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Monoflow System to Radiant Floor Conversion

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Peter_26
Peter_26 Member Posts: 129
Hello All,

Can the primary loop of a single pipe monoflow system be kept as is and the individual piping that provides heat to the individual rooms be converted to underfloor radiant plates? (Uponor Joist Trak) By this I am asking can the existing supply and return off of the main loop for each baseboard fin for each room be used to connect each under floor radiant loop?

I have thoughts of either keeping the existing boiler with a lower supply temp and using thermostatic mixing valves at each room circuit. I was thinking of eliminating the baseboard, tapping into the return and supply with oxygen barrier pex and the Joist Trak. Would this work or am I opening up to a slew of problems?

My other thought is of changing out the existing cast iron boiler, which is working perfectly ( Not my first option because why fix something that's not broken and has proven to be reliable) with a high efficiency model with ODR and still install the trak panels for the underfloor system.

Unbelievably my home seems to be undersized in the baseboard department for the year the home was built in (1965). I like the idea of using less fuel with less SWT, but if the baseboards are undersized, neither boiler, cast iron or high efficiency would be used to it's rated efficiency, unless I install more baseboard. Thia is why I was thinking of using the trak panels.

Any advice and observations would be greatly appreciated. I know there are a ton of things I am not thinking about because this is not my trade and you guys are by far the best forum I have been in that point out all the scenarios that I can go about accomplishing my objective. If pictures of my existing system are needed then I will post them.

Thanks,
Pete

Comments

  • Ironman
    Ironman Member Posts: 7,379
    edited December 2019
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    No, you definitely don't wanna use a monoflo system to supply a radiant floor. It will never work because the resistance in the floor piping would be way too high to induce any flow.

    Your first step is to do a room X room heat loss calculation to determine how many btus each room needs. A radiant floor may not be sufficient to heat some, or all of your rooms.

    It's not unusual to see a house your age need 25 - 30 btus per square foot depending on locale and construction. A radiant plate system is usually good for about 20 btus per square foot without cranking up the SWT above what's good for the wood.

    Start with the load calc. It's the foundation for all designing.

    SlantFin has a free app you can download to do it.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Peter_26
    Peter_26 Member Posts: 129
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    This is exactly why I posted the question here. Of course, something I did not think of was the head loss. Thanks for the reminder of the load calc too. I used the Slantfin Hydronic Explorer app a couple of years ago when I moved in and have the file saved.

    Just for one the bedrooms (5065 btu as per the app) alone I can see that the btus/sq ft is at 36 for the loss. I would need baseboard anyways to make up for the rest. I wanted to be able to do away with baseboard completely, but after you pointing out the downside of my idea I am not going to able to do that with the underfloor option. The home has all hardwood flooring too so from what I have read the SWT is limited to about 72F There goes that idea.

    I could see the option of adding more radiation but under the windows in the form of steel panel ones. Ultimately I would have to add higher output ones if I plan to go with a lower SWT with the same boiler or a condensing one. They are more on the expensive side, but the expense is needed one way or another with whatever decision I make. I just want to make the funds count the first time around.

    I am guessing that I would need to use the Slantfin App and change the SWT to 130-140 range to get the radiation needed for each room?

  • Ironman
    Ironman Member Posts: 7,379
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    A 120* SWT about the limit for most wood floors, particularly older ones that don't have modern sub flooring.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Peter_26
    Peter_26 Member Posts: 129
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    Thanks Ironman. I would rather go with the radiant panels, easier to install and I can keep the original monoflo. The radiant would be a costly investment too.

    I can keep the cast iron boiler for now and plan for a condensing boiler when I choose the radiators. Are there any panel radiators that you guys would recommend based on installation experience and performance?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,094
    edited December 2019
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    You need to add circulators to the branch circuit of each monoflo tee you pirate for other radiation design. I remember a @DanHolohan class I attended several years decades ago where he described how Gil C. (a B&G tech. trainer and all-around Hydronics Guru) invented Primary Secondary piping design in the 1940s or 50s because of a failed monoflo design. Gil C. added circulators after the branch tee to get heated water to the non-heating zone(s) or radiator(s). File this under "I Forgot more about heating than kids these days will ever know"
    I can't remember the specifics but I remember the concept.

    Edward Young Retired

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

  • Peter_26
    Peter_26 Member Posts: 129
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    OK EdTheHeaterMan. I've looked into the pressure drop of the Buderus Panel Radiators, but can't seem to find any info, but from your reply I am assuming that the drop is fairly significant if I would need a circulator for each circuit in my system.

    I've looked for specific values on the pressure drops for the Buderus Panel Radiators on SupplyHouse, but can't find anything.
  • Ironman
    Ironman Member Posts: 7,379
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    Panel rad's don't require a high flow rate. Most operate fine at .75 gpm or less, depending upon size. You don't need a separate circulator for each one. Much to the contrary, you can power several from one circulator.


    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 22,258
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    typically 3 in series, depending on their size. It's mainly that the end one runs out of SWT that limits the output, not so much the pressure drop as Bob mentioned.

