Possible to get truly instant hot using a crossover?

[Sonny goldstone]

Hello...

Is it possible to get instant hot water using a crossover valve rather than dedicated return?

I have a crossover valve setup and the performance isn’t great - I’m wondering if it’s possible to get “instant hot”( eg 120 degrees in 10 seconds) with a crossover rather than a dedicated return

thanks

 

[Fitter30]

The more the pump runs the warmer the hot water will be but also the cold water becuse that where all the warm water is going. 2.5 gpm faucet 10 seconds .41 gallon.

 

[Sponsor]

 

[Jadnashua]

From what I've read, most of the cross-overs close at around 105-degrees, so hotter is close, but not there.

You could probably make your own cross-over at set it to a higher temperature, but your cold line will become the same temperature, and you probably won't like it! The only way around that is a dedicated return line.

If it was only one location, you could put a small, say 5g electric tank there, fed with the hot water line. By the time hot got to the tank, the mix with the existing hot in the small tank would likely let you keep the outlet high.

 

[Bannerman]

most of the cross-overs close at around 105-degrees,

Except, in this case, the crossover chosen will close at 95F as has been previously discussed in this poster's other threads.

 

[Sonny goldstone]

Except, in this case, the crossover chosen will close at 95F as has been previously discussed in this poster's other threads.

Yes it does close at 95 - what I don’t understand is that even if it closes at 95, wouldn’t the hot side continue to heat up as 120 degree water is pushed into the line?

 

[Bannerman]

Once circulation is stopped at the crossover valve, the pump cannot push additional water into the line. Water is not compressible so although the pump may continue to run, with nowhere for the water to flow to, the pump will spin with no flow resulting, similar to a vehicle not moving while the tires are spinning on ice.

With no water flow, the tankless gas burner will shut down otherwise, water within the heat exchanger will quickly become superheated to steam.

 

[Sonny goldstone]

Once circulation is stopped at the crossover valve, the pump cannot push additional water into the line.. Water is not compressible so although the pump may continue to run, with nowhere for the water to flow to, the pump will spin with no flow resulting, similar to a vehicle not moving while the tires are spinning on ice..

With no water flow, the tankless gas burner will shut down otherwise, water within the heat exchanger will be quickly become superheated to steam.

I got it - based on this description I don’t see how water could get “instantly” hotter than the crossover cutoff temp - maybe the answer is a higher temp crossover - thanks!

 

[Bannerman]

maybe the answer is a higher temp crossover

As mentioned above, the usual upper limit for a crossover is ~105℉. Although 10° hotter than with your current valve, it remains well below the 120℉ you are wanting and expecting.

Because your home's cold water lines are providing the return path back to the WH, if the crossover valve shutoff temperature is 10° hotter, then the 'Cold' water will be also 10° hotter.

As stated in your other thread, using the cold water lines for return flow is somewhat of a hack or kluge so recirculation can be added to a home not equipped for that capability. Although it will not provide instant hot water, tepid water will arrive more quickly so there will be less water waste in clearing cold water from the line while waiting for hot water to arrive.

Because hot water in cold lines will usually cause other problems such as brushing teeth with hot or temperature regulation issues through shower control valves, the temperature entering the cold lines will need to be restricted. Such restrictions are not necessary when a dedicated return line is used so recirculation can be constant, resulting in more immediate hotter water at faucets.

 

[Sonny goldstone]

As mentioned above, the usual upper limit for a crossover is ~105℉. Although 10° hotter than with your current valve, it remains well below the 120℉ you are wanting and expecting.

Because your home's cold water lines are providing the return path back to the WH, if the crossover valve shutoff temperature is 10° hotter, then the 'Cold' water will be also 10° hotter.

As stated in your other thread, using the cold water lines for return flow is somewhat of a hack or kluge so recirculation can be added to a home not equipped for that capability. Although it will not provide instant hot water, tepid water will arrive more quickly so there will be less water waste in clearing cold water from the line while waiting for hot water to arrive.

Because hot water in cold lines will usually cause other problems such as brushing teeth with hot or temperature regulation issues through shower control valves, the temperature entering the cold lines will need to be restricted. Such restrictions are not necessary when a dedicated return line is used so recirculation can be constant, resulting in more immediate hotter water at faucets.

I got it now - I wouldn’t mind an extra 10 degrees but not sure if I can just swap in any crossover or if it needs to be the one that came with the Noritz kit

 

[vicycleseven]

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