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Thread: Re-piping the main loop of a cast-iron radiator system

  1. #1

    Default Re-piping the main loop of a cast-iron radiator system

    Hello all,

    I have a monoflow radiator system that heats a basement and two above-ground floors. There are a total of 14 radiators. The system gets the house nice and toasty in the winter.

    The only problem I have is that the main loop in the basement is loooow. The basement ceiling is about 7' but the loop hangs down 14" from the ceiling. It is also set in about four feet from any wall. This makes finishing the basement pointless. I'm a tall guy, I need head clearance!

    I want to raise the main loop up as close to the ceiling as possible and push it out towards the walls. Right now the system uses iron pipe.

    I've gotten estimates from a few plumbers and they all said the same thing - they'll replace the iron pipe in the main loop with 1" copper and connect the main loop to the existing runs to the individual radiators.

    After speaking to the pros this SEEMS like it would be a pretty straightforward project - simply copy the existing main loop layout. Same placement of the monoflow tees, same positioning, direction, etc. Only difference is that it will be 14" higher and closer to the walls.

    Before hiring a pro I'd like to try my hand and doing some a section of this myself. I figure if I am going to be replacing it all anyway it can't hurt to try.

    Are there any potential kinks that I am not considering? Is the job more complicated than it sounds? Is the risk of death higher than zero?

    Any advice is appreciated. Thanks!

  2. #2
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    For the system to work you have to raise the hole loop. If you just raise part of it you will not be able to get all the air out of the system. Keep in mind that all lines should pitch up to your radiators, any traps in the line will hold air and not allow the water to circulate. Be sure to install the copper tees in the same location as the existing tees. It's been a long time since I installed a system like this. If my memory serves me right the tees must be more then 18" apart and no closer then 18" from a change of direction in the main. Also keep in mind that the monoflow tees are directional. There are arrows in the tees that must point in the direction of flow.

    John
    Last edited by johnjh2o1; 09-24-2009 at 07:40 PM.

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default loop

    The other thing you have to consider is the size of the radiators and whether a 1" pipe will supply enough heat for them.

  4. #4

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    John -

    Thanks for the tip about the air getting trapped. I hadn't thought of that. That certainly makes me reconsider my plan for doing this project piecemeal.

    As far as placement of the tees the current system has many, many tees placed close together (8" or less). In one area in particular there are four tees within a two foot section.

    If doing this project myself the plan was to just copy the existing placement of tees. Currently the system gets the house warm, so I didn't even think that the tee placement might be problematic.

    Is this something I should worry about or should I leave well enough alone?

  5. #5
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    If it's working ok then place the tees in the same location that they are now in.

    John

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default tees

    If the system uses two MonoFlo tees for each radiator the placement is not as critical as if you only had one. The reason for the spacing requirement is that the resistance between the two tees HAS to be close to the resistance of the loop to the radiator, or the water will flow straight through and only a portion will be diverted to the radiator.

  7. #7

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    Quote Originally Posted by hj View Post
    If the system uses two MonoFlo tees for each radiator the placement is not as critical as if you only had one. The reason for the spacing requirement is that the resistance between the two tees HAS to be close to the resistance of the loop to the radiator, or the water will flow straight through and only a portion will be diverted to the radiator.
    I spent some time looking over my system this weekend and I noticed that each radiator only uses a single monoflow tee. Upstream is a standard tee (as far as I can tell from an outside inspection), downstream is a monoflo.

    If I was redoing the system in copper I imagine this would still be the model I should follow.

  8. #8
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Quote Originally Posted by jmk823 View Post
    I spent some time looking over my system this weekend and I noticed that each radiator only uses a single monoflow tee. Upstream is a standard tee (as far as I can tell from an outside inspection), downstream is a monoflo.

    If I was redoing the system in copper I imagine this would still be the model I should follow.
    The way to pipe the system is with one monoflow tee on the radiators above the main and two for the ones below.

    John

  9. #9

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    Thanks for all your help. After considering all the associated costs I realized the cost for materials alone would be considerable.

    I brought in a highly reccomended plumber who specializes in this kind of work in my kind of house (ie: old). He reccomended using PEX and a three-manifold system. I like this idea - it completely opens up my basement ceiling. It will also only set me back a little over $4k and be done in a week. Once I take into account how much I would spend myself on materials and time doing the work, this seems like a steal of a price.

    I've heard lots of praise for PEX and a few negative things here and there. It seems especially well suited for this type of project. Any thoughts?

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