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80 % boiler with low temperature application

Snowmelt Member Posts: 1,399
keep it simple, I don't want to sell a new boiler if they have a 5 year old boiler. but they are thinking of making three rooms radiant. with a standard atmospheric boiler ( going through the chimney) I want to add three zones and make 2 more so it will be a total of 5 zones. How would you do your near boiler piping and keep the flue gas high enough to avoid condensation. I would like to also add a hydronic separator to the job ( actually would love to make one myself. Boiler is a weil mclain 120,000 btu in 100,000 btu out the existing baseboard heat is warm enough to heat the house. any more info needed?


  • Jamie Hall
    Jamie Hall Member Posts: 22,100
    Mixing/tempering valve for the feed for the radiant loops -- allow just enough high temperature water in and out to meet the load and let the rest just recirculate.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Rich_49
    Rich_49 Member Posts: 2,762
    4 Way I Series w/ ODR George and a circ for the radiant .

    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    Paul PolletsGordykcoppTinman
  • Dave H_2
    Dave H_2 Member Posts: 534
    edited February 2018
    I would add the Hydro-Sep, great for maintaining that high temp return to the system and then add mixing for the radiant on the load side of the sep.
    If there is an indirect, pull that off before the hydrosep and then on the load of the hydrosep, first to come off is the baseboard zones and then the radiant. As Rich said, use a mix valve with outdoor reset, it will make a world of difference

    Dave H
    Dave H
  • archibald tuttle
    archibald tuttle Member Posts: 1,043
    think all the above are workable although especially on a cast iron boiler, which i assume this is, i often use an indirect tank as a radiant flywheel and complete separator. i started this way because many of the jobs i did were from the days before diffusion barrier tubing -- for that matter from the days before PEX itself, can you say polybeautiful. So I had to have separation. Even with diffusion barrier tubing, i believe it reduces but doesn't eliminate the effect -- kind of in the way the 'stainless' steel is not an absolute description, so too diffusion barrier tubing doesn't give you 0 diffusion. So if i have a copper or stainless heat exchanger boiler and all diffusion barrier tubing I don't sweat it. I hate aluminum exchangers so unless somebody gave me one i wouldn't be using it anyway. But iron is way out there galvanically so i separate regardless of tubing mix. You can use a plate style heat exchanger too which is cheaper but i found I liked the flywheel and that it kept the cycle length up without tempering the boiler side water. my 2 cents.
  • Snowmelt
    Snowmelt Member Posts: 1,399
    Thanks richie and dave I will hopefully get the job but I just wanted some ideas and I think it will work .
  • hot_rod
    hot_rod Member Posts: 20,725
    So a standard cast iron boiler? Some baseboard, some low temperature radiant?

    If it is a standard low pressure drop boiler really no value or need for a LLH.

    You do want to have return temperature protection however, and the only way to assure that is have a means to sense and respond to cold return.

    Here is another option, this uses a ∆P ECM circ, so high efficiency on the distribution. The radiant is via ODR and has a boiler return sensor to assure the boiler stay out of condensing mode.

    This gives you the best of todays technology, a circ that responds adjusts to changing loads, low temperature mixing, ODR, and return protection.

    It could be any type of mixing device on the low temperature but a control with return protection function would be my choice.

    Page 92


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,537
    I remember when ci boiler had bypass piping, and a mixing valve for radiant. K.I.S.S. It seems as technology comes forth one feels the need to use it. Ya know like the nest :D
  • BobC
    BobC Member Posts: 5,428
    @Gordy I learned KISS in the army and aside from FUBAR it was the most important thing I've learned in my life. Simple systems tend to work, not always the most efficient but if they stop they can usually be fixed with common parts.

    God Bless steam and cast iron!

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge