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Community and Q&A

Second story hydronic radiant floor system

user-963148 | Posted in GBA Pro Help on

We notice that the hydronic system for the 2nd story tends to warm the ceiling of the 1st floor rooms below rather than the floors as was intended. Our second story was built with hydronic loops between the floor trusses on the underside of the subfloor using thin metal (not aluminum) heat transfer plates. Laminate flooring and some tile in the bathroom cover the floors. I read and others suggested to blow insulation between the floors and insulate the ceiling cavity to force the heat upwards. Without tearing out the ceiling, how effective will a vermiculite or cellulose insulation be to force the heat up through the subfloor and what product(s) could you suggest? Has anyone had any first-hand experience and can share the results?

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  1. GBA Editor
    Martin Holladay | | #1

    I would think that cellulose would work well for this application, but I'm open to hearing from anyone with direct experience with this type of problem.

    -- Martin Holladay

  2. Expert Member
    Dana Dorsett | | #2

    For most houses R10 of fluff is plenty for zone isolation on radiant floors & ceilings. That's usually installed at the same time as the radiant heating. If there's nothing but air in the joist cavities a full-fill is overkill, but unless you're pulling the ceiling gypsum it's hard to know that you've completely covered it if you don't fill it all up. Low density cellulose is just fine for this.

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