3 links .

Try this in your favorite search engine

recirculating hot water system with tankless hot water heater


LINK #1

LINK #2

LINK #3

Thanks for the quick reply. I guess I should rephrase my question: I'm aware that it's possible to use a demand recirculation pump with a tankless, but I'm wondering if it actually works in practice to minimize hot water time, and if anyone can attest to its effectiveness in the field. Common complaints are that it takes too long for hot water to arrive and that there is a burst of cold water from the pipes, and I'm wondering if anyone here solved that by putting in a recirculation pump.

 

[havasu]

If you purchased a Navien tankless water heater, it comes with a built in buffer tank AND a recirculating pump. No cold water at all when you want hot water.