Crossover recirculation?

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D. Shelston

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I'm new with a tankless and not happy with the wasted water and time to get hot water at the shower head...

My tankless has a built-in recirculating pump but only to be used with a dedicated return line. I do not have return lines.

Guess I need to install another external pump on the hot side, near the outlet and a crossover gizmo at the furthest faucet. Would this work? One question I have is, if the pump runs constantly, what happens when the temp has been reached and the crossover closes...

Thank you.
 

WorthFlorida

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There are kits out there and some run on a timer (less costly) when to turn on the circulator pump at certain time intervals. Smart units (more costly) use a water flow sensor and temperature sensor. You want the one using the cold water pipe as a return.
https://readytemp.com/
 

Bannerman

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not happy with the wasted water and time to get hot water at the shower head...
That situation is not unique to tankless as the same situation will occur with a conventional tank-type WH. The pipe diameter and distance between the WH & fixture will determine the time and quantity of cool water needing to be eliminated before hot water will arrive at each fixture.

My tankless has a built-in recirculating pump but only to be used with a dedicated return line.
The existing internal pump may be able to be utilized depending on the pump configuration in relation to the loop return line connection.

You didn't mention the brand and model of your tankless unit but Navien units equipped with an internal pump allow utilizing either the home's cold water lines or a dedicated return line for circulation.
 

Fitter30

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Every brand of condensing waters heaters have their own recommended recirculation methods. Need brand and model number if you don't have the install manual. Manuals are on the internet. Some use a push button, occupied sensor to turn heater on.
 

wwhitney

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That situation is not unique to tankless as the same situation will occur with a conventional tank-type WH. The pipe diameter and distance between the WH & fixture will determine the time and quantity of cool water needing to be eliminated before hot water will arrive at each fixture.
Right, but it is exacerbated by a tankless heater because (a) there's no tank of hot water to partially warm the water in the pipes by thermosiphon or conduction and (b) the burner does have a non-zero delay for activation and warming on when the hot water draw starts (maybe a few seconds).

Cheers, Wayne
 

Bannerman

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Navien models equipped with an internal circulator pump do incorporate a small internal buffer tank to assist to prevent the 'hot water sandwich' effect which is common with tankless units without a buffer tank. This commonly occurs when a hot water faucet is run, shut off and turned on again within a short time period before the hot water within the pipes have cooled.

The OP has not stated his tankless brand or model but only mentioned concern with the time required and the quantity of water wasted while waiting for hot water to arrive to his shower.

Perhaps he does not own a Navien brand tankless but obtained an alternate brand that does not offer its own thermostat crossover valve which maybe why only a dedicated return line was specified in the installation manual.
 
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D. Shelston

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My tankless is from an Italian company, Radiant Model SFK 55.

https://radianthydronics.com/

The recirculation pump only works with a dedicated return line which I don't have. New home, installed by the builder, basement fully finished.

Trying to figure out if I could get hot water faster to the shower head by using a Crossover at the furthest faucet with an external pump....

I should add I'm in Canada and in our little town water and sewer is incredibly expensive. $150 each month is normal....
 
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D. Shelston

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Here are some schematics.
 

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D. Shelston

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Heres the install manual show a return line for recirculation.
[PDF] SFK 55 - Radiant Hydronics
radianthydronics.com › 2016/12
I know, and I mentioned it....

I cannot add a recirculation line, my basement is fully finished.

Just asking if a Crossover valve at the furthest faucet would work or help...
 

Bannerman

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asking if a Crossover valve at the furthest faucet would work
A crossover valve located at the greatest distance should help hot water to arrive faster to all hot faucets along the path.

Since the cold water plumbing will be acting as the return path back to the water heater, you will usually not want the cold water to become very warm. Most crossover valves incorporate a thermostatic valve which will stop the return flow once a specific temperature is achieved. The shutoff temp varies somewhat by brand.

As an example, Navien NaviCirc will stop return flow once sensing 95 degrees. As such, the 'cold' water just past the crossover valve may have risen as high as 90-95, but people that use them report the warm water within the cold line will typically be quickly eliminated once the toilet is flush or while initially turning on the shower prior to entering.

Although the hot water temp at the faucet where the crossover valve is located will be only 95 degrees almost immediately, the water temperature will quickly rise to the full temperature as hotter water is already nearby.

Any faucets which are fed by a line which already contains hot water flowing to the crossover valve will also receive hot water faster than previously, even as a crossover valve may not be installed at that location.
 

D. Shelston

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A crossover valve located at the greatest distance should help hot water to arrive faster to all hot faucets along the path.

Since the cold water plumbing will be acting as the return path back to the water heater, you will usually not want the cold water to become very warm. Most crossover valves incorporate a thermostatic valve which will stop the return flow once a specific temperature is achieved. The shutoff temp varies somewhat by brand.

As an example, Navien NaviCirc will stop return flow once sensing 95 degrees. As such, the 'cold' water just past the crossover valve may have risen as high as 90-95, but people that use them report the warm water within the cold line will typically be quickly eliminated once the toilet is flush or while initially turning on the shower prior to entering.

Although the hot water temp at the faucet where the crossover valve is located will be only 95 degrees almost immediately, the water temperature will quickly rise to the full temperature as hotter water is already nearby.

Any faucets which are fed by a line which already contains hot water flowing to the crossover valve will also receive hot water faster than previously, even as a crossover valve may not be installed at that location.
Thank you so much. That is the information I was looking for.

I'll be using the one by Watts, the temperature setting is not published as far as I can see. But that's OK. If. Guess it's got to be pretty close to the one from Navien.

Again, thank you.
 
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