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Advice on how to repipe old gravity hot water system

bt_h2o
bt_h2o Member Posts: 10
Hi All,

Plumber here needing to do some heating work as part of a basement remodel.

I need some help on how to properly repipe what was an old gravity hot water system(cast iron radiators). System was recently updated with new boiler and pump added(by someone else) I need to remove 2" supply/returns that hang low in basement and raise piping up as hi as I can get it. What is best way to repipe this? Thanks

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,159
    Since circulation is now provided by a pump, you don't have to worry that much. I'm not a big fan of PEX, but you could repipe in that -- or copper, provided that either one has the room to expand and flex (they both expand a lot more than the old pipes do!). You also need to consider head loss. You will have more head loss if you use smaller pipe. Basically, though, not much different from any hydronic system now.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ironman
    Ironman Member Posts: 7,366
    Dan has a rule of thumb that's always worked for me: Cut the diameter of the large gravity pipe in half and then go one pipe size smaller than that. So, if you have a 2" pipe, 1" is half, - one size =3/4".
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • bt_h2o
    bt_h2o Member Posts: 10
    Do I keep it as 2 pipe (parallel)? Can I make it series? or even monoflo? I thought I had seen in an old post someone saying to run seperate home runs from supply & return risers back to boiler and connect to manifold setup. Does that make sense?
  • JUGHNE
    JUGHNE Member Posts: 11,042
    Can you post pictures of the piping around the boiler as it is now?
  • bt_h2o
    bt_h2o Member Posts: 10
    I don't have any pics currently, sorry. I can try to explain it if it helps. Supply & return are 1 1/4 in and out. Both tie into 2" tees. 2" lines run out and back, one set to front of house one set to back of house. Pump currently on return side. I'm trying to repipe the easiest, quickest way. I'm in MA and need to repipe ideally within 1 day by myself so homeowners will not be without heat
  • Ironman
    Ironman Member Posts: 7,366
    bt_h2o said:

    Do I keep it as 2 pipe (parallel)? Can I make it series? or even monoflo? I thought I had seen in an old post someone saying to run seperate home runs from supply & return risers back to boiler and connect to manifold setup. Does that make sense?

    You need to keepit parallel, whether it's direct or reverse return.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • bt_h2o
    bt_h2o Member Posts: 10
    Ok. Can you explain the difference between direct and reverse return?
  • Paul48
    Paul48 Member Posts: 4,469
    Direct= First out of the boiler, first back to the boiler. Reverse= First out of the boiler, last back to the boiler. Does that make sense?
  • bt_h2o
    bt_h2o Member Posts: 10
    It does. Thanks. Is one way better than the other?
  • SWEI
    SWEI Member Posts: 7,356
    Reverse return is better.
  • Paul48
    Paul48 Member Posts: 4,469
    It helps to balance the heat to the emitters.
  • Ironman
    Ironman Member Posts: 7,366
    Just to clarify: if your system is direct return, (most likely) I would not attempt to re-pipe it into reverse return as that would require re-doing the entire supply main(s). They now start large from the boiler and get smaller as they go on. You would have to reverse that to achieve reverse return.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • bt_h2o
    bt_h2o Member Posts: 10
    Ok. Yes, currently direct return. So, can I run 1" pex from boiler out and back and tie back into risers with either 1" or 3/4 depending on size of riser piping? Or could I run home runs from all supply and return risers back to manifold setup at boiler? Will either work? What makes more sense?
  • Paul48
    Paul48 Member Posts: 4,469
    Did you say....By yourself, in a day?
  • bt_h2o
    bt_h2o Member Posts: 10
    Well that's what the contractor would like. I will be happy in 2 days
  • Paul48
    Paul48 Member Posts: 4,469
    I think you need more hands. I'd make some calls.
    icesailor
  • Ironman
    Ironman Member Posts: 7,366
    sludge said:

    Migrate is the proper term not gravity.... the heated water...heat migrates to the cold water.. heat travels from hot to cold. The 2 inch lines were needed at that time.

