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3-way mixer under tankless??

TimcoTimco Member Posts: 2,802
I'm finally doing some near boiler piping and connecting new copper from the house to my Quiet Side 120k. It's fun trying to make 4 tappings that are 2-3" apart look nice!!

So the tappings for tankless are 1/2". I want to do what I can to increase performance, so I'm planning on using a 3-way mixer. Any thoughts on this?

I love the easy math questions!! 0-0=0!
Working on steam and hot-water systems isn't rocket's actually much harder.


  • hot rodhot rod Member Posts: 6,485
    check the mix valve

    that you are considering, not all are approved for use with tankless heaters.

    I'm not sure adding a mixer will increase performance, if the heater doesn't store any water? Set it for the max. temperature you need and let it modulate to the load. A 120 should give you 3 about gpm even with cold wintertime water temperatures, in your area.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • TimcoTimco Member Posts: 2,802

    My rep at Hajoca recommended a mixer, but I posted this because I've never used one on a tankless, just a tank.

    We have a 2-bath house, and the shower we use has a nice higher-flow head, but we will never run 2 showers together or any two fixtures really. Sounds like I don't need the additional part, which is good.

    The valve is a Taco that was on their close out table but has a tankless diagram on the box showing that valve on a tankless.

    Thanks, Tim
    Working on steam and hot-water systems isn't rocket's actually much harder.
  • TomTom Member Posts: 446

    Here in Vt we are required to put a mixing valve on ALL potable water heating devices, it is ridiculous. I have had the best success with the caleffi it is machined very well meaning no more little weeps or leaks after a week or two in service, and you can almost finger tighten it to the point of no leaks. It comes with a built in well thermometer and for us in Vt it needs to be lead free and they are. They havent been an issue on any combo or on demands as of yet.
    Montpelier Vt
  • hot rodhot rod Member Posts: 6,485
    thermostatic and tankless heaters

    the challange is that some low mass, high fire type tankless heaters can have pockets of extreme temperature water when they first flow.

    A thermostatic valve needs a few seconds for the wax cartridge to sense and react to the sudden, and large temperature increase.

    More and more tankless manufacturers are adding some mass, usually a small buffer tank, or capacity in the coils to address this, and the "cold sandwich" potential.

    So, it depends on the type and style of heater you are installing. The Caleffi 521 has been tested with many, of the tankless heaters.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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