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old monoflo conversion

newagedawn Member Posts: 586
hello all, i have someone who has an old monoflo system from the fifties, and would like to convert the baseboard to cast iron radiators, can someone give me some info on how to do this? one area has 26ft of baseboard on one monoflo tee, how to convert? the main is 1 1/4 and tee's off to 2- 1" returns back to the 1 1/4 return to boiler the branch piping is 3/4 to the baseboard, some detailed tech support needed!!!! tx
"The bitter taste of a poor install lasts far longer than the JOY of the lowest price"


  • Big Ed_4
    Big Ed_4 Member Posts: 2,377
    edited January 2020
    I would recommend looking at panel radiators rather then equal out put baseboard .Baseboard its a different animal , Designed for price rather then comfort . Baseboard is designed as a series system and not a good retrofit for an mono radiator or convector system . The spacing of the tee's with the diverter on the return, with an up flow riser, minimum tee spacing distance the width of the radiation . See the problem with equal amount of baseboard..Also you need to add a bleeder at the highest point You need an upward uphill pitch to the bleeder . If can not add a purge valve set up on one of the risers ..

    With a down flow radiator add two mono flow tee's to over come the downward resistance .Extra tee spacing increases the pressure drop , Good to know when designing

    Next proper water flow is important . Large water flow makes the venturies work well (pressure drop,) Use a single circulator for this zone and don't add restriction.Use of zone valves and reduce piping are a negitive to this system.This is an ingenious system designed to distribute equal heat though out the building . Unlike baseboard . Alternating incorrectly or cutting on these basics will alter it's design .. All the $%&! installs show up on the coldest days of the year .
    I have enough experience to know , that I dont know it all
  • ch4man
    ch4man Member Posts: 294
    FWIW, i have never done installs or designs. but.....
    my 1st thought is to scrap the monoflow mains and homerun the
    rads with CI to just under the floor to preserve the old school look and finish with PEX back to a manifold in the boiler room.
    keep the PEX straight to avoid air traps
    EBEBRATT-Ed Member Posts: 13,834

    I see no reason to scrap the mono flow. Changing all the piping costs $$$ and will do nothing for comfort unless he wants more zoning.

    You changing from baseboard to cast iron correct?

    First thing is a heat loss of the space
    then locate the radiators and size the piping based on the flow rate you need.

    One you have the number and size of the radiators you can see if the existing mono flows will work or you can put a few new ones in if needed.

    The alternative is rip all the old stuff out and install new hot water manifolds with pex to the radiators.

    Depends on the $$ he wants to spend
  • mattmia2
    mattmia2 Member Posts: 8,437
    There is no reason you can't put TRVs on the radiators if you want that, right?
  • Big Ed_4
    Big Ed_4 Member Posts: 2,377
    Not on a mono flow unless you add another diverter at the radiator .. Shunting off an riser would effect the rest of the system ..Added note , Unused set of risers , either remove the Venturi or connect the unused risers ...Repete "No restrictions of flow " Back to panel radiators , you can buy the optinal bolt on diverters when you add the optional slide on TRV's ... I would also add an auto circulators if I was going that way

    I have enough experience to know , that I dont know it all
  • newagedawn
    newagedawn Member Posts: 586
    thanks all for ur comments but i found the answer in the b and g handbook its a gem for monoflo systems, its all the calculations i needed
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"