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Community and Q&A

Underfloor hydronic: foil faced insulation or aluminum diffuser plates?

Trevor Laubenstein | Posted in Mechanicals on

Hello: I have a hydronic underfloor system (double pex-piping within floor joist space). The installer used NEITHER diffuser plates to hold the piping NOR reflective insulation. The performance has been disappointing and after having read many of your posts and Q&A I am convinced I should do one or the other at least. The insulation in the joist spaces is R11, kraft paper facing to the basement. I obviously only want to pull all this down and put it up once more, so my question is should I do the plates and put back insulation of a similar or different R value and/or switch the insulation to a foil-faced product, foil facing up toward the piping.

Thanks for any help you may have!

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  1. Jon R | | #1

    What aspect is disappointing? Efficiency, heat leakage to the basement, lack of heat upstairs? What is heating the water?

    You probably want to add plates and then reuse your same insulation.

  2. Trevor Laubenstein | | #2

    Basically all of the above, but primarily we are unhappy with lack of heat upstairs. When temps go below 25F outside, the radiant alone can never get the rooms to setpoint. System is fired with a new lochinvar condensing boiler using natural gas. Thanks so much for the response.

  3. Jon R | | #3

    Can you determine what the inlet/outlet temperatures are? It could be that you can get more heat out of the existing system. Plates will significantly increase output and somewhat increase efficiency. More insulation will reduce heat leakage into the basement (perhaps a non-issue).

  4. Expert Member
    Dana Dorsett | | #4

    Is this a staple-up (tubing in contact with the floor), or suspended tube (an inch or two between the tubing & floor)?

    What temperature is the Lochinvar output running when it's 25F outdoors? Unless it's running at it's maximum temperature and still not keeping up, you may be able to get there by simply re-programming the outdoor reset curve to something more appropriate. Or, if the water temperature is being mixed down in this zone, that could be tweaked. All modulating condensing boilers benefit from undergo some amount of curve optimization when first installed. If this wasn't done, it's not too late.

    Which model Lochinvar?

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