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Tying in radiant loop with baseboard

4cefed370 Member Posts: 7
edited February 2020 in Radiant Heating
Hi all, Ive been reading here for some time and have done some radiant jobs in my old house in the past pulling from the boiler outlet through 3way mixing valve and returning from the radiant loop to the boiler return with baseboard loops.

Im now helping a friend out and adding radiant loop in in his kitchen renovation. System has 3 loops, 2x 250ft loops for the kitchen/mudroom and a 3rd loop @75ft for a small bathroom and leaving 2 extra loops capped for future reno of 2 bathrooms. With the heatloss calc I have about 12kbtu on design day for the kitchen/mudroom and the bathroom is an interior room above and below conditioned space so its more to have a warm floor in there.
I came up with a calculation that a 12deg DT @1gpm will get me 12kbtu between the two 250ft loops. I am gonna use a grundfos alpha 2 pump since the future bathrooms will have zone valves and it can run on dP.
So its an old boiler that will most likely be replaced in next couple of years and it has a single circulator on the return with 3 zone valves and I dont want to start repiping everything if I can work around it. I wanted to basically add a new zone from boiler but basically it will be a short loop between the supply and return headers and utilize the close spaced tees method from it. I will add a balance valve to keep the water from short circuiting through this loop and starving the basboard zones if they call. This continuous flow loop will also return boiler water along with the low temp radiant loop water to protect against damage to boiler also, which may not be necessary because its a small load on the 130kbtu output boiler but it should be safer.
I drew up how to pipe it and dont see why it wouldnt work but I havnt really seen anyone do it like this so I wanted some opinions or constructive criticism please

Thankyou very much


  • Snowmelt
    Snowmelt Member Posts: 1,383
    I wouldn’t, I would like to see three pumps, one just for the p/s piping, after that the air Seperator , ex pump then pump for the two zone valves then another pump with mixing valve for radiant
  • 4cefed370
    4cefed370 Member Posts: 7
    Ok so your saying leave the current pump on boiler return which will be a primary loop circ, then add a pump on the boiler outlet but position it after the loop to the radiant so that its only feeding the 1st and 2nd floor zones. This will turn my system into a primary secondary system.
    It currently is not primary secondary as you can see but I guess Im kinda trying to make it a hybrid in a way? But you dont think it will be ideal. Now the only thing is the basement loop, does that need to be tied in after the new circ feeding the 1st and 2nd floor or can it be fed by the primary loop circ the way it is?

  • 4cefed370
    4cefed370 Member Posts: 7
    I guess it wouldn't be too difficult to convert it to primary secondary like this if my original plan isn't going to work properly

  • SuperTech
    SuperTech Member Posts: 1,854
    You could also try to pipe it for variable speed injection using a delta T pump. You wouldn't need the mixing valve.
  • hot_rod
    hot_rod Member Posts: 18,160
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • 4cefed370
    4cefed370 Member Posts: 7
    Ok thankyou hotrod thats exactly what I was looking for, ive seen some articles from John S. but not that one. So in figure 2 the "wild" circuit is exactly what I originally had in mind and it's the easiest approach for this job.