Recirculating pump and thermostatic mixing valve - some questions

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JayEss

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Hi everyone,

I'm planning to add a recirculating pump on my hot water line, as it takes about a minute for the fixtures furthest away from the water heater to get hot water. I have a thermostatic mixing valve which I know makes things a little more complicated, but from my understanding it's still possible to add a recirculating pump as long as it's temperature-controlled so it doesn't run constantly. Some info about my home:
  • I have a dedicated return line for recirculation.
  • I have a Braukmann AMX300LF mixing valve, which has a dedicated inlet for recirculation.
Here's what my current setup looks like:

Water heater - existing configuration_setup.png


And here's how I'm planning to change it:

Water heater - recirculation configuration_setup.png


So now, onto my questions:
  1. Does this look right, or does anything need to be changed here?
  2. Should I be removing the check valve that's between the water heater and the mixing valve? All of the installation diagrams I've seen don't have a check valve there.
  3. My house is plumbed with PEX and the dedicated return line has a 1/2" copper stub-out. What's the "right" way to hook up the pump to that stub-out? From my understanding I don't want to sweat the copper stub-out since the heat can damage the PEX in the wall, so I was thinking I could use a compression x FIP fitting and an MIP x PEX barb and then just run PEX for the whole thing.
  4. I'm looking at a Grundfos 99412493 pump, which has a built-in temperature sensor so no aquastat is needed. According to Grundfos this pump runs for 10 minutes to determine the max temperature of the system, then automatically turns the pump on and off to keep the water temp 7-14 degrees Celsius lower than the max temperature that it previously detected. That 10-minute run to find the max temp repeats every 12 hours. Will that work correctly with a mixing valve, or would it be better to go with a more traditional system that uses an aquastat?
Thanks so much everyone! I've learned a ton from reading these forums over the years.
 

Jeff H Young

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I don't think this works . I don't see how hot water from tank can travel if no water is going back to the tank. check braukman specs. don't know how you came up with this plan but I'm thinking NO
 

JayEss

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What kind of water heater do you have? Why do you need the mixing valve?
Just a plain old natural gas, 50-gallon water heater (Bradford White in case it matters). I have a mixing valve to effectively give my house more hot water, as a 50-gallon tank doesn't provide enough for us. I could replace the water heater with a larger one but that seems unnecessary since the current water heater works well - when it fails though I'll probably get something larger. I also like that the mixing valve lets me keep the water in the tank at around 140F, which should prevent issues with legionella bacteria.
 

Jeff H Young

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ok well i guess that makes no differance how it was plumbed befor . Ive never used that valve Id have to contact manufacture or go online for thier instructions regarding check valves. but I wouldnt install as planned
 

Jeff H Young

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I think the purpose of the existing mixing valve was to store very hot water and then mixing in the cold that way if you need 5 gallons of 130 degree water you don't need a full 5 gallons from the tank because its going at a hotter temp . you wont run outta hot as quickly.
 

Jeff H Young

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See https://terrylove.com/forums/index....e-and-recirculation-system.81352/#post-588005 #6. That system uses a mixing valve made for the purpose.

Three check valves, although the pump may have one built in.

yes 3 check valves is not installed the same as jayess has drawn . I would try to look at an identical valve or manufacture instruction.
btw the valve you show reference to is a cash acme (not much help) just confuses things unless you suggest his is the same to hook up. which it may or may not be
 
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Jeff H Young

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Forget everything else and run with the manufacture diagram exactly , is my recommendation.
 

Fitter30

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Keep adding check valves will find water pressure is lower and return line might stop working. Pump won't be able to over come the head pressure. Like other wrote follow the manufacturer diagram.
 

JayEss

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That's what I thought, thanks! One more thing:

My house is plumbed with PEX and the dedicated return line has a 1/2" copper stub-out. What's the "right" way to hook up the pump to that stub-out? From my understanding I don't want to sweat the copper stub-out since the heat can damage the PEX in the wall, so I was thinking I could use a compression x FIP fitting and an MIP x PEX barb and then just run PEX for the whole thing. Or is there a better way to do this?
 

John Gayewski

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Kind of hard to say the best way to pipe the pump without seeing everything in context. Your plan sounds fine.
 
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