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Monoflo system

gpjazz
gpjazz Member Posts: 28
in Radiant Heating

Hello all.. Got a question about adding new, additional baseboard (fintube) radiator to an existing monoflo system. Customer is building a new room addition on the house so needs an additional radiator.

My issue is that I don't have a lot of linear piping to work with on the main loop in the basement to add 2 more monoflo tee's and have them spaced far enough apart from each other. If I did this and kept all the existing tee's as they are, I only have about 4 feet of linear piping on the main loop to work with. I understand how water flows thru a monoflo system, flowing thru path of least resistance. And that is another issue. Because the new room addition and new radiator will have a long run of 3/4" piping… Longer than I want. But there isn't much other choice. It will be about 14 feet of 3/4 piping out to a 10 foot radiator, and then 14 feet back to the main..

So my question is, what is the best way to do this?

Would it be an option to instead connect the new radiator to an existing radiator in the adjacent room using the existing monoflo tee's? This would obviously make the total length of piping/rads longer and create more resistance to flow.

Or would it be better to just add 2 additional monoflo tee's for the new radiator? But like I said, I only have about 4 feet of piping to work with on the main basement loop.

Could another option be to install a valve on the 1 1/4 main loop between the tee's and adjust valve to control flow?

Any thoughts will be greatly appreciated. Thank you

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 25,968

    Monoflo systems are… twitchy. If it were mine to play with, I'd take your last opeiong — basically pipe your new radiator by T ingoff the existing pipe cand running out to and back from the new radiator, and putting a valve on the existing pipe between the takeoff for the new radiator and the return. Now as a bit of extra flair, you could make that valve a zone valve and set it up with a thermostat in the new space, but "reverese acting" — that is, when the new space needed heat, you'd have the valve close. You could do that with a relay very neatly to reverse the action of the thermostat.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mattmia2
  • Mad Dog_2
    Mad Dog_2 Member Posts: 8,074

    Why wouldn't you add a seperate zone for this new addition? Leave the monoflo zone alone. Mad Dog

    Consulting by Mad Dog & Matt Jr.
    LRCCBJSTEAM DOCTORmattmia2EdTheHeaterMan
  • Mad Dog_2
    Mad Dog_2 Member Posts: 8,074

    Better to be able to have independent control of the addition's heat. Mad Dog

    Consulting by Mad Dog & Matt Jr.
    LRCCBJSTEAM DOCTOREdTheHeaterMan
  • LRCCBJ
    LRCCBJ Member Posts: 1,027

    You didn't specify if the main is 3/4 or larger. If it is 3/4, you certainly should NOT add any additional monoflo tees otherwise you'll be installing a larger pump. 3/4 is marginal on any monoflo system.

    Follow the advice of Mad Dog and install a new zone for the new room. Leave well enough alone with the existing monoflo.

    mattmia2EdTheHeaterMan
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,362

    Agree 100% with the big dog. Separate zone or bust. I would never do what you are suggesting. Because plain and simply, any problem from now until eternity, you are married to.

    mattmia2EdTheHeaterMan
  • mattmia2
    mattmia2 Member Posts: 12,575
    edited April 10

    separate zone. you're going to spend more time and money trying to get it to work off the monoflo loop than it would cost to run a separate zone back to the boiler and you still won't get it working well. the addition will heat differently than the main house too.

    Mad Dog_2
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,682

    Agree with the posts above.

    Don't touch the Monoflow zone. Add a second circulator and make the new room its own zone.

    Don't add a zone valve to the Monoflow you will restrict it.

    Do the zoning with circulators and add flow check valves if needed.

    mattmia2Mad Dog_2
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,391

    If you take the time to research how to properly design a Monoflo® tee system by selecting the proper size diverter tee from this Monoflow Design Guide in order to determine the actual pipe sizing needed and if you require one or two diverter tees on that particular radiator and how that will affect the remainder of the radiators on the system, you will ultimately make the determination that a separate zone is more efficient and a better use of your time in properly designing an alteration to the existing "working" design that is already there. 

    Screenshot 2025-04-10 at 1.58.52 PM.png

    Or you could guess and hope for the best!

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    delcrossvEBEBRATT-Ed
  • gpjazz
    gpjazz Member Posts: 28
    https://forum.heatinghelp.com/discussion/comment/1851850#Comment_1851850

    The main loop is 1 1/4"

  • gpjazz
    gpjazz Member Posts: 28

    I didn't want to make the system zoned… It is currently a single zone system. So to make it zoned I'd have to also change some of the main piping at the boiler as well..

    And also the new room addition is on the far side of home from where the boiler is. Zoning is just a lot of extra piping work and controls/pump/ect. that the customer simply can't afford

  • delcrossv
    delcrossv Member Posts: 2,142

    How many emitters presently?

    What size takeoffs for those emitters ?

    What pump is presently installed?

    You'll have to do the math to see if you can sneak in an additional emitter.

    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
  • gpjazz
    gpjazz Member Posts: 28

    There are currently 7 radiators total. ( new room will make 8 )

    They are all 3/4" directly off of the 1 1/4" main.

    I'm not certain what pump is currently installed, but I'm pretty sure it's a Taco ecm variable speed circulator.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,682

    You can try adding another rad. If the branches are long you may want a Monoflow tee on the supply and return. May or may not work. The extra resistance of the Monoflow tees may cause a problem

    There is another way that will not screw up the Monoflow system. Cut in two standard tees into the Mnoflow main 1 1/4 X 3/4" and feed the radiator off that. In one of the pipes supply or return install a small circulator to feed the new radiator. Control both circulators of the same thermostat. Put a balancing valve on the radiator feed to control flow.

    By using two standard tees the Monoflow system will work as before. Regular tees will not restrict the Monoflow loop like Monoflow tees will

    bburd
  • LRCCBJ
    LRCCBJ Member Posts: 1,027
    https://forum.heatinghelp.com/discussion/comment/1851890#Comment_1851890

    Excellent.

    I'm sure you can add another radiator to a 1 1/4 system without compromising the flow rate to any significant degree.

    Just to be sure………………

    Get the system running for at least 30 minutes. Measure the supply temp and the return temp with an infrared gun (put some black tape on the copper). Provided the DT is not excessive (greater than 20F or so), you'll be fine with the additional rad.

    FWIW, I have struggled with a monoflo with 3/4" piping and I could not get the DT below 25 even with a Taco 11 pump. The six monoflo tees coupled with the 3/4" piping was an exercise in futility.

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