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Joist heating replacing CI rad

JimmyJam
JimmyJam Member Posts: 78
I need a little design assistance please!
I have an older lady remodeling her kitchen cabinets which requires removal of a CI rad to allow for new cabinets. The system was originally a 2 pipe gravity system, the kitchen happens to be on the end of the mains and I am thinking about joist heating as an option. My question is how am i going to plumb into existing system without altering flow to existing rads? Would I pull off pipe going to kitchen rad and return at boiler with paralled pump? Ideally I would plumb in P/S system with independant zone however budget is a concern here. I really appreciate any input!!!!!!

Comments

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    My question is how am i going to plumb into existing system without altering flow to existing rads?

    By keeping head loss through the new portion VERY low and using the existing TRUE supply temp in the mains--NOT the aquastat setting! Likely impractical with underfloor heating as you'll likely need a significantly higher supply temperature than currently available.

    Any space for a wall-hung panel radiator? Custom cabinet design allowing you to build in some form of radiator?
  • JimmyJam
    JimmyJam Member Posts: 78
    Thanks Mike

    I haven't been to this house for a couple of years and will have to look into a panel rad, when you say keep head loss VERY low does that mean you are recommending using existing system circulator for new joist system? I was leaning towards 3/8" HePex and joist trak plates which would have around a 25-30BTUH ouput with a mean temp around 150, however I would have to install independant circulator for this loop I'm sure. Any thoughts about fin tube between joists? I would think that would have a low enough pressure drop but not sure how well this would work?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    If you installed another circulator at the existing supply or return connection to the radiator you may well upset the flow balance in the rest of the system. Believe you'd be a lot better off going primary/secondary but you mentioned that budget would prevent doing it the way you would really like to do...

    I kind of doubt that you have 150 degree water available (even at design conditions) in a converted gravity system, so you're again faced with significant changes in the near-boiler piping and controls.

    Zero experience with fin tube radiation inside of floor joist cavities--might work at the temps currently available but might not... If you wanted to do this using the current rad connections, believe you'd run supply/return manifolds (same size as current rad branch piping) in reverse-return with each fin tube having its own connections to the manifold. Flow shouldn't be an issue, but balance???
  • Steamhead
    Steamhead Member Posts: 17,309
    I'd try to find

    a radiator of a different shape but similar capacity that will fit in an available space.

    The water velocity in the big pipes of a gravity conversion is very low. Therefore you must keep the supply and return lines the same size as they are now. If you try to reduce pipe size, you'll end up with little or no flow to that radiator.

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  • Paul Pollets
    Paul Pollets Member Posts: 3,662
    Oventrop UniBox

    The Oventrop UniBox will allow you to add a zone of radiant heat using the old radiator stubouts. You may not have to change your pump using 3/8" PEX and plates.
    It's the easiest way to add a RFH zone with existing radiators without having to add a mixing station or another pump.

    See the following for more info:

    http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=15776&mc=13

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