Tankless heater and Kohler K-682-K DTV system

Discussion in 'Tankless Water Heater Forum' started by Nicholas_ii, Mar 5, 2009.

  1. Nicholas_ii

    Nicholas_ii New Member

    Perhaps this should be in the shower forum, but it's tankless related question.

    Now that I"m installing a tankless system, I see there is a "Supply Pressure Differential" spec of 5psi in the K-682-K manual (the 6-port thermostatic valve that works with the DTV system).

    Does this spec mean that the Hot water pressure can't be more than 5psi less than the cold water temp?

    If so, how could a tankless ever work with this system, given that water pressure drops with temp?

    It says that "pressure regulators" can be installed, though I don't know what those are or how they work.

    Any thoughts?

    This is the doc I'm reading http://www.us.kohler.com/onlinecatalog/pdf/1043183_2.pdf

    Last edited: Mar 5, 2009
  2. I think you are in trouble...

    I think you are in for a lot of fun...

    expecting to fine tune a tankelss water heater
    to a 6 port thermostatic valve made by Kohler,,,,
    (looks like something that you would see on the space shuttle)

    that looks extreemly complicated....

    you lost me on the second page of those instructions...

    and also keep in mind that anything from Kohler
    I would never trust or expect to work right in the first place..

    you are in for some real hair pulling fun......


    Last edited: Mar 6, 2009
  3. Nicholas_ii

    Nicholas_ii New Member

    The alternative is to use the Kohler K-669-KS Thermostatic valve I guess with a bunch of volume controls.

    We're doing kohler faucets and trims elsewhere in the bathroom. I don't think doing 2 different brands and trim is going to fly with the Mrs. She loves the water tiles.

    Are Kohler valves that bad?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Kohler is infected with the not invented here and I can do it better syndrom...they are constantly changing their both internal and external designs...their parts book is like a phone book. As a result, few places, even Kohler themselves, stock parts. If you search here, one customer was told by Kohler that, sorry, the people that made that are no longer in business, you'll have to install a whole new one when looking for a repair part.

    It has been reported, and I think it was Delta, that said outright that their stuff does not work well with a tankless system.

    For a tankless system to work, it almost always has a flow restriction in it that means, depending on volume needed, the outlet pressure from the hot side will be changing.

    It appears Kohler is saying that if you install a similar flow restriction (pressure regulator) on the cold side to match that on the hot, it would work. How well is another issue.

    Flowing lots of water through a tankless if you live in a cold climate may lead to really poor results. It is extremely important to understand and size the unit accordingly. Failure to do that will cause you to end up with an unsatisfactory experience.

    While I can understand the desire for multiple body sprays, from a practical viewpoint it is an extreme extravagence, and to get it all to work, ALL parts of the supply and systems involved must be sized and tuned to work. It is a HUGE energy hog...heating water in volume 'instantly' takes really significant power inputs.

    Good luck...
  5. Redwood

    Redwood Master Plumber

    Well stated Jim!
    So well stated in fact that I can't think of one thing I would add except this picture of a Kohler engineered device...
    Their version of a toothpaste dispenser.

  6. Nicholas_ii

    Nicholas_ii New Member

    Are there thermostatic valves that work better with tankless systems?

    For a 12GPM system, it is very clear on Kohler's site which valves can handle the water volume. I did a quick look at Moen's, Delta's, and Grohe's sites and find it very hard to find technical details of the valves themselves. Particularly with respect to flow rate at pressure.
    I've never really considered part availability, as I guess I expect the things to not break!

    Thanks for the input.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Most manufacturers use only a few different rough-in valves, and then have numerous choices of trim, so you have to decide whether to look for the trim you like, then see if it has a compatible rough-in valve, or look at the rough-in valves, then see what trim will fit it. In a big-box store, they tend to sell the stuff as kits, rough-in and trim. Most any good supply store sells them as piece parts.

    To get 12-gallons/min, you will need to start with 3/4" supply lines and a 3/4" valve. Trying to use 1/2" lines and valve will be dissapointing. Anything less and you will have problems either with pressure or volume. Also, depending on where you live and how the supply is routed, your winter incoming water could be anywhere from nearly freezing to 60-degrees or maybe even more. that incoming water temp will radically affect how much hot water you can get from any tankless. Then, consider the amount of mix you need to produce the desired temperature - in the winter, it could be nearly all hot, in the summer, it might be half of that. You'll need a water heater that can flow nearly that 12 gallons if your incoming cold is at the verge of freezing. It can be done with a tankless system, but it will not be cheap. You might find you need to restrict your use of the body sprays to the warmer months if you don't size things properly.

    My personal experience is very limited - I've used Grohe stuff on my remodel and on a couple of other projects. The rest of the knowledge is from reading and discussions, so your best bet is to wait on one of the pros with more practical experience.
  8. Nicholas_ii

    Nicholas_ii New Member

    I'm in Central Texas, so the temperatures are rarely that cold.
  9. the biggest problem

    Basically what you want are the body sprayers so that you
    and your wife can jump in the shower together......

    Depending on what you had in mind I would suggest
    a 75 gallon gas water heater or perhaps 2 in series
    cause you dont want to run out of how water at the
    wrong time....

    the pressure balanced valves could also spoil the moment
    with erratic cold and hot water cooling criticle things down
    when you are trying to heat them it up.....

    you get the general idea of what I am talking about...

    I hate it when that happens........
    Last edited: Mar 6, 2009
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