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Heating and cooling: UFH Design for 1st floor on joists

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  1.  
    • CommentAuthortimmywo
    • CommentTimeDec 31st 2017 edited
     
    Hello all,

    After much research and thinking, I have come to the conclusion that I would like UFH on the 1st floor and do away with rads in our new build design (log cabin).
    For such a system I am not that keen on having no thermal mass (so not embedding pipes into insulation or using aluminum heat spreaders), so based on costs and practicality I have decided on the following DIY design...

    #Floor finish (hardwood / tiles)
    #20mm Screed 4/1 sand/cement with added fiberglass fibers
    #20mm EPS with pipe half inbeded
    #Vapour Barrier
    #18mm OSB Subfloor

    I think this will give me the best of all worlds, weight, thermal mass, pipe to screed contact, costs while not following best practices in any one area.

    I can see this is not ideal in many ways, but it appears the design of such things is based on one's needs and the above meets mine.

    Keen, as ever for feedback.

    Many thanks and an early Happy 2018 :surprised:
    • CommentAuthortony
    • CommentTimeDec 31st 2017
     
    Could you define first floor, is this upstairs?

    If new build how come you need heating upstairs?
    • CommentAuthortimmywo
    • CommentTimeDec 31st 2017
     
    Hey Tony,

    1st Floor as in upstairs - correct

    "If new build how come you need heating upstairs?" - the ground floor will have UFH, my location (south Poland) has +30 summers and -30 winters, I do not believe ground floor heating will suffice especially considering not all ground floors will have the heating on / high (utility room, guest room) - to be honest I have yet to do space heating requirements
    • CommentAuthorgyrogear
    • CommentTimeDec 31st 2017
     
    Posted By: timmywonot all ground floors will have the heating on / high (utility room, guest room) -


    What is meant by "not all ground floors" - do you mean "GF *areas* ?

    If so, why not go for a "simple" passive solar slab à la Riversong...

    https://riversonghousewright.wordpress.com/about/16-passive-solar-radiant-slab/

    gg
  5.  
    Posted By: timmywoHello all,

    After much research and thinking, I have come to the conclusion that I would like UFH on the 1st floor and do away with rads in our new build design (log cabin).
    For such a system I am not that keen on having no thermal mass (so not embedding pipes into insulation or using aluminum heat spreaders), but it appears the design of such things is based on one's needs and the above meets mine.
    Many thanks and an early Happy 2018http:///newforum/extensions/Vanillacons/smilies/standard/surprised.gif" alt=":surprised:" title=":surprised:" >


    So in the tradition of not answering the question asked.....

    Why are you convinced you need to create thermal mass upstairs - it adds quite a lot of complexity to the install. We got our UFH from http://www.wundafloorheating.co.uk/systems/ and fitted a mix of the thermal panel (under wood) and fermacell panel (under tiles. They seem to have replaced this with a chipboard system now).

    If you take the approach of running the heating constantly (we only switch off from 2200-0430) at a variable temperature using weather compensation I'm not sure the thermal mass is so important. It's a very thin screed you're proposing anyway.
    •  
      CommentAuthordjh
    • CommentTimeDec 31st 2017
     
    I'd be worried about the screed cracking, or is that thickness recommended by the maker/suppplier?

    It might be simpler to use a ready made screedboard?
    • CommentAuthorrevor
    • CommentTimeDec 31st 2017
     
    Upstairs I would not bother with screed unless it is a bathroom and you need to tile the floor. Why do you need a vapour barrier? Thermal mass here is not important and what you propose is miniscule in thermal mass terms.
  8.  
    ''I'd be worried about the screed cracking, or is that thickness recommended by the maker/suppplier?''

