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Thread: tankless recirculation

  1. #16
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default It's not as simple as just adding a recirculation system!

    So, basically, with a tankless, you need another WH, albeit small, to supply the recirculation loop. that makes sense, as keeping the tankless on the whole time the recirculator is running would add signficantly to the typical duty cycle. So, you can't or at least shouldn't JUST add a recirculator - there's more to the story.

    Thanks, you've confirmed my thoughts.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  2. #17
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by gmt View Post
    I've installed recirc systems with tankless. You definately do not want to utilize the tankless as part of the recirc system or, you cut the 10 year warranty in half. But if you use a little Ariston, (say eight gallon) with a pump and expansion tank you will have little problem. The small electric w/h supplies the recirc, then once the call for hot water is triggered the Rinnai flows through the Ariston, ensuring it is kept hot.
    I have one where the Rinnai is approx. 100' or so from the master bath. The cust has never complained about waiting for hot water. This was installed about 2 years ago
    If you put the 8 gallon Ariston AT THE MASTER BATH then you don't need the recirculation system. The small amount of water in the supply pipe mixes with the 8 gallons in the Point-of-Use heater to keep the temperature up where it is delivered and the tankless heater will supply the makeup.

    Avoiding the recirculation will avoid the constant loss of heat due to recirculation of hot water from the heater. Because the objective is to keep the water in the supply pipe hot there will be heat loss from two pipes that must be made up by electric heating.

    The recirculation pump and pipe are unnecessary.

    Keep it simple. Skip the recirculation!

  3. #18
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    If there were multiple bathrooms you wanted to keep near instant hot water to, you'd still want the recirc, but I think the complexity and energy costs may make it kind of expensive. Then, I suppose if you've got a house big enough to need it for multiple bathrooms you may be able to afford it, too (at least for now!).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #19

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    Tons of good discussion here.

    So the option of an on demand type recirc system (Taco or Ready Temp) that push the hot back up the cold line is not a good option for the Rinnai system. I did not like the idea of having luke warm water in the cold line anyway. Certainly do not want to lesson my warrantee.

    Using a point of use tank with out a recirc, I do not think will work for me as the tankless is located 35 feet from the master bath, and 60 feet from the Kitchen. I would most likely need two instant hot tanks (still may be more economical though).

    It sounds like my best option would be to install a small electric tank in accordance with the Rinnai schematic shown in their installation manual. In my case I all ready have the old existing recirculation line. I will just need to extend it 30 feet.

    If I go that route, what size electric tank do I install (Rinnai recommends 2 -5 gallons)?
    What size recirculation pump? (I plan on using the UP10 series from Grundfos). This is a small pump with temp sensing controls; I hope it is enough hp.
    In addition, what size expansion tank should I use? I have know idea why an expansion tank is recommended from Rinnai

    Thanks again to everyone for all of the good discussion.

  5. #20
    DIY Junior Member gmt's Avatar
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    On the size of the water heater you need to make sure that it has 3/4 inch inlet AND outlet, because the main hot line sytem also runs through this. I have found the Ariston 8 gallon model to fit the bill.

    A normal Grundfos recirc pump to be sufficient. The timer model is nice in that it doesn't have to run at times when there is no need.

    The expansion tank is around 2 gallons and just a normal water heater safety tank. It's main purpose is for the "closed" system of the recirc line.

  6. #21
    DIY Junior Member gmt's Avatar
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    Default

    Name:  STUFF 004.jpg
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Size:  26.5 KB Here is one installation. It is installed as per Rinnai specs.

  7. #22

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    GMT, thanks. The picture helps a bunch. Please see the attached. I want to make sure I completely understand the plumbing. I have labeled the pipes. Let me know if my assumptions are correct.
    Attached Images Attached Images  

  8. #23
    DIY Junior Member gmt's Avatar
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    Boy that picture is big!

    That's pretty much it. Just go by the diagram (Noritz/ Rinnai) whatever and install the check valve where it says.

    My advise is to stick to one of the big three manufacturers...Rinnai, Noritz or Takagi. I believe all three have somewhat similar systems

    Good luck!

  9. #24
    DIY Senior Member rdtompki's Avatar
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    If you go to the Noritz website you can pull down a pdf installation manual for one of their WH, the 69M for example. They have a diagram of an approved recirc system. I put in the tankless at the far end of the house as part of a remodel. Didnt choose to recirculate, but I have considered a Chilipepper recirc. pump or similar. Could use an X-10 outlet to control from some other point in the house. For the time being I just run the water as long as necessary; only the kitchen and laundry room are affected so this is not too critical.

    If the hot water demand is large you might consider two mid-sized units like the 69M. These can be mounted in parallel and will self-control via a cable interface. I've been very happy with the unit so far (1 year). Love the constant temperature water.

    Rick

  10. #25

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    I just purchased a new construction home in Austin, Texas with a Rinnai tankless system. It has two Rinnai units mounted in the garage. There is no recirculation line. The home is 3500 square feet.

    The problem is that the master bath is connected to the Rinnais with about 70' of 3/4" copper. It takes over 4 minutes to get hot water. Is there anything that can be done? I'll be meeting with the builder next week.
    Last edited by drewcwsj; 02-10-2008 at 09:06 AM.

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