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Radiant heat insulation between conditioned floors

W N | Posted in General Questions on

Hi, I read your article questioning the need for radiant heat on a second floor. My question/concern relates to this but is particular to my situation.

I have installed radiant floor heat (not yet charged or insulated) in the first and second floor (separate zones) of my old farmhouse. I have all new low e windows and will be using spraying poly on the walls. The house will be tight! My contractor thought I may never use my second upstairs zone particularly, since I’ve also plumbed in a wood stove on the first floor. The bottom floor is 800 sf and the second is only 400 s.f.

My concern is that it may get too hot upstairs if the woodstove is on and how do I sound proof between floors? The “TV” room will be directly below the bedroom. How much or should I even insulate between floors. I thought of using rock wool for sound deadening yet limited R value to allow easy heat transfer between floors. Your suggestions/opinions will be of great help. Thanks


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  1. Richard McGrath | | #1

    If you'd like the radiant heat to actually work you will require insulation below the tubing . What type of tubing install is this ?

    Heat from a woodstove will travel upstairs , no need to attempt heat transfer through floors .

    I am curious as to what you mean when you say there is a woodstove plumbed, could you elaborate ?

  2. GBA Editor
    Martin Holladay | | #2

    Here is a link to a GBA article that discusses how you can reduce sound transmission: How to Keep the Noise Down. The article includes useful links in the "Related Articles" sidebar.

    Don't worry -- the wood stove heat will reach your second floor, even with insulation in your floor assembly.

  3. Andrew Bater | | #3

    Martin, I had surprisingly different experience with this.

    Our second floor bedroom is surrounded by SIPs on three walls and in the cathedral ceiling, and noise control insulation in the wall between it and the adjacent bathroom. It's a carpeted floor, with spray foam filled open web floor trusses underneath.

    I put a dedicated thermostat in that room thinking that the heat would almost never be needed; the heat from the 1st floor radiant system would make its way up there. Really didn't seem smart for the pump feeding the panel radiator in that (and adjacent) room to be idling all the time waiting for the thermostatic operator on the radiator proper to open.

    I was quite wrong, that room is the coldest room in the house, even when we are running the masonry heater central to the 1st floor. I had a friend from California here early last fall and he was freezing. I had to switch the geo system to heating mode much sooner than I would have imagined. The only explanation I can come up with is that due to the home's tight air-sealing (.9 ACH50 as last measured) there is no stack effect at all into that room, and it functions as a little icebox.

  4. GBA Editor
    Martin Holladay | | #4

    Thanks for sharing your experience. It just goes to show that every house is different, and the exact circumstances of the construction matter.

  5. W N | | #5

    Richard, I've plumbed (piped) for a wood stove but it has not yet been installed. The stove will likely be able to heat the entire home on its own with good circulation. We are planning on two ceiling fans downstairs and one up(which has an open floor plan) master bedroom. I have the onyx tubing installed w/o the radiant "fins". The second floor is full 1" pine T&g w/ no subfloor. I plan to use the wood heat to supplement (not primary) for those really cold nights, or fast drops in temp.

  6. D Dorsett | | #6

    Are you planning for a Hilkoil retrofit into a wood stove, or are you talking about installing a wood-fired hydronic boiler?

    BTW: The history of EPDM tubing in radiant heating has a very checkered history. They claim to have fixed most of the problem issues with Onix, but some skepticism is warranted.

    With open doors to a stairwell convection will move a LOT of heat from a first floor wood stove to a second floor. In my not-so-well insulated upper floor of my 1.5 story 1920s antique I have no problem heating the ~432' of upstairs space with the wood stove in the first floor living room through an open 32" doorway (even at sub-zero F outdoor temps), but some of the doored off first floor spaces will run considerably cooler even with the doors wide open. YMMV.

  7. Richard McGrath | | #7

    Dana said ,

    "BTW: The history of EPDM tubing in radiant heating has a very checkered history. They claim to have fixed most of the problem issues with Onix, but some skepticism is warranted."

    Dana is correct . EPDM tubing does not do well with high temperature fluids . Hopefully you have none to very little ferrous components in the Plumbing to the woodstove , ingress of oxygen will certainly make quick work of destroying any of those that exist .

    By your description , you have a suspended tubing system , not even staple up . This will require high temp fluid to achieve anything close to usable heat on the floor above .

    May I ask why you chose Onix and the suspended tube approach ? Was it based on first cost , recommendation , internet searches ?

    Please read the following if in fact it is not too late , address your install

    Good luck and if you have any questions I can help you with , feel free to ask .

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