    If it really works at 20mm - and with 'half pipe embedded' that's 12.5mm in places - the fibres must be pretty wonderful! I'd expect lots of little bits of rubble after a while.
  9.  
    I went for rads upstairs in my retrofit, I wish I had just laid the pipes between joists now, the heatloss calcs I did for plastic pipes would have ensured it would be fine. But I'd rather someone else be the guinea pig as many people advised against this and said I needed a biscuit mix
    • CommentAuthorBeau
    • CommentTimeJan 2nd 2018
     
    We fitted UFH upstairs between the joists. Used what I think is know as a pug which is a very weak sand cement mix which is almost dry. It was supported on 25mm PU insulation which was sitting on side bearers and occasional cross bearers. Conventional floor boards covering. No problems with it and it does add some thermal mass which which suits our GSHP.
    • CommentAuthorGreenfish
    • CommentTimeJan 2nd 2018
     
    We have UFH in our single large upstairs/attic room as "insurance" and use it infrequently depending on the weather and how the room is being used. It could almost cope without heating at all, but despite good insulation the odd shape of the house (blame the planners) means we are not passive and MVHR moving air does not transport enough heat. Maybe some kind of incidental electric heating (fans heaters?) would have been more economical so far, but the UFH is the long term winner especially if room use increases.

    Much like Beau the UFH is between the joists, supported on 25mm PU insulation in a biscuit mix (went in as a fairly dry sand cement mix). Wanted to lay the T & G floor over it before the mixed had dried so laid a thin plastic sheet over first to avoid chipboard melt. Meant that it and the ceiling below had to try out downwards (like the other well sealed ceilings) but with the biscuit that ceiling did take a little longer. With just thin carpet tiles over it the UFH works without issue.

    Timmywo with your approach I would really worry about the thin screed cracking and not being suitable to lay a final hardwood or tiles finish. I know that the T & G acts as an insulant and slows down the heating response time compared to tiles on screed, and thus UFH needs higher feed temp, but that does work.
    • CommentAuthortimmywo
    • CommentTimeJan 2nd 2018 edited
     
    Hey eveyone, thank you all for your replies...


    Posted By: gyrogear
    What is meant by "not all ground floors" - do you mean "GF *areas* ?
    If so, why not go for a "simple" passive solar slab à la Riversong...

    Yes, areas \ rooms. While the main living space will have a large thermal mass heated somewhat via solar and UFH, I'm not convinced that upstairs would be heated via natural convection only (in my non-expert opinion)


    "it adds quite a lot of complexity to the install" - yes this is my main concern, along with trying to keep the mass around 2cm (weight/height reasons)

    "the need for thermal mass" - my main aim here is that I wish to benefit from heating the house with a low-temperature system, therefore I do not need to heat our Thermal Store so high. My concern with no thermal mass is that (from what I have read) I would need to run the pipes at a hotter temperature and would get patches of hot and cold on the floor.

    Simon Still - what temperature do you run your system at for upstairs?

    Posted By: djh
    It might be simpler to use a ready made screedboard?

    Yes, I am also looking at this as well, would be easier to install - sourcing this is the only challenge where I am. As soon as you look at something nonstandard here, sourcing costs rocket. Hence mixing my own screed would be easier to source parts for.


    Posted By: BeauWe fitted UFH upstairs between the joists. Used what I think is know as a pug which is a very weak sand cement mix which is almost dry. It was supported on 25mm PU insulation which was sitting on side bearers and occasional cross bearers. Conventional floor boards covering. No problems with it and it does add some thermal mass which which suits our GSHP.

    This is very interesting how thick is your "pug" mix? Im assuming the 25mm PU insulation holds the weight fine?
    • CommentAuthorBeau
    • CommentTimeJan 2nd 2018 edited
     

    This is very interesting how thick is your "pug" mix? Im assuming the 25mm PU insulation holds the weight fine?


    The pug is about 25mm thick if I remember rightly.Yes the insulation board copes with the weight fine but the joist are only at 400mm centres
  14.  
    Posted By: timmywo
    Simon Still - what temperature do you run your system at for upstairs?


