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replacing heating distribution pipes with pex

10kREDLINE Member Posts: 15
this may make for an interesting read for some. i recently employed a plumbing and heating contractor for part of my basement finishing project.  my heating system consisted of a Utica MGB-175-HD boiler (standard cast iron 175k btu, net output 143k), with a two pipe (approx 2" each) reverse return system pushed by a grundfos 15-58, spirovent for air removal, etc. i put the system together when we bought this house and i thought it worked pretty well. 

now it comes time to finish the basement, and those big pipes hang low so it's time to get rid of them says the heating contractor, who says we're going to re run everything in pex through the floor joists above ( this is a 2.5 story colonial with a full unfinshed basement, ceiling almost ft). i say lets go for it.

<strong>here's the interesting part.</strong> now the pipes are cut out, and the contractor wants to run the first and second floor on individual zones, which is fine.  however, he wants to run each floor in series, individually by floor, from radiator to radiator using 1/2" pex.  the radiation in my house specifically the first and second floor, are all cast iron with average dimensions of 50" long, 4" deep and 26" high and there are 3 of these on each floor, plus two more half this size on each floor. im not exactly sure of the btu output of these monsters but im under the impression that 1/2" pex can only carry about 15k btu.

after reading up on the wall (thanks to you guys) im thinking that home runs might be in order, but i need some input, and pretty quick so i can stop this if need be.  thanks in advance, john.


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Short cycling?

    If you have a lot of small zones, what will you do to prevent short cycling if only one zone calls for heat?
  • icesailor
    icesailor Member Posts: 7,265
    Eat & Greet:

    Another "expert" ("X" being an unknown quantity and "spert" being a drip under pressure).

    DH wrote a book called "Dead Men's Steam Book". He now needs to write on called Dead (and old living) Men's Hydronic book. To retrain these clowns that get their information from the local supply house that has an eat and greet with the PEX sales-persons

    You had a system that worked very well. Now, you will have a system that will marginally work if at all.

    I'll bet that if you asked the "hydronics expert" to draw an example of ten heat emitting units piped as (1)  In Series, (2) A Direct Return, and (3) A Reverse Return, he couldn't do it and explain how and why they worked. Also, the advantages of each over the others.

    They need to be tested and licensed like Plumbers in Massachusetts are.

    The AC/HVAC guys are loosing their mind because they are going to have to start testing their duct work for tightness now under the building code and Sheet Metal Contractors Law. DUH!!!  Most of us Wet-head/Plumbers have been testing out piping for years.

    And the guy will probably intend to series loop all the radiators with 1/2" PEX. Hopefully, HE-PEX 

    (Shaking my head in disbelief)
  • 10kREDLINE
    10kREDLINE Member Posts: 15

    Would the system really short cycle with 5 larger radiators on each zone? As it is now i get a hotter second floor and decent first floor, the thermostat is located on the first floor. The new setup will involve thermostats in the finished basement, one on the first floor and one on the second floor.

    Now that my thought of "good luck with 1/2 inch pex in series" has been confirmed, i would like to consider home runs from manifolds using 1/2" pex (oxygen barrier) , each manifold controlled by a zone valve. Each manifold representing a floor. Thoughts?
  • Empire_2
    Empire_2 Member Posts: 2,343
    edited May 2012
    WOW...Hope you get it straight before final.

    1/2" pex for each floor? All radiators in series?  Find a local contractor to do this right or you'll regret it.  The boiler itself must move 13.5 GPM so 1/2" pex is a no go.......Total up your radiators BTU/HR and see what size boiler is required.  Go from there.  The whole name of the game is to get your 20* "delta-T" between supply and return.  These numbers can vary, but that is a starting point.  You can slam water through the 1/2" pex, but velocity will be causing incredible sound.  Not sure what he was thinking when recommending 1/2".

    Mike T.
  • Slimpickins
    Slimpickins Member Posts: 323
    Home runs yes

    Yes by all means do a home run system. Zone valves are so 1970's and since you have to adapt the radiator valve anyway, you could install a TRV (thermostatic radiator valve) and control each rad individually and do away with running thermostat wires and thermostats and transformers. If you feel you must keep the existing boiler, this is what I would recommend.  Install ya a EMC smart pump for your heat loop, a Tekmar 356 mixing control for injection pumping, outdoor reset and boiler protection and you're in comfort heaven. IMHO, this is the only way to go for comfort, safety and simplification. 
  • 10kREDLINE
    10kREDLINE Member Posts: 15
    To simplickens

