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radiant hydronic heating system design

bradley Member Posts: 18
It was with great interest that I came across this website.  I really enjoyed the thread about designing a slant fin baseboard system.  With this thread in mind I would like to ask if I could submit a diagram of a system I am working on and get comments and suggestions.  I live in a small town in rural Ontario and have had two very disappointing experiences with heating contractors.  I now own most of the parts for a radiant system but as yet have no operational system.  Two installs and two tear downs and now I am going to do this thing myself, mainly because I have no choice (no more money and no more trust).  I thought I should ask first if it was all right to solicit detailed design ideas.


  • CMadatMe
    CMadatMe Member Posts: 3,086

    Sure. Let's start with what's the heat loss and the radiant application?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • bradley
    bradley Member Posts: 18

    ok!  The heat loss is 21000.  Small (740 sq ft house), well insulated (r40 roof, icf walls r28, r 30 under slab plus r15 perimeter horizontal wing insulation.  Four heating zones with individual flow controllers.  The question I have so far are:  1) do I need an air vent on the boiler?  2) do I need a mixing valve?  3) where should I put shut off valves?  4)  the diagram shows a make up water supply for use with water as a heating medium.  If I use glycol, do I, and how do I, provide make up fluid?  Any more thoughts, comments, problems much appreciated.
  • Gordan
    Gordan Member Posts: 891
    A couple of things...

    Disclaimer: I'm not a pro.

    What are your design indoor/outdoor temps? Heat loss seems big for such a small, well-insulated structure.

    What will be your min and max temperatures for the system? Judging by the amount of piping you'll have, a #15 tank would be plenty.

    Have you consulted the installation manual? They spec a different flow switch (FS4-3T3-1) for this boiler. Yes, they suggest an air vent for the boiler. They also have some multi-zone piping strategies to insure that you can get adequate flow through the boiler when some zones are shut off.

    Why are you considering glycol? Will the structure be left unattended/unheated? If so, what will prevent your plumbing from freezing? You may want to check with the manufacturer for any caveats regarding use with glycol. Also, the flow switch may behave slightly differently with glycol; doesn't hurt to check.
  • bradley
    bradley Member Posts: 18
    edited August 2010
    thanks for the reply

    Indoor temp 70 f  Outdoor -18 f.  To clarify, the house is 1.5 stories, so there are 12 ' walls to account for.  Heat loss was done by three different people.

    Max. system temp will be 150.  I have the 60 tank already from the first botched install.  Do I need a smaller one?

    I see the recommended flow switch in the manual.  Don't know why the original installer used the different one.  I think he was designing a fairly complicated system.  Can I use the one I have or should I get the recommended one?

    I was planning on using glycol simply because that is what was originally planned.  I see in the manual recommendations for those who use well water, and also hard water.  I can do this.  But is there any advantage to using glycol, or would you recommend water?

    I also see the recommended bypass piping arrangement.  I had not even considered that.  Thanks!  there has to be more that I am missing.
  • zacmobile
    zacmobile Member Posts: 211
    edited August 2010
    botched heating

    1) I believe the monitron boilers have a spot on them for an air vent, I would put one on.

    2) the boiler output temperature should be able to track the system demands

    accurately enough and there is no need for low temperature protection

    with an electric boiler. so you do not need a mixing valve.

    3) put shut-off valves on either side of any pump (you can get special isolation flanges for this, highly recommended!) and put one on the boiler return main and tees with drains on either side of it for filling/purging the system.

    4) make-up water would be provided by a boiler fill/back flow preventer

    assembly (see installation manual) if you choose not to have on I would

    put in a low water cut-off switch. although I suppose the flow switch

    would acheive the same thing.

    5) the only good thing about glycol is that it doesn't freeze, it does require more maintainance, you must check the PH at least once a year to make sure it hasn't gone off. Also it is a slightly poorer heat transfer medium than water and requires slightly more pumping power to move it around, so unless you plan on being away and leaving the home unattended for extended periods of time (I would say a week+ with your tight construction) I would give it a pass and just use water with the appropriate amount of hydronic corrosion inihibitor.

    I would go with whatever the manufacturer recommends for installation piping, the only thing I would do differently is use a pressure activated bypass valve in lieu of a static throttling valve on the bypass, you will keep the system flows constant that way.

    best of luck!

    ps: why is your system temperature 150? I would be suprised if you required more than 110. and what is the "60 tank" you're referring to?
  • bradley
    bradley Member Posts: 18
    edited August 2010
    The boiler temp.

    was set by the original installer.  I guess he figured he needed a mixing valve because the boiler temp was set so high?  I don't know.  I just know that I have a mixing valve for some reason. I am having a hard time figuring out he set things up the way he did.  The tank I'm referring to is an Amtrol Extrol 60 diaphragm expansion tank.  Again, these are parts that I already own and are sitting in a big cardboard box until you guys so graciously hep me muddle through this installation.  Gordon (previous post) figured I only needed a # 15 tank.  I'm gonna guess that a 15 is smaller than a 60,  but what do these numbers mean?

    My boiler manual gives no instructions for feed water.  I took my design from the watts feed water pressure regulator installation instructions.

    Also, sorry about the attachment from my second post.  It appears to be rotated 90 degrees and I can't get it oriented properly.  This makes it hard to read I know. 
  • zacmobile
    zacmobile Member Posts: 211
    edited August 2010

    The numbers on those tanks don't mean anything they are just the manufacturers model designations, the #15 is a 2 gallon tank & the #60 is 8 gallons I believe.

    I found this manual on slant/fin's site, they do show a make-up water connection (called fill valve) on their diagrams, fig.5 on page 5 would most fit your application I think.

This discussion has been closed.