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  1.  
    An idle thought: does anyone use over-ceiling heating? Like underfloor heating, but from above?

    Problem: would like underfloor heating, but don't want to break out existing floors, and would like to retain newish carpets. No access under the floor.

    Idea: lift the wool insulation in the loft, lay ufh pipes and spreader plates between ceiling joists, replace wool. This will heat the ceiling to say 35deg. Conductivity of about 4W/m2k though ceiling plasterboard and surface, would give off heat into the room of 60W/m2 which is plenty. The warmth would radiate down onto the occupants, maybe would need forced ventilation to de stratify the air


    Any obvious flaws with this idea? Why does nobody do it?

    Also thought about radiant wall heating but put off by the disruption to replaster everywhere, and risk of picture nails.
    • CommentAuthortony
    • CommentTimeDec 10th 2017
     
    Maximises heat losses, minimises comfort, maximises heating costs
  2.  
    Why's that Tony? The ceiling is much better insulated than the floor.
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 11th 2017
     
    Partly because you are relying on the thermal conductivity of air (0.024 W/m.K) allow the increase in temperature at the heat source to permute down to the floor. This usually means that the emitter (the radiator) needs to be at a higher temperature than a low level mounted emitter. Convection currents are also hampered when the the top layer of air is hotter than the low level of air.
    There may possibly be some radiative energy to be had, but that would need a large dark emitter to cover the whole room just to heat a person. And the temperature would need to be high. This has been discussed to death and opinion is divided, so not going into the reasons.

    I am surprised that Tony is dismissing this idea as he has often said that a 60W light bulb can heat his house. :wink:
  3.  
    Many years ago I bought a house where the bathroom was fitted with a light which had an element around it. The result was the top of my head was hot and my feet were cold and the room didn't warm up much.
    • CommentAuthorowlman
    • CommentTimeDec 11th 2017
     
    Given your décor restrictions had you thought about Air/Air ASHP. Either the usual wall/ceiling emitters, low level wall emitters, or if you have the loft space ceiling cassettes.
    • CommentAuthormarktime
    • CommentTimeDec 11th 2017
     
    I think you'll find that the optimum physiological heating profile is feet warmer than head, e.g. UFH or blown air at skirting level. Earlier comments also apply.
    • CommentAuthordelprado
    • CommentTimeDec 11th 2017
     
    This is quite common in Germany, apparently, especially in commercial settings. I am not certain of the exact benefit of it. I looked at wall heating, because it opens up more possibilities for floor coverings, which are otherwise limited by UFH
  4.  
    Potentially useful under the upstairs floors in an upside-down house?
    • CommentAuthorFred56
    • CommentTimeDec 11th 2017
     
    The bungalow I own and live in was built inthe 1970s. It's on an estate of about 100 prooerties. The type that I have were all built with ceiling heating. More interesting is that they were all built in cavity block but with internal wall insulation. The ceiling heating was a 100% unmitigated disaster. It was electric, there is no mains gas round here. Everyone go rid of it very quickly. Most went for night storage heaters some for oil and some for lpg.

    The system was called Riviera radiant panels and was made in Penryn. Consisted on 3/4 inch polystyrene boonded to a fire wire a bit like the screen heaters in a car. The whole then wrapped in plastic. They were about 2ft square. Each had tails and these were connected (this will amaze electricians) by those nasty scotch locks they used to bodge tow bar electrics back in the day. Most of the ceiling was covered between the ceiling ties. The remaining area had regular 3/4inch polystyrene. Over that there was a layer of very coarse glass wool about and inch thick. Brilliant. Hot air doing its stuff in a ventilated roof space.

    We've learned a bit since then so we may be able to make it work now.

    Next time I am in the loft I'll rip out an old panel and post a photo. If I can find one of the fried ones you can shudder at the fire risk. Quite a few had obviously gone into meltdown.
    • CommentAuthortychwarel
    • CommentTimeDec 11th 2017
     
    I did think about doing precisely this arrangement but to cool a plant room, think it would work but never got round to it.
  5.  
    Thanks all!, just to be clear I'm not thinking of a small hot electric panel - I'm looking at low temperature central heating water ufh pipe evenly heating the whole area of the ceiling, and covered by two layers of 200mm wool. The CH is heated by our existing ashp.

    I'm looking at getting the ceiling surface 10deg warmer than the room temp, which gives radiant heating of εσ(T^4-t^4) = 60W /m2. Any convection heating on top of this would be a bonus but not really needed.
    • CommentAuthortony
    • CommentTimeDec 11th 2017
     
    And massive losses through the insulation with Delta T an extra 10 degrees, I would think a lot of additional insulation would be needed
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 12th 2017 edited
     
    Here is a calculator:
    https://www.engineeringtoolbox.com/radiation-heat-transfer-d_431.html

    Put in 0.9 for emissivity
    303 K (10 K above ambient)
    293 K (ambient 20°C)
    1 for area
    Get out 380W

    Even dropping the emissivity to 0.5 still gets you 211 W/m^2

    At 0.9 emissivity and an emitter temperature of 293.4 will give you 14.8W/m^2

    Do you really think this is right?
  6.  
    ST, that doesn't look right

    0.9×5.67E-8×(303^(4)-293^(4))
    =54.0326909304
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 12th 2017 edited
     
    I just used the online calculator.
    Just did this is Excel and got this:
      radiation.jpg
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 12th 2017
     
    Whoops, seen my error. Put in an ^ instead of an E
    Yes for the 54, but different from the engineering toolbox calculator.
    No idea why.
    •  
      CommentAuthordjh
    • CommentTimeDec 12th 2017
     
    Posted By: SteamyTeaYes for the 54, but different from the engineering toolbox calculator.
    No idea why.

    Because it clearly says temperatures should be in °C not K?? :devil:
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 12th 2017
     
    Ah
    That will be why. I had had a busy night and was a bit groggy this morning.
  7.  
    Posted By: tonyAnd massive losses through the insulation with Delta T an extra 10 degrees, I would think a lot of additional insulation would be needed


    Good thought, an extra 10deg through an U=0.1 ceiling gives additional 1W /m2 loss. Normally the heating won't be on full whack, let's say it is for 2000h/year. So extra annual losses 1W/m2 x 2000 h = 2kWh / m2, costs £0.12/m2/year. That isn't going to pay for any more insulation, but no harm adding some while working in the area.
    • CommentAuthortony
    • CommentTimeDec 12th 2017
     
    How long will the house be there being heated? 50 yrs? = pays for a lot of insulation even 25 yrs and without inflation
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