    Thank you for your recommendation on the trv's and the home runs. I plan on keeping my boiler as its only about 4 years young. Would the zone valve / manifold concept be accepatable for its function? Im trying to be careful where i spend cash, i still have to finish the rest of the basement.
  • Slimpickins
    Slimpickins Member Posts: 323
    zone valves vs. TRV

    if you do home runs you're still gonna need zone valves for each rad and they're a bit cheaper than a good quality TRV. I think your problem is finding someone to employ this technology and it doesn't sound like your contractor has that knowledge. It's hard for plumbers to gasp non zone valve systems and many do not understand the consequences of not having boiler protection with cast iron boilers. Personally I cringe at the thought of using pex on constant high temperature applications. It's kinda too bad you're this far along in your project and hopefully your contractor won't mind learning a better way to do something. So yes, you can use zone valves but a means of protecting the boiler from low return temps are a must. I'll be off the computer for a few days and I'm sure others on here will help with any of your questions. Good luck!
  • CMadatMe
    CMadatMe Member Posts: 3,085
    Read This

    You'll know more then this contractor will ever learn. Page 19 is what you want to do. Heck homerun and you might be able to get away with 3/8" pex. Make sure a heat loss is done as well as calculate the capable btu/hr output of the rads. You may find you don't need 180 degree water to heat this place. Also would have to make sure we protect that boiler if we are going to add outdoor reset into the equation.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • 10kREDLINE
    10kREDLINE Member Posts: 15
    To chris

    Im going to read that chris thanks. I hadnt considered ODR, and i may leave it out of the picture for the immediate future. But i wont rule it out. I will incorporate the esbe valve or another mixing device for boiler protection. Can i plumb the pex manifolds right off the zone valves as i had planned?
  • Henry
    Henry Member Posts: 988

    We have done several conversions from reverse return and gravity to a monoflow system to increase headroom in the basement. It is the most cost efective method. You should use outdoor reset and have a bypass to protect the boiler.

    Please loose the phone number of the numbnut who said to use pex! Be aware that even if you use a manifold to pipe each individual radiator, you can have air pockets with pex!
  • SWEI
    SWEI Member Posts: 7,356
    outdoor reset

    Is so important to both comfort and savings that I'd probably implement it first - even if I had to defer putting TRVs on the radiators.  With a properly tuned reset curve, the system circulator will run nearly 24x7 and the boiler (even a conventional one) will run more efficiently.  The required near-boiler piping changes are much easier to make now than later.  You can install TRVs and even change out a conventional circ for a smart circ with minimal labor later - perhaps even DIY if you're capable.  Depending on the actual heat loss and the boiler sizing, a buffer tank might be in order.  They also make excellent hydraulic separators.
  • Zman
    Zman Member Posts: 7,005

    I really like the system Slimpickins described in his first post.

     If you can I would certainly home run the rads.

    If TRVs and outdoor reset are not in the budget today, You can manifold several rads together and have the floor by floor zoning you describe. You will have done the infrastructure needed for the perfect system down the road.Eventually a modcon boiler.

    If your contractor was seriously planning 1/2" in series, I am not sure I would let him back in the house.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • 10kREDLINE
    10kREDLINE Member Posts: 15
    Thanks for all of the replies

    The outdoor reset and trv's are out of the budget for now. You guys are phenomenal with the advice and opinions. I'm going to do the manifolds and home runs to each radiator, and zone the rads by floor. Anyone have any bypass advice?
  • Zman
    Zman Member Posts: 7,005
    Are you?

    Are you looking for a boiler bipass to prevent condensation, or a diff pressure bipass on the manifolds?

    How is it piped now?

    Due you know the minimum flow for your boiler?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • gennady
    gennady Member Posts: 830
    edited May 2012

    In my opinion, if you went with atmospheric standard efficiency boiler, do primary/secondary piping, on system side install variably frequency drive pump in auto mode, install TRV, on all radiators, you can pipe radiators with manifolds or any way you want but if in series use bypass line with properly sized piping, install outdoor reset controlled valve on boiler side, outdoor reset system sensor install at system pump discharge. you will use boiler as a buffer tank as well in this configuration. do not use zone valves or thermostats in this configuration, or install 1 thermostat in coldest room, but you must not install TRV on radiators in this room. And using 1/2 pex the way you described is a very bad idea. you have to find a professional , not a handyman to do your heating system.
  • 10kREDLINE
    10kREDLINE Member Posts: 15

    Im considering the pressure differential bypass due to the zone valves, but im definately doing a bypass to prevent too, uch cold water from coming back to the boiler.. Does this need to be a concern still due to getting rid of the large diameter pipes and replacing them with 1/2 inch pex, the water content has been reduced significantly.
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