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Modifying Takagi Jr to handle radiant heat

DD_5
DD_5 Member Posts: 36
I'm looking at a Takagi Jr, NG unit that is now providing radiant heat for baseboard rads. The problem is it's efficiency, lack of it, because as long as there is a call for heat from either of the two t-stats the circ pump sends flow through the Takagi (and then through a two way zone valve) and as long as there is flow through the unit the burner is firing and the flue fan is on.

I'd like to add a high/low limit that switches the takagi  off but allows the pump to run as long as the t-stat calls for heat. This would include a 20 degree delta T, switching the Takagi back on once the temp in the primary loop drops to the lower temp. I'm thinking creating a cycle will lower the gas bills and electrical. Anybody have ideas of a good way to do this if this is the way to go? I'm thinking Honeywell aquastat...
Double D

Comments

  • CMadatMe
    CMadatMe Member Posts: 3,086
    Hate to Say

    But it is what it is. Your way out is a storage/buffer tank. Have the water heater supply the tank and draw from the tank for the radiant. You then could use a aquastat to turn on a pump when the tank needs to be satisfied. Funny thing is by the time you add up all the extra cost ontop of the orginal cost of the Takagi you probably could have purchased a mod/con boiler that is made to do the job. 
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • DD_5
    DD_5 Member Posts: 36
    Squeeze a nickel

    spend a dollar....Thanks. A buffer tank it is.
    Double D
  • DD_5
    DD_5 Member Posts: 36
    Flat plate heat exchanger instead of buffer tank

    Would the right pump control combined with a flat plate HE (or a Taco x block) work at all or do I have to have the thermal mass of a buffer tank? I could set the delta T between the system side and the heater side so that the heater pump cycles instead of running continuously...It looks like the X block handles this easily but again, do I just have to have that thermal mass? 
    Double D
  • joel_19
    joel_19 Member Posts: 931
    buffer

    Heat exchanger adds no mass will gain you virtually nothing. Buffer is the way to go if you really want a water heater doing a boilers job.
  • Gordy
    Gordy Member Posts: 9,537
    Funny

    Instantaneous water heater+Buffer tank= Tanked water heater, for cheaper



    Not that I care for either  to do a boilers job unless the load is real small.



    Gordy
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Funny

    Gordy you make a great comparision. Your absolutely correct. You just made a water heater. I just posted on another thread about how I dislike water heaters for radiant unless a very small load. Happy new year.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Gordy
    Gordy Member Posts: 9,537
    The point

     Being some people think they are saving big money with a tankless as a boiler. When in the end with the necessary modifications they end up being the same cost, and less efficient. Or a tanked water heater they could have spent way less money on.





     Happy new year !!          Gordy
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