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Thread: New radiator not getting water supply.

  1. #1
    DIY Junior Member uwtriguy's Avatar
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    Default New radiator not getting water supply.

    I recently added a new radiator to my hot water heat system via existing (once used by former owners) stubs on the 1" chase pipe around my basement. From what I gathered studying my system and the old pipes still hanging in the crawl space is the pipes feeding the system off of the chase are 1/2" (a mix between galvanized and black pipe). Although the supply stub is 3/4", the old pipe is 1/2" so there must have been a reducer that was removed when they took the system out. I used 1/2" PEX for simplicity when adding the new radiator to the old location. I reduced from the 3/4" supply tee to 1/2" and the return line was already set for 1/2". The return tee is a MonFlo tee. The problem I'm having is the flow from the chase is not traveling all the way through the new radiator through the 1/2" PEX. It has been 30 minutes + and the radiator valve is just now warming up.

    Another thing to add: By the looks of the old system is was likely a 2-3 foot long, tall radiator and I am adding an 11' long Crane baseboard (cast iron). The run from the chase to the supply side isn't too much longer (3') and the run from the return to the chase is the same as the old system. There is a galvanized union close to the supply tee on the chase that could have been used to remove an old MonFlo tee when the system was changed but I would have no way of telling.

    My thoughts and questions questions would be this:

    1. The new radiator inlets are 3/4" so I should not have reduced going up to them in the first place.

    2. 1/2" PEX ID is much smaller than 1/2 galvanized ID. Maybe I need to go to 3/4" pex on the supply side.

    3. Go to 3/4 PEX on both sides and reduce it into the1/2" return tee.

    4. Use the union on the chase to pull off the supply tee and add a MonFlo tee in its place to force more water to the radiator.

    5. Is there a certain distance that the supply and return stubs need to be away from each other depending on the length of the radiator it is installing? Currently the two stubs are roughly 6' apart including a 90 bend. Again the new radiator is 11' long.

    Any thoughts?

    Thanks!
    Last edited by uwtriguy; 11-14-2010 at 09:20 AM.

  2. #2
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Sounds like air. Did you put a vent on the new baseboard? There should be a i/8" tapping in the baseboard for the purpose of installing a key or coin vent.

    John

  3. #3
    DIY Junior Member uwtriguy's Avatar
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    Yep, have a Taco vent on it. The system filled back up including the new radiator, just not pushing water through it when the system pump is running. I did discover that another piece of Crane baseboard in my house (3' in the bathroom) is supplied by 3/4" pipe. The tapping on the Crane radiators are all 3/4". I'd still like to hear other ideas before I drain the system and increase pipe size. If I do indeed increase PEX size will 3/4" Pex be large enough? Thanks again.

  4. #4
    DIY Junior Member uwtriguy's Avatar
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    Quote Originally Posted by johnjh2o1 View Post
    Sounds like air. Did you put a vent on the new baseboard? There should be a i/8" tapping in the baseboard for the purpose of installing a key or coin vent.

    John
    The 1/8" tapping is actually tapped into a 3/4" plug with a 1/8" tapped hole.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    You generally need a monoflow T on each end. Without one on the inlet, there's nothing to push water into that loop. 1/2" pex will restrict the maximum flow, but if the supply is also 1/2", not by all that much.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Quote Originally Posted by jadnashua View Post
    You generally need a monoflow T on each end. Without one on the inlet, there's nothing to push water into that loop. 1/2" pex will restrict the maximum flow, but if the supply is also 1/2", not by all that much.
    Most one pipe systems are done with one monoflow tee. The only time two are needed is if the baseboard or radiator is below the main.

    John

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I think the monoflow T needs to be on the inlet side, not the outlet, or you need two of them. You need something to force the hot water into the thing, otherwise, it will just bypass it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    DIY Junior Member uwtriguy's Avatar
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    Pulled the lines out. Switched over to 3/4" PEX from supply to radiator and 3/4" from radiator return to chase where there as 3/4"->1/2" reducer directly on the MonFlo tee at the chase. Still no water flowing to the new radiator. I've purged all of the water out of the system from each radiator. Still working on it.

  9. #9
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Quote Originally Posted by jadnashua View Post
    I think the monoflow T needs to be on the inlet side, not the outlet, or you need two of them. You need something to force the hot water into the thing, otherwise, it will just bypass it.
    Monoflow T's work on a venturi action, they can be used on the supply side but work much better on the return. If they don't work on the return side then there are hundreds of systems that I installed that are not working.

    John


    John

  10. #10
    DIY Junior Member uwtriguy's Avatar
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    The MonFlo is on the supply side and was already there when I started this project with a 1/2" branch connected to it that was capped right at a hole in the joist where a pipe used to go through. All I did in this process was tap into current stubs with PEX and hook that up to the radiator. Now I'm just scratching my head.

  11. #11
    DIY Junior Member uwtriguy's Avatar
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    So doing some research I see that you should always have pipes sloping back to the boiler. I do have some upward movement of the return PEX when it comes back to the chase pipe. I'm going to try and fix that soon and see if that helps.

  12. #12
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Quote Originally Posted by uwtriguy View Post
    So doing some research I see that you should always have pipes sloping back to the boiler. I do have some upward movement of the return PEX when it comes back to the chase pipe. I'm going to try and fix that soon and see if that helps.
    That is your problem. You have air trapped in the line that is sloping in the wrong direction.

    John

  13. #13
    DIY Junior Member uwtriguy's Avatar
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    Fantastic. Re-piped it again and still nothing. Time for a second monoflo. Only problem I just spent an hour online trying to source a 1" x 3/4" or 1"x1/2" threaded black tee. Nothing to find!!!

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