'Feedback' loop on thermostatic mixing valve.

nibs

If we put a loop from the DHW line just before the mixing valve, to send any excess HW back to the tankless water heater cold intake, will that give me a net increase in volume of HW by decreasing the delta T for the heater?

Jamie Hall

Problem: if there is no pump on the tankless -- and I doubt that there is -- the head loss through the tankless will be greater than that through the loop. So... what will happen is that water will flow from the cold water connection through the loop in greater quantity (for a given flow rate) out of the mixing valve than it will through the tankless. So... no joy. There is no arrangement -- short of a pump -- which will cause recirculation and a reduction in delta T.

nibs

@Jamie Hall After hanging out here for the last year, I should have figured that out for m'self.
Read your explanation and thought "what about a check valve?"
Then thought it through, Thank you sir for yet another lesson.