    It's on a curve so depends on outside temperature. Currently 7.5C external and the flow temperature at the boiler is 28C

    32C at 0C external, 47C at -20 (though of course untested much below freezing here in London)
    • CommentAuthorgyrogear
    • CommentTimeJan 2nd 2018
     
    Posted By: timmywoI'm not convinced that upstairs would be heated via natural convection only (in my non-expert opinion)


    Perhaps not, unless you leave a floor opening at southern side...

    cf. "Zero Energy Design" video...
    https://www.youtube.com/watch?v=lzGaLw__kdk

    gg
    • CommentAuthortimmywo
    • CommentTimeJan 3rd 2018
     
    Hello all,

    Interacting video gg, lots to think about there regarding building design. While I love the idea suggested, due to limitations of the plot I have and the fact my project is classed as a "renovation", building design is limited. But still, lots of great info to think about.

    Posted By: Beau
    The pug is about 25mm thick if I remember rightly.Yes the insulation board copes with the weight fine but the joist are only at 400mm centres

    I need to check our design, I think our joists are at 500mm centres.

    I think the next logical step for me is to calculate the space heating requirements and look into Pug mix between joists or costs of sourcing ready made boards.

    I do like the idea of a dry Pug mix, as I would not need to worry about this cracking and it would assist with the diffusion of heat. Another chat regarding this: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2558

    Beau - do you remember if any moisture barrier was added to protect the joists? I am assuming the mix is very dry but there will be some moisture in there.
    • CommentAuthorBeau
    • CommentTimeJan 3rd 2018 edited
     


    Beau - do you remember if any moisture barrier was added to protect the joists? I am assuming the mix is very dry but there will be some moisture in there.


    No I did not add a moisture barrier. Once it's dry no more moisture to affect the beams. Should add it's not easy mixing a pug as it tends to turn into little balls and not break up nicely. I probably added too much water to get it to mix but it works fine. Since then I have been told use a large diameter mixer it mixes a dry mix much better.
    • CommentAuthorTimSmall
    • CommentTimeJan 5th 2018
     
    I have a thin screed over OSB (sealed with PVA) on upper floor bathrooms. Sand/cement screed with polyester fibres, and super plasticiser (reduce shrinkage and so screed cracking, and maximise thermal conductivity of the screed). 15mm UFH pipe installed at 100mm centres (where possible, slightly larger elsewhere).
  19.  
    Hi Tim, how thin is thin in your case?
    • CommentAuthorcjard
    • CommentTimeJan 6th 2018 edited
     
    I've aluminium heat spreader plates under 22mm chipboard, with 2.2 togs worth of carpet and underlay on top. The bedrooms are typically 2 degrees cooler than downstairs, and I can't imagine the downstairs heat makes an appreciable different because there's 300mm of acoustic wool under the spreader plates. It also doesn't help that an open plan top floor mezzanine above the bedrooms, with 25sqm of roof glazing provides some effective cooling

    All in, I like the bedrooms being cooler, though I do sometimes use a fan heater to zap the temperature of a room up e.g. For guests or when the kids are ill

    I've never measured the flow/return temps of the ufh to see how much heat is actually dispersed from the pipes, but it might be an interesting thing to to if I can find the infrared themometer as the heating has just come on- the sole house thermostat is downstairs and set for 17.1 during the day and 16.8 at night so it tends to go off at night and the bedrooms cool by a few fractions of degrees. One room has artificial grass instead of carpet and that's a much worse insulator, it hovers between 17 and 18 when the downstairs is 19-20 (the thermostat at 17.1 is 2 degrees off and I've never used it's calibration feature to make it accurate, I just adjusted all the set temps to be 2degrees lower, though psychologically this causes her to feel cold). Another room with full carpet is generally 16 to 18 and a third room where only half the floor is heated sees 15 to 18. The spreader plates route probably is working to some degree, but I'd apparently get much better results if I turned up the supply temp and I've also had comment that pug screed would give better heat spread/contact... I might also get better results if I actually used these fancy neo stat thermostats in every room, to control the manifolds, rather than just serve as expensive temperature data loggers.. the house does well enough on the sole thermostat (inside the controller for the ASHP) that I haven't yet bothered to fit any actuators, or even control the UFH pumps - they just run constantly, manually activated

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