Underfloor Heating

Discussion in 'Plumbing and Central Heating' started by wjrc, 11 Feb 2009.

  1. wjrc

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    Hi, I have a couple question regarding the preparation of the sub-floor for underfloor heating, I hope someone can help me.

    I will be having UFH installed in my kitchen, it is a suspended timber floor, the finished surface is to be tiled.

    I intend to prepare the floor myself, the plan being to remove the existing floor boards (to reduce the final overall build-up) and screw 18mm ply directly to the joists, with a further 10mm on top, running in the other direction, staggering joints as suggested by the BS.

    1)
    Will this provide a stiff enough base (considering I have removed the original floor boards) for my tiling? Or do I need a thicker ply build-up?

    2)
    What build up is required above the ply, ie screed or insulation mats?

    I expect the answer my depend on whether I am having electric or hot water - Ideally I would like hot water as I have heard it is a 'more even heat' any advice on this and how it would effect the base required would also be much appreciated.

    Thanks in advance for your help.
     
  2. John506

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    Whilst I can only help you with your first question.

    I would screw all the existing floorboards down as much as you can (watching you dont hit pipes or wires) and lay the ply ontop of that, countersinking screws along the joists, then between the screws in the joist, another load of screws into the floorboards.

    First though I would check all pipework under the floorboards is all strong soldered joints as removing the floor for leaks etc will be a PAIN!

    Try and make the gap between each screw 6inches north, south, east & west, to ensure the board is nice and tight

    When we have done this for bathroom floors which are also being tiled, the boss has gone and bought a big saver tub of 1000 2inch screws and we do use a hell of alot just to be sure.

    We have never put down a second layer and the tiles have all been fine, as long as it is solid then you are good to go.

    And between joints in the ply, screw screws either side every 2 inches.
     
  3. swidders

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    You need to decide now if it's wet or electric since wet goes under with insulation and screed between joists etc, whereas electric doesn't and can go within adhesive used for floor tiles

    T&G flooring sheets will be more solid and enable you not to have to have joints on joists
    depends on joist spacings but sounds like overkill
    Exactly - screed will go on insulation (kingspan or cellotex) between joists if wet system
     
  4. MadAlicesDad

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    Can't comment on how to tile on board, but from my experience, don't expect UFH to heat the room significantly! I suspect if it were left running all day it would warm the room slightly, but if you're running it off the radiator timer, then you may find you need a second heat source in the room.
    I've just fitted water UFH under a timber floor in the dining room. 75mm kingspan between joists, pipe clipped to kingspan, 22mm chipboard panels and laminate floor on top. Be aware that chipboard is a very good insulator! Don't know about ply.
    It does heat the floor so your feet don't get cold, but it is certainly not a replacement for a radiator.

    Mike
     
  5. Dan_Robinson

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    My living room is nice and toasty thanks...

    Your flooring might be too thick though. You will be getting 70W/m. But you don't need as much oomph as you would with a rad.



    Try Uponor System12...

    Otherwise it all depends on your pipe spacings...
     
  6. MadAlicesDad

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    Lucky you! Glad your experience is better than mine.
    I suspect that the boards are thicker than necessary, but as the main aim was to replace the springy rotten Victorian timbers, strength was more important than conductivity!
    At the weekend when it's on full time it's a lot better, but during the week when it's only a couple of hours morning and evening, you barely notice it other than as a foot warmer. That said, even with thinner boards and tighter pipe spacing etc, I still don't see how UFH mounted under* the floorboards can heat the air in a room as quickly as a normal convector radiator when used as an alternative to a radiator for only an hour or two at a time.

    * Uponor System12 mounts above the floor boards!

    Mike
     
  7. Dan_Robinson

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    I know - I have fitted System12...

    My underfloor is on a suspended timer floor with 18mm floorboards, aluminium spreaders and 75mm Kingspan.

    You can't expect it to heat the room with only a few hours morning and evening. Underfloor works at low levels for a long time. Mine is on an independent zone with a CM67NG.
     
  8. MadAlicesDad

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    I know that now, I just wanted to warn the OP!
    Mike
     
  9. wjrc

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    Thanks for the replies but I'm still a bit confused.

    Is a typical build-up:
    insulation between the joists, then board on top, then UFH (wet), then screed, then tiles

    MadAlicesDad, does this mean the pipes clip directly onto the insulation between the joists with the chipboard on top? Wouldn't it be bad to have the chipboard - a good insulator between the heat source and the floor?

    I think i need to do some more research on the basics - any pointers

    Thanks for the help
     
  10. swidders

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    Insulation between joist, set 25mm below top level of joist, UFH clipped to this passing through notches, light sand and cement screed (1 to 8 cement/sand) to act as heat spread, then boards on top.

    Research this.
     
  11. MadAlicesDad

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    No. in our case it was insulation, screed, boards, laminate
    Yes and yes. The latter point seems to have been overlooked by the sellers of UFH though!
    However, although it's not as good as I'd hoped, I'm glad it's there as it keeps your feet warm on an otherwise cold floor.
    Mike
     
  12. njk

    njk

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    Hi,

    Have a look at this
    http://www.uponorhousingsolutions.c...m & 16mm Install Guide - Domestic Systems.pdf

    We have used this system for about 8 years and it works brilliantly.
    The system 12 from Uponor is very good, only drawback is it considerably more expensive.

    In regards to controls, I always treat UFH as a separate zone, i.e. it's own room stats, programmer and zone valve. As previously stated, it should stay on for much longer and on a lower heat.

    Tiling wise, we use 18mm ply, screwed in at every 200mm, ditra mat http://www.schluter.co.uk/matting.aspx ) on top and then tiles.

    The only ufh I have come across that didn't work properly is either the house not being properly insulated and the heatloss being to great or the installation not being correct.

    Lolli
     

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