Check valve for gravity hot water re-circulation

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bhoth

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Ok the move from the first WH to the 2nd is complete, I do not have have any way of checking temperature before or after this move.

See below:
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bhoth

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Well the move seems to have resolved the issue of cold mixing with the hot. The hot water in the shower this morning stayed consistent.

Thank you so much for all the comments that guided me along the way!

Still wondering why switching from the first HW to the second HW made such a difference, anyone have any ideas?

Thanks again!
 

Reach4

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Still wondering why switching from the first HW to the second HW made such a difference, anyone have any ideas?
I have 2 possible explainations:
  1. The recirculation flow may have increased keeping the water in both the hot supply pipe and the recirculation line warmer.
  2. The dip tube bottom of the units may have been near the bottom port. Any reverse flow could be sucking the colder water. With the current situation, the dip tube near the port in use is bringing in hot water from the first tank.
 

Widgit Maker

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More likely that the check valve is still not working as it should. Before the water moving up the recirculation line was the cold water coming in. Now the water moving up the recirculation line is coming from the bottom of the first tank, which is the hot water coming in from the second tank.
 

Reach4

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More likely that the check valve is still not working as it should. Before the water moving up the recirculation line was the cold water coming in. Now the water moving up the recirculation line is coming from the bottom of the first tank, which is the hot water coming in from the second tank.
That theory could be tested by turning off the first WH for a day.
 

bhoth

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That theory could be tested by turning off the first WH for a day.
I should also mention that the heat is set to Hot on the first WH and Very Hot on the second WH but this should NOT make a difference as long as the check valve is doing it's job.
26350130394_791da10f19_o.jpg
 

Widgit Maker

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But the check valve is not doing its job. If it were you would not have had to move the recirculation line. There is nothing wrong with this arrangement. You have your recirculation line and instant hot water at the point of use. You won't notice any temperature difference until you have used all the water in the first tank and about half the water in the second tank. Then you will notice a reduction in water temperature because the water coming from the second tank to the first tank will be warm not hot, because of the mix of cold water coming into the second tank.
 
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Jim123

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In my house there’s a three-quarter inch copper supply line for the upstairs hot water in the bathrooms. At the end of that run I teed off a ½ inch PEX line which runs about 60 feet back to the water heater two floors down in the basement. In the basement, the PEX connects to a shut off valve followed by a spigot followed by a one-way valve and then the whole thing ties into the cold water inlet about 18 inches above the water heater (see picture).

With this configuration I can connect a hose to the spigot and drain the air out of the system which is critical for the convection to work properly. When I first put the return line in I didn’t do a thorough job purging the air and the hot water convection didn’t start working for several weeks. Apparently it took that long for the air to work its way out of the system. Next time I drained the water in the house I did a better job purging the air and the convection loop started up quickly.

I can also close the valve and open the spigot to test that the one-way valve is working properly. The one-way valve prevents cold water from flowing back up the convection line when someone opens up the hot water upstairs. The one-way is a ball type with no spring and is available from Amazon (search on “pex check valve”).

Everyone in the house is thrilled to have warm water coming out immediately the faucets and showers upstairs. In fact the water is downright hot within a few seconds which is more than we really need. What I was after is for the water to not be cold so I’ve experimented with partially closing the valve in the basement to reduce the convection flow.

When I started I was skeptical that convection would be enough to circulate the water but figured I could add a pump if necessary. It appears that no pump is needed and I am very pleased with how the whole system works.
 

nomad297

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I realize I’m late to the game here, but I will give my advice, anyways.

I have been installing gravity circulation systems for close to four decades. The trick here is to install a standard swing check valve at 45 degrees (or somewhere else between horizontal and vertical) before the loop enters the bottom of the tank. This keeps the gate open to allow the convection to occur, then, when there is demand and flow tries to pull water out of the bottom of the tank, the gate closes keeping the water from the bottom of the tank drawing back into the loop.

With the installation of two water heaters in series, you must connect the loop to the first tank for it to be most effective since the water at the bottom of this tank is going to be colder than the water at the bottom of the second tank, making for a more effective convection due to the difference in temperature.

It’s also a great idea to insulate the entire loop. The branches aren’t so important.
 

Plumbserve

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I realize I’m late to the game here, but I will give my advice, anyways.

I have been installing gravity circulation systems for close to four decades. The trick here is to install a standard swing check valve at 45 degrees (or somewhere else between horizontal and vertical) before the loop enters the bottom of the tank. This keeps the gate open to allow the convection to occur, then, when there is demand and flow tries to pull water out of the bottom of the tank, the gate closes keeping the water from the bottom of the tank drawing back into the loop.

With the installation of two water heaters in series, you must connect the loop to the first tank for it to be most effective since the water at the bottom of this tank is going to be colder than the water at the bottom of the second tank, making for a more effective convection due to the difference in temperature.

It’s also a great idea to insulate the entire loop. The branches aren’t so important.
In my experience we have design a vertical check valve design with a negative buoyancy washer to balance the gravity circulation. We always install a flush valve for air in the lines but in design the vertical valve will purge the air with usage but takes several times before all air is flushed out completely. Check the heat traps on the water heater they can restrict flow. Check patent Grav-Flow design. This should help you with the cold pockets unless the line has a drip in the feed line, this slows and can even stop the thermo lift side of the therm o-siphon system.
 
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