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Tankless for Radiant Layout

Sava Member Posts: 4
I need help in a diagram for two zone radiant. I have a Takagi T-K3 tankless water heater, a taco 011 pump, manifolds, expansion tank, mixing valves, Honeywell zone valves and the pex pipe is already layed out. Can someone help me design the layout from the start of the hot water to the end the cold return? I know I need to purchase more stuff, like the ball valves, check valve, air purger, and anything else that I may need. I would also like to add a zone or two in the future for the basement.




  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    step one

    is return the tankless heater, and the 011.

    Then, get a heat load done to figure out if you are best served with a mod/con boiler, or a tank water heater.

    Then, you can have a system that will serve your needs ideally.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Sava
    Sava Member Posts: 4

    It's for a small section 1000 sq ft and maybe 500 sq ft basement in the future.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    still depends

    on your heat load, but you're probably closer to a tank heater than a mod/con boiler.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Sava
    Sava Member Posts: 4
    See below

    Rob, I have a heat load calculations. I need help with the layout.

    Total floor area: 1012 ft²

    Radiantly heated area: 1012 ft²

    Total panel area: 1012 ft²

    Total tubing area: 1000 ft²

    Total room load: 17186 Btuh

    Total panel output: 17186 Btuh

    Total supplemental heat: 0 Btuh

    Total back loss: 2148 Btuh

    Boiler output required: 19334 Btuh

    Design temperature: 6 °F

    Maximum supply temperature: 142 °F

    Total flow rate: 2.25 gpm

    Maximum head loss: 5.05 ft H2O

    Total tubing required: 1418 ft

    Number of loops: 6

    Number of zones: 2

    Number of manifolds: 2
  • Unknown
    edited August 2009
    In my opinion,,,,

    systems are next to impossible to design on the internet.Why not meet face-to-face with a reputable designer/heating contractor in your area and pay him for this service? NOTE- Nothing bad against NRT Rob at-all intended! 
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    no offense taken

    though remote design is definitely possible, all things equal I can't beat a competant designer on the ground. I also can't design a system in a forum post.

    That said, with a 17kBTU load, unless the original poster is in a very, very cold climate, he's probably best off with a tank heater, and his k3 was just unnecessarily expensive for the relatively non-existent benefit he's going to get from the tankless. so rather than laying out the components he's got, he should send some back and get something more appropriate to his system.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Sava
    Sava Member Posts: 4
    New Jersey

    I already have the TK3 tankless, so if possible I would like to stick with it. I see that your not a big fan of tankless with radiant. I'm located in NJ. I guess what I'm looking for is a diagram or picture of a piping layout with the Takagi, so I know where I can put things. I'm not sure what other information is needed, but I'll do my best to provide it. Thanks for your replies.
  • EricAune
    EricAune Member Posts: 432
    edited September 2009
    Not made for radiant application...

    I don't think you will find a radiant piping diagram for this unit because it is not intended for space heating.  You will see a diagram for space heating and domestic, using a flat plate exchanger on their site.

    The TK3 is only about 80% efficient. So much of the efficiency is lost due to the flow control/delta T operation.  Your job is too small for a Mod/Con, however, maybe an electric boiler would fit nicely.  With an electric you can get outdoor reset and the proper flow through the system.

     I have changed out three units, all takagi, (installed by others) in the past two years by request of the owners due to higher than expected fuel consumption.  The initial presumption is "because its a tankless, it must save money....right?"

    In one instance this summer I had a customer change from LP (takagi unit) to an electric boiler.  I replaced the unit, took it back to the shop, and opened up the heat exchanger.  It was very dirty with restricted flow, I'm not surprised at its low performance.

    The piping layout for a tankless unit will be similar to an electric boiler.  Return directly to the cold side of the heater, out of hot into the air separator/expansion then pump away.
    "If you don't like change, your going to like irrelevance even less"
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479

    When I am installing a small radiant floor in a customers house I use a flat plate HX and extract heat from the existing water heater tank. An easy way to go is use the Taco X-block which has everything built in and ready to pipe. 
  • Leo_G
    Leo_G Member Posts: 89
    Still totally against

    these type of systems! They are very dangerous! If I remeber right, a few years ago, 2 families in Ontario lost their lives because of these set-ups. As Eric saw in his post above, the heat exchangers became blocked, and flooded the houses with CO.

    These heaters are meant to have a large Delta T, anywhere from 60 - 90*. At a Bosch training seminar just a few months ago, the instructor stated that their heaters are not to be used for space heating.

    Use an electric boiler, or run electric infloor - PLEASE!

    Leo G
This discussion has been closed.