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radiant heat installation

ckib | Posted in Construction Techniques on January 31, 2005 05:55am

Hi,

I just had radiant heat installed in my house, specifically, under the first floor.  The radiant heating tubes (pex) were stapled up to the basement ceiling.  At one end of the bay the tubes make a U turn.  At the other end of the house the tubes drop down along and under each floor joist.  The plumber said he did not drill holes in the joists because the code specifies that holes cannot be drilled within 3 feet from the end of the house … and that would compromise the strength of the joist.  Is this true?  I’ve read a little about radiant heat installation and it always looks like the holes where the pex tubing passes through are very close to the end of the bay.  Also, the insulation company tells me I should insulate the pex tubing that drops down along and under each floor joist before the insulation is installed in the bays.  The plumber says it’s not necessary as not much heat will be lost.  Any advice is welcome!

Thanks.

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  1. User avater
    johnnyd | Jan 31, 2005 07:22pm | #1

    Whether the PEX goes through or under/around the joist is a smaller issue than some others:

    Those plates look like they don't crimp around the PEX, but maybe the picture doesn't really show that well.  The purpose of the plate is to get the heat conducting directly to the sub floor better than just air...how close are those plates spaced, and are there plates on both the supply and return side of the loops?  I'm thinking you may not have enough plates.  Consider getting some more channeled plates and fasten them up to the subfloor, with the grooves holding the PEX as tight as possible. Providing the loops are in the right length range and the whole system is spec'd to a pretty detailed heat loss calc, I don't think you could ever have too many plates.

    Is that band joist on an exterior wall?  You'll really have to be diligent about insulating there...between the tubes and the band joist...I would suggest at least blocks of extruded foamed in place or better yet expanding foam sprayed in to seal that up.

    When you insulate the joist space I think most would recommend leaving a 2" space between the top of the insulation and bottom of subfloor.

    How long are those loops? Should be 250' max for each loop with 1/2" PEX.

    Is this same plumber going to install the rest of the system?  You might want to get educated on heat source, circulation pump, flow control, piping, zoning, and zone control theory and have a chat with him about those things before he does them.

    Whether or not to slip insulation over the PEX where it loops under the joists has more to do with how warm you want your basement to be.

    Something else bugs me about this...are the main supply tubes that come from the manifold ends the same size as the flooring supply tubes?  Any way to control that flow besides the ball valves?  Maybe this is just a way to warm the floors rather than serve as a primary heat source for those rooms.

    Also what's up with that big white (electric) wire that's kind of dangling in space? Temporary or permanent?



    Edited 1/31/2005 11:32 am ET by johnnyd

    1. ckib | Feb 03, 2005 05:16am | #3

      It looks to me like the plates grip the tubes pretty well.

      The insulation contractor is planning to use something called "blockers" at the ends of the bays, on the exterior walls.  And yes, he said that the insulation will be installed 2" below the pex.

      Sadly, the job is complete.  I trusted the plumber to install the radiant without educating myself first on components, installation methods, etc.  I've learned a few good lessons on this project ... ones that I hope not to repeat! 

      I believe the plumber said the tubes were 3/16.  Not sure if they are all the same size.  Is that important?

      This is the primary heat source for my first floor, except for the living room, which remains FHW.

      I don't know if there is any other way to control the flow.  I asked the GC and he started talking about controling the temperature and that there are other ways to do that.  Not sure if he was talking about the same thing.  Right now the plumber has the water temp turned way up to compensate for the lack of insulation (MA winter).  But when the temp rises above 35 degrees outside, it starts to feel like a sauna inside!  The insulation is getting installed next week, so hopefully we get some control over the temp soon.

      Oops, that long extension cord is ... well ... semi-permanent!  I'll have to do something about that too.

      Thanks.

       

       

       

  2. csnow | Jan 31, 2005 07:32pm | #2

    "The plumber said he did not drill holes in the joists because the code specifies that holes cannot be drilled within 3 feet from the end of the house ... and that would compromise the strength of the joist.  Is this true?"

    Doubt it.  Generally safer to drill near ends.  These are small holes, and it makes insulating a bit messy.  OTOH, it's not that bad the way it is.  I would not leave those wayward nail points near the PEX.  Probably will not puncture, but bad form.

    "Also, the insulation company tells me I should insulate the pex tubing that drops down along and under each floor joist before the insulation is installed in the bays.  The plumber says it's not necessary as not much heat will be lost.  Any advice is welcome!"

    True, not a great deal of heatloss. PEX should be protected from sunlight though.  Is that a real window?  I would insulate with foam pipe wrap for protection.

     

    1. ckib | Feb 03, 2005 05:18am | #4

      Thanks. 

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