    In series they install with adjustable H valves so you can balance them out a bit.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Peter_26
    Peter_26 Member Posts: 129
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    The panel radiators will be oversized for the rooms, but that's because I want to plan on a future upgrade to a 95+ boiler and lower SWT. I know the cast iron boiler that I have now is 30 yrs old and can possibly outlive me if taken care of, but we are working on flooring and I want to get the piping done before the flooring is completely in. In the meantime I can use lower SWT with a mixing valve with ODR .

    My boiler is not setup as primary/secondary and the monoflo system has worked flawlessly. There is a Caleffi ThermoMix TMV installed in the bypass loop on the boiler with a single circulator in the system. It's a split loop system, 1 1/4" to two 1" loops.

    So, since the panel radiators require less flow I should have no problem with using the same risers and monoflo "Ts"?

    Even with the cast iron boiler, would the preferable way to set up the system with the panel radiators be primary/secondary?

    Thanks for all the info !

  • Ironman
    Ironman Member Posts: 7,379
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    It should work fine with monoflo as long as the standard rules are followed. There's an article somewhere the system resource section about diverter Tee systems.
    The boiler can be piped p/s with the current monoflo as the secondary.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,050
    edited December 2019
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    Would it be too much trouble to change from Monoflow to a 2-pipe system? Monoflow became popular because it was relatively inexpensive to install, but it has distinct disadvantages. If you need to drain the system, it can be very difficult to purge the air out of the branches. Secondly, you have to account for the temperature drop as return water mixes with the supply water along the way by sizing up downstream radiators.

    I consider equal supply water temperatures to all the radiators a distinct advantage, no?

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    Peter_26Ironman
  • hot_rod
    hot_rod Member Posts: 22,258
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    I agree with Alan, a properly designed divert or system takes about 12 steps to do properly. You still end up with temperature drop by loops end. Home run with TRVs is close to an ideal system, equal temperature, low pumping costs, near constant circulation, a perfect match for a delta P circulator
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Ironman
  • Peter_26
    Peter_26 Member Posts: 129
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    I can certainly change it to a 2-pipe system. The main off of the boiler and before it splits is 1 1/4 to two 1" loops. I have 3 zones, but two (basement and garage) are not mechanically controlled. By this I mean they have no zone valves that isolate them from the system. By what the SlantFin heat loss calculator estimated, I have:

    Heat Loss:
    Ranch main floor = 50k
    Garage = 10k
    Basement = 15k

    I think I can get away with 1" return for a 2-pipe system, since I am looking at a total flow of approximately 7.5 GPM. Is that cutting it close or would that be fine? The only improvements that have been made are a new insulated garage door and the sill plate was spray foamed. The basement is very warm since the air infiltration is virtually zero now. I am planning on spray foaming all the infiltration points from the attic once it gets warm enough and finish it off with batt insulation.

    Home run? Where can I find diagrams of that? I want to stick with the cast iron boiler, but plan for a condensing when needed.

    Thanks guys!
  • hot_rod
    hot_rod Member Posts: 22,258
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    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Peter_26
    Peter_26 Member Posts: 129
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    Thanks!
  • Peter_26
    Peter_26 Member Posts: 129
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    I like the idea of added comfort, but honestly the ranch we own now compared to the cape cod we had before is very comfortable. There is no room that is noticeably colder. The hottest water is designed to reach the bedrooms first and coolest for living room and kitchen.

    Let's say I over size the fin baseboard for lower SWT and stick with the monoflow system as is could I still benefit from a condensing boiler. since the RWT will be lower? Are there options for condensing boilers that can be directly piped and not worry about P/S? There will still be a benefit from a high efficiency boiler compared to the 30 yr old one I have now, but I want to plan and get the maximum efficiency out of it when it's time to change over.
  • hot_rod
    hot_rod Member Posts: 22,258
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    Most all of the fire tube design boilers can be direct piped, they do specify a minimum flow rate in the installation manual.

    I'd wonder that the last fin tube on the loop would be quite large seeing low SWT on a reduced temperature design. You could run the calc to know that. A modification of the basic hydronic formula.

    T-out= T-in- Q divided by (500X f)

    temperature in
    Q heat removed by emitter in btu/hr.
    500 a constant for water
    f flow rate entering the assembly
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Peter_26
    Peter_26 Member Posts: 129
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    Yeah @hot_rod , don't think that's gonna be a great idea, it's gonna be wall to wall baseboard if I keep the one-pipe monoflo system. The long term plan would be to replace the existing cast iron to condensing boiler, but even that has it's limits.

    After reading the idronics link hot_rod recommended I was looking at the first suggested option of switching to a two-pipe system, Alan suggested, that looks like it could work without a major overhaul of existing piping. So, with the two-pipe system I have two options, direct return and reverse return. The reverse return option looks to be the most promising and it's more of a self balancing configuration.

    Would it be a good idea to pipe it p/s with cast iron boiler?

    Thanks