    Not to be argumentative, but gravity flow has been the accepted industry term for about 100 years. It is also technically correct: flow is created because the heated water is lighter than the denser cooler water, not because the heated water is migrating. Heat migration could occur in a horizontal line sealed on both ends with no flow occurring. Let a line become air bound and see how little heat migrates once flow is stopped.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    RobGicesailor
  • Weezbo
    Weezbo Member Posts: 6,232
    edited March 2015
    This is Jhonny NY's doing ! :) banging out the video on a gravity conversion like that , ... has the young guys Psyched ,donning the Darth Vader capes and helms lol....
    Have a look at the Video, ( http://forum.heatinghelp.com/discussion/153911/8-hours-of-boiler-work-in-60-seconds#latest )
    bt_H20 , while it is not exactly what you are doing , it is pretty close . Where you see the 4 pipes somewhat represents what you will have when you come away to the boiler . The pipes out to the front would be by 90's and the two to the back of the house the same after you lose the "T"
    i'd favor some T's for purge valves , valves for circs, T's for temp gauges , check valves , in your install ..As you have no pics making certain things are flowing first ,
    might not be a bad idea either.
    You might have to revise when you intend to : manage to test the system as it now is, pipe this , test it ,refill the system ,fire it, go through the first cycle,
    Check gauges ,stack temps etc... bang in a by pass you may have blown by.. Go with "I will have it done by Thursday." that always sounds good.

    Good Luck . Honestly , might want do get a few Auxiliary electric heaters lined up ahead of time also.Just "In case" Thursday next week happens to be when you are done.

    Weezbo.
  • Henry
    Henry Member Posts: 998
    Over the years we have done a few of these. They take up to 5 days depending on the number of rads.The easiest system for your 2 inch mains is to do a 1 1/4 monoflow sytem. You can save time by preparing the monoflow line first and then hooking up the rads.
  • icesailor
    icesailor Member Posts: 7,265
    Ironman said:

    Dan has a rule of thumb that's always worked for me: Cut the diameter of the large gravity pipe in half and then go one pipe size smaller than that. So, if you have a 2" pipe, 1" is half, - one size =3/4".

    I don't know Dan's rule, and I'm not quibbling, but "Pipes Increase As Do Their Squares", Which means that it takes 4-1" pipes to equal the volume and area of a 2" pipe. It takes 4-3/4" pipes to equal a 1 1/2" pipe. If you replace a 2" pipe with a 1" pipe, you have reduced the area/volume by 200%. Even more if you again reduce it to 3/4".

    I'm finding that there are new rules in hydronic piping. They must work for someone. All contrary to anything I ever learned or practiced.

    In Massachusetts, a new Apprentice Plumber must register, do a 5 year apprenticeship, and to a total of 500 hours, 100 hours per year at an approved plumbing theory class/school, and take a test given by the State Board of Plumbing Examiners and get a passing grade of 70%. If after all that, and an apprentice answered a question that comes to that conclusion, that dividing a 2" pipe in half will be equal to a single 1" pipe, I assure you that the question will be marked wrong.

    Just saying.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,452
    Ice, the pipes are sized for gravity it's pumped now. Your right of course about the pipe size but now we have a pump to overcome the resistance of the piping.
  • icesailor
    icesailor Member Posts: 7,265
    I know that.

    I was also told that the reason for the big pipes was two fold. Less surface area in the larger pipe, and the larger volume of water had less resistance to the flow. So that actual flow through the pipe, slowly, in volume, was the same as being forced faster through a smaller pipe. In the end, what went out of the boiler, and what came back was the same. Whether flowing by the difference in water temperature causing circulation or that a pump did it. Everything had a resistance value, that determined the overall size of the pipe and how much it could carry.

    Everything changed when some weren't watching.