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Thread: My in-joist radiant needs HELP!

  1. #1
    DIY Junior Member russer's Avatar
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    Exclamation My in-joist radiant needs HELP!

    I have installed 1/2" lines in the entire 2100 sf of a bungalow. One line per joist space, 250 ft runs, 6 runs, insulated with foil faced fiberglass. With all lines open the temperature in the house if fairly consistant except the ensuite. when the rest of the house is at 19-20 deg the ensuite is 14 and the master is 18. The master and ensuite are at the southwest and northwest respectively. The joist space under the master and ensuite have extra insulation (roxul) and the ensuite has extra aluminum radiators. R-50 in the attic. I am stumped. The kitchen has limestone flooring, ensuite is porcelain, the rest is hardwood. The limestone is nice and warm, hardwood is almost as warm, The porcelain is very cold. The return lines from the master and ensuite seem to come back a bit warmer that the others. The boiler is opposite end from the master but I have the supply and returns wraped in foil/fiberglass between the boiler and heating zone. Help!

  2. #2
    General Engineering Contractor ballvalve's Avatar
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    Just add some ballvalves [ which you must have now on the manifold?] and adjust the flow to the cool areas over a few days until you get what you want.

    You could raise the water temp a bit and reduce flow to the warm areas, pushing more water into the cool zones.

    I have 6 zones, and fiddled with them for a week or so until everything got close to what was wanted. Some zones I leave full off or on if it gets extremely cold.

  3. #3
    DIY Junior Member russer's Avatar
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    Thanks Ballvalve, but I've been turning valves and adjusting water temp for over a month now and I just can't get the heat out of the lines and into the floor in the ensuite. The rest of the house works fine. Even when I close the valves on all other lines, the water goes out hot and comes back hot. It takes the chill off as it would be much colder in there with no heating, but you can't feel any heat in the floor.

  4. #4
    General Engineering Contractor ballvalve's Avatar
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    Seems like the only thing left is a flow restriction. Something IN the ballvalve or pipe, or god forbid, a kink.

    Perhaps you will need to disconnect the return line and inspect the valves and do a test of output from that line when all the other valves are closed. Possible back flush the loop also. Sounds like low flow to one zone.

    My radiant system stopped heating because a tiny piece of rubber from a failing washer got stuck in the checkvalve [open system]

    Home made or pre built manifold?

  5. #5
    In the Trades Tom Sawyer's Avatar
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    Need to know how the boiler and system is piped. What are you getting for delta T's at each loop return and delta T overall at the boiler return. Are your circultors large enough and in the proper position? There are a host of things that can be the cause of your problem.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    You can only extract so much heat per volume and length of run, so without knowing exactly your requirements, flow rates, and supply temps, it's hard to say what is required to make it work, if it can. You may not have enough length, or the pipes are too far apart, or your supply temp isn't sufficient (and there are limits for the type of floor you can apply), or your volume isn't enough (there are limits on that as well for higher volume isn't linear in releasing more heat and then you can't push too much or you have problems with noise or erosion).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    In the trades Dana's Avatar
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    What type of tubing (PEX?, EPDM/Onix?), and what type of heat-transfer plates (if any) are you using?

    The fact that the water from the cooler zones is warmer than the more comfortable zones is an indication that you're not getting the heat out of the tubing and into the floor. If it's PEX and is either a staple-up or suspended tube with either no heat transfer plates or thin sheet metal plates, you can get a substantial performance boost out of going with the more expensive heavy extruded type plates. I'm not sure if this is ever done with Onix or other EPDM tubing (which tends to perform roughly equivalently to PEX in thin sheet-metal plates if installed to spec.)

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