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Thread: Retrofit underfloor radiant heating?

  1. #1
    DIY Junior Member LarryG's Avatar
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    Default Retrofit underfloor radiant heating?

    I am in the middle of 2 bathroom remodels. One has already had the wet-bed and tile installed on the floor. Is there a way to safely and efficiently install underfloor radiant heating? The rooms are on the second floor and the ceiling below have been removed to expose the underside of the subfloor. The subfloor is 1x4 tongue and groove. There is about 1 1/2" to 2" of wet-bed and pebble tile. My concerns; will heat radiate up through the wood subfloor, and will the heat damage the floor joists or subfloor? If this can work any suggestions for manufacturers or brands?

    I do not have hot water heat in the house and would hope to use an "electric tape" type heat source.
    Last edited by LarryG; 12-12-2009 at 02:18 PM. Reason: addition/clarification

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Hindsite is expensive! Do you have a boiler? You have a lot of mass to heat up. Electric would have worked in the floor sandwich (i.e., under the tile), but I don't think anyone would recommend it as a staple up. Hydronic staple up would work, but your supply temperature will need to be much higher (and thus less efficient) plus, you'd need plate diffusers to spread the heat more evenly. Response rates will be very slow. Either would have been much more efficient and easier to install as part of the mud bed underneath the tile.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default heat

    Wood is a very poor heat transfer medium, so you need a lot of temperature to penetrate it, then you also have to heat the subfloor and tile. Most electric panels have a very small BTU factor so they would probably have to work almost 24/7 to keep the floor warm.

  4. #4
    Licensed Electrical Contractor Speedy Petey's Avatar
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    I have NEVER seen an electric system to work this way, only water.
    Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.

  5. #5
    Extreme DIY Homeowner Scuba_Dave's Avatar
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    They do make them, I looked into them for our kitchen
    Basically they come in rolls that fit between the joists
    You'd need to most likely push rigid insulation up under them to trap the heat & heat the floors & not the air
    I never looked into it too much, decided against it as the kitchen has a large radiator

    http://www.suntouch.com/underfloor/

    After connecting your SunStat thermostat and testing the system, install R-11 to R-19 fiberglass batt insulation up to the mats. Also install insulation vertically at the ends of the joist bays or 6 inches after the mat ends.
    DIY Handyman (not 4 hire)
    I have enough to do to my own house

  6. #6

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    Don't waste your money, time or effort on an electric system in this particular case. You need a hydronic system.
    http://www.inspectpa.com/forum/forum.php
    My answers are based mostly on the ICC codes. Advice given is my personal opinion and every person performing work should acquire a permit from his/her jurisdiction and get the work inspected. My opinions are not directions to follow for DIYs or professionals

  7. #7
    DIY Junior Member mulveykemster's Avatar
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    Default Retrofit underfloor radiant heating?

    LarryG

    The newly constructed houses are now coming with the new Underfloor heating system. Underfloor heating systems require a wooden or tiled flooring to be effective and to work efficiently. The feel of suntouch com with underfloor heating makes you feel better. Hope you need this..

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