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Radiant Heat Questions

Stone Member Posts: 3
After having some under tile electric heat for a few years, I've decided to put in some aluminum staple up pex between the joists in the basement.

I currently have forced air furnace, however I liked the under tile heat so much, that I wanted the rest of the 1st floor to have radiant heat as well.

I already have a Hydroshark electric SH3-12 boiler. I'm in the planning stages so I have a few questions.

<a href="http://www.hydro-smartwholesale.com/Images/HydroShark3-4PanelBrochure.pdf">http://www.hydro-smartwholesale.com/Images/HydroShark3-4PanelBrochure.pdf</a>

The Hydroshark Boiler is 12KW and is rated 40,000 BTU with max temp of 140 degrees

The approx total sq footage to heat is 1160 divided into two zones (calculated to require about 30000 BTUs) -

Zone 1: Family Room 12" on center joist (carpet) 330 sq feet (vaulted ceilings, lots of windows)

Zone 2: Master Bedroom 12" on center joist (carpet), Dining Room 12" on center (3/4" hardwood) Living Room 16" on center (3/4" Hardwood) for a total of 830 sq feet

Do I absolutely need a primary loop for my boiler for two zones?

Because my joists are 12" on center as well as 16" on center, I feel that running two 1/2" PEX tubing per bay would be difficult on the 12" on center joist bays. Would running a larger PEX tube as a single run per bay with the aluminum plate staple up be effective?

I've seen a 7/8" pex tube made for underfloor staple up heating with matching aluminum plates as an alternative which only requires single joist bay runs.

<a href="http://radiantcompany.com/details/joists.shtml">http://radiantcompany.com/details/joists.shtml</a>

I was wondering if anyone had any opinions/advice on the 7/8" PEX

Additionally, do you put the reflective radiant barrier under the aluminum plates with a 2" gap? I've read that dust collects and renders the reflective barrier ineffective. Of course I'll put fiberglass insulation after that.

What temp do you generally run the boiler? 120 degrees?

Do the aluminum plates create alot of noise during warm-ups?

Thanks in advance.


  • Zman
    Zman Member Posts: 7,434
    Cart before the horse...

    The first thing you need is an accurate room by room heat loss calculation. Next, I would determine your target water temp. After that it would make sense to look at the different options regarding panel assemblies. You  can't use the generic charts supplied by a radiant supplier and expect to get a comfortable system.

    The details provided on the radiant companies website are horrible. If you are looking for a noisy ,imbalanced install they will help you get there.

    I would look at the details on http://www.uponor-usa.com/ website after you do a heat loss.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kcopp
    kcopp Member Posts: 4,092
    Carl is right....

    to say start w/ the heatloss. Furthermore the 7/8" tubing is a farce..... one company said to do this years ago and generally speaking it did not work well.... lots of unhappy people posted similar non working installs here. 1/2" or 3/8" tubing w/ plates and minimum r-20 insulation is the way to go.... more work, more time, more money up front but  you will be better off.
  • SWEI
    SWEI Member Posts: 7,356
    7/8 tubing

    I suspect an overwhelming majority of radiant professionals would consider the advice offered on that site as borderline mechanical malpractice.

    The physics are not all that complex, but there are still an unfortunate number of manufacturers, dealers, and installers out there who either have not bothered to learn them or simply they they don't matter.  Caveat emptor.
  • HFC
    HFC Member Posts: 29
    12" Joist Bays Are Not A Problem

    I had no problems running pulling Wirsbo 1/2” hePEX

    in 200 plus feet of joist bays and maintaining 8” center to center in the bays that

    were 11-1/2” and larger. The bay in the pictures below is 11-1/2” wide.

  • Stone
    Stone Member Posts: 3
    7/8" PEX

    Thanks for the feedback. So absolutely avoid the 7/8" PEX?

    The logic given by the company pushing the 7/8" PEX seems like it should work, but the Wallies says "NO WAY". I'm curious as to what result would one get? Alot of cold spots?
  • SWEI
    SWEI Member Posts: 7,356

    The goal is even heat across the floor surface.  For a given average temperature, tubing on wider centers will require a higher fluid temp, which makes for hotter hot spots (hot stripes, really.)  Smaller tubing on narrower centers will give more even heat and do so using a lower fluid temperature, which will increase boiler efficiency (on a mod/con) or allow more weeks of active solar heating in that application.  Too small and pipe friction becomes a problem - 3/8" and 1/2" work quite well.

    Proper use of extruded aluminum plates (or the new graphite ones) will further increase transmission efficiency by about 75%.
  • Zman
    Zman Member Posts: 7,434
    Say no

    Any company that tries to do radiant with out even talking about heat loss should be avoided. It is not hard to do a calculation and it is the cornerstone of your system.

    You need to define "it works". I am certain that the systems advertised "work".That is they provide some heat, some of the time.

     If you spend the time to do an accurate time now you will be happier in the long term.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Stone
    Stone Member Posts: 3

    any opinions on onix - seems that install would be easier and not having to deal with plates
This discussion has been closed.