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Preferred domestic recirc piping

Hilly Member Posts: 421
So I'm just curious how you guys like to pipe your domestic recirc lines. ie. two checks and and fee on the cold inlet, or circ in bottom drain port, etc. is there one setup that is "engineered approved"? Do you always use expansion tanks? I'm really just interested in any "experienced" practices you guys are using.


  • pipeking
    pipeking Member Posts: 252

     there r many differant way to pipe a recirc. u need to follow the recomendations of the heat engine,mixing valve.pumps,ect.... when a mixing valve is used ,and surtain gpms need to be meet,ubtained,or exceeded, it needs to b noted.
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited February 2013
    All different...

    I do them different all the time ,depending on the system, new, retro, ect....

    Last year I did a retro, a friend of mine built an addition and now had a bathroom about an additional 50 feet away from any other appliance.... He originally wanted me to install a Rinnai tankless just to supply that bathroom with hot water, I talked them out of it, the gas line would have been 120ft through a finished property, no thanks...

    I ended up fishing 1- 3/8" pex line up to that bathroom from the tank, I teed it into the hot line under his vanity, with a check valve, aquastat, and 009 circualtor. I wired the aquastat into the bathroom light switch, then onto the circulator...

    So now they turn the light on, if the aquastat isn't satisfied, it will pull in the 009 and circulate the water from the old hot water line back to the tank, until it is satisfied, he gave up a little real estate in his lower vanity, and running that pex took almost 3 hours, but it works with no problems or complaints yet, and believe me his wife would be complaining if it didnt work..

    But all of them differ, on a new construction system most of the time I put a tee on the furthest hot takeoff and return it back to the tank... if it goes in 2 directions I will run 2 loops...

    I had a loop in my house but hated hearing the rinnai start when no one was using the hot water, so I installed an electric tankless before the 2 upstairs bathrooms, it works takes about 3 seconds to get hot water vs 12, and the electric tankless only runs for 10 seconds before the rinnai unit takes over, plus we have electric backup, and I haven't noticed a change in the electric bill at all, the electric tankless running for 10 seconds probably costs the same as running the well pump for the extra time.... Plus Im not wearing out tankless heat exchangers just to recirc...

    So there are a few ways to do it, kind of a case by case though, if the plumbing tees too soon and goes in too many different directions {I have seen this a lot with the new craftsman style homes} you have to do some thinking to make sure it doesn't cost too much in materials and time...
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited February 2013

  • hot_rod
    hot_rod Member Posts: 19,260
    edited February 2013
    The best method

    that I learned many years ago from a 2004 PM mag article by Julius Ballanco. Julius is an engineer that works a lot of scald lawsuits and sees many improperly piped recirc/ mix valve installations. A ASSE 1017 valve is NOT and anti scal device.

    If not piped with the two path to the valve cold and the tank, you will experience temperature creep when the system is un-used for a period of time. What happens is the warm recirc goes into the cold port of the valve. the valve responds to hot at the cold and allows the valve to modulate. So eventually the entire loop will be at the tank temperature, until someone opens a faucet, flushes that hot slug out and the cold port of the valve now sees cold and can modulate and mix the outlet to the correct temperature.

    Symonds has the same piping suggestions.

    Coffee with Caleffi had Julius as a guest presenter on DHW/ recirc piping, that 1 hour webinar is archived at the site if you want to see drawings and hear the explanation. And some great stories from Julius's experiences.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    I'm testing a simpler alternative

    and so far it's working quite well.  If you can dial down the recirc to the point where it just overcomes the heat loss of the loop, you eliminate a lot of the complexity.  The variable speed versions of Laing/B&G ecoricrc e-series pumps turn this into a trivial exercise, and really minimize pumping costs.  We also put a thermistor on the mixed DHW output and alarm if it goes out of range.  This also eliminates the need for heat traps on the valve inlets.  I like to know when something needs fixing.
  • hot_rod
    hot_rod Member Posts: 19,260

    show me a drawing. if you are only pumping the tempered line eventually the recirculated water will cool from heatloss of the piping. You would still need to push a portion of the water into the tank to supply tank temperature water to the hot port of the mixer?

    I like the variable speed idea, but I think you still need to run the recirc return into the mixer cold, and the tank, maybe you eliminate the "injection" balance valve, but same amount of checks and connections.

    Recirc could be done with electronic controls or mix valves also, but most AHJ still want to see an ASSE listed device in the system.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icesailor
    icesailor Member Posts: 7,265
    Overheating Recirc:

    I had this problem in a nursing home that had two water heater temperatures. It did exactly what you describe, heat up the loop during the night when there was no flow. I installed a Leonard TM-80 valve which returns through the valve and the system. It was originally designed and installed with a Watts 2" N-2 hot water extender valve. Not a thermostatic mixer. I thought of the system as a radiant floor panel and installed a Danfoss thermostatic valve on the return so that as the return water heated up, it sent all the water through the TM-80 and as it cooled down, some could pass back through the tanks. Because the TM-80 requires a very high flow, I replaced the Taco 110 Bronze with a high flow Bronze Taco. I don't remember which one. Just that it is a cartridge type with fins and it pumps a lot of water.

    The whole system as originally installed was a disaster. My band-aid has been working for over 20 years.
  • Kendo
    Kendo Member Posts: 3
    Recirc line on a tankless Coil

    Has anyone done a recirc hw line on a tank-less coil?  If so whats the best way of piping it?  The tank-less coil has a tempering valve installed on it right now. Thanks
  • Zman
    Zman Member Posts: 7,446

    Hot rods drawing is must. If the returning water must have access to the cold side of the tank and the valve.

    Swei makes a great point. Too many systems are over pumped. This leads to pipe wear and waste.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Hilly
    Hilly Member Posts: 421
    3rd tapping

    Why is it that not many of the diagrams use the 3rd drain tapping on the water tank for the recirc line? ie. Remove drain, add tee, add drain and recirc line.

    Is this a less practical way from an engineering standpoint? And how would you consider installing a recirc that doesn't involve a tempering valve?
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