1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Underfloor heating

Discussion in 'Plumbing and Central Heating' started by deuce22, 28 Aug 2010.

  1. Bon

    Bon

    Joined:
    4 Jan 2007
    Messages:
    392
    Thanks Received:
    11
    Location:
    Lancashire
    Country:
    United Kingdom
    You'll struggle to get an output of more than 100W/m2 to be honest, and even that would need you to screed over your pipework to create a more even distribution.

    You also need a manifold as underfloor heating works at much cooler temperatures to a traditional radiator system (you don't want water circulating at 80-ish degrees where your bare tootsies are likely to touch) therefore a temperature mixing manifold is required to cool the primary flow temperature to your underfloor pipework.

    The other thing to consider is how well insulated your room is. In my (entirely commercial) experience u/floor is only used on its own in new builds with extremely well insulated rooms. In existing installations, you'd only use it to take the chill off a wood or tiled floor.
     
  2. Sponsored Links
  3. looneyfitter

    looneyfitter

    Joined:
    29 Aug 2010
    Messages:
    552
    Thanks Received:
    51
    Location:
    Merseyside
    Country:
    United Kingdom
    A circuit is a run of pipe. With ufh if you imagine the future down the pipe you get, the colder the pipe becomes so you therefore have to runmultiple pipes and split the load creating circuits.

    You will definitely req a manifold to bunch the circuits at the primary flow and return circuit from the boiler. You can pick a 7 zone manifold up for about £380 that includes the pump, manifold, blender and actuators. The problem with the way you plumber is describing is that you won't get enough flow to give the required heat output. For 60m I would split it between 6 circuits of 15mm poly pipe at 150 centres.
     
  4. Agile

    Agile

    Joined:
    26 Jun 2004
    Messages:
    64,017
    Thanks Received:
    4,591
    Location:
    London
    Country:
    United Kingdom
    Your heat calc seems wrong and you will not get that from UFH.

    You dont seem to be aware of the drawbacks of UFH.

    Its normal to add at least 50mm of Kingspan type insulation under UFH. That adds about 100mm to the floor height.

    Proper UFH has its own temperature mixing valve and pump.

    If you dont want to do it properly then its better to stick to rads or skirting heating.

    Tony
     
  5. looneyfitter

    looneyfitter

    Joined:
    29 Aug 2010
    Messages:
    552
    Thanks Received:
    51
    Location:
    Merseyside
    Country:
    United Kingdom
    How old is this house? Do you have any ideas what the sub floor is built up of? Anything upto 15-20 years old should already have 100mm of slab insulation fitted.
     
  6. deuce22

    deuce22

    Joined:
    7 Aug 2010
    Messages:
    385
    Thanks Received:
    1
    Location:
    Cardiff
    Country:
    United Kingdom
    Thanks Bon.

    I now realise what the manifold is for.

    So the way that this person has done it using a radiator valve will have the water temperature at the same heat as radiators, therefore making the floor ridiculously hot.

    I have re-furbished the front of the house where this flooring would be going.

    The internal walls have been taken down and I have renewed the insulation. The only problem I can see is due to the height of the ceilings.

    What I don't want to be doing is going through this expense and time for it to not heat the room up enough.
     
  7. Agile

    Agile

    Joined:
    26 Jun 2004
    Messages:
    64,017
    Thanks Received:
    4,591
    Location:
    London
    Country:
    United Kingdom
    You seem very sure your calcs are correct. I doubt it.

    100w/m2 is usually enough in normal houses.

    Tony
     
  8. deuce22

    deuce22

    Joined:
    7 Aug 2010
    Messages:
    385
    Thanks Received:
    1
    Location:
    Cardiff
    Country:
    United Kingdom
    Hi Agile.

    I used this site http://www.theradiatorcompany.co.uk/heatoutput/.

    I have put in the following info.

    Living room
    double glazed
    average
    The open plan is in the shape of an L, but the floor area is around 60m2.

    I have put 9m long x 7m wide.

    The ceiling height is 2.4 at the lowest up to almost 4m at the ridge. As an average I've put 3.25 into the calculator.

    It gives me a range from 28000 to 34000.
     
  9. Bon

    Bon

    Joined:
    4 Jan 2007
    Messages:
    392
    Thanks Received:
    11
    Location:
    Lancashire
    Country:
    United Kingdom
    I'd agree with Tony.

    Looking at my BSRIA "rule of thumb" book, a domestic dwelling needs a heat loads of approx 60W/m2. In my experience the BSRIA guide is usually well above what you actually need too (good for estimating though as I'm usually quids in when actually do the job ;) ) .

    In theory, your mate's system will work, in that it will circulate hot water under your floor. HOWEVER, whether it will overcome the heat loss in your kitchen/lounge/dining is another matter.
     
  10. Sponsored Links
  11. deuce22

    deuce22

    Joined:
    7 Aug 2010
    Messages:
    385
    Thanks Received:
    1
    Location:
    Cardiff
    Country:
    United Kingdom
    Hi Bon.

    I don't know what more I can do to reduce heat loss.

    I've fitted 150mm cavity insulation in the walls, 100mm between rafters with 40mm on the face.

    The placing of the radiators is going to be 1 under each bay that will give 4000 BTU's each, 1 on opposite sides of the room 9m apart that will give 9000 BTU's each and one roughly in the centre giving another 9000BTU's.

    I'm just thinking that less heat coming from all over the floor area will make it feel warmer than the radiator setup.
     
  12. looneyfitter

    looneyfitter

    Joined:
    29 Aug 2010
    Messages:
    552
    Thanks Received:
    51
    Location:
    Merseyside
    Country:
    United Kingdom
    Used my method all over my house with no problems at all. We also have a 30m2 all glass conservatory running off 3 circuits at 40 degrees which is nice and cosy. To up your w/m2 output you can always up your floor temp slightly to 40-45deg. If you have insulated as much as you've said then I feel you will be fine. We installed a massive under floor heating system in a car showroom at Christmas which had very very high ceilings.

    What do you plan in covering the floor with? A tiled floor will also feel alot warmer than a timber floor.
     
  13. mointainwalker

    mointainwalker

    Joined:
    24 Aug 2009
    Messages:
    2,461
    Thanks Received:
    240
    Country:
    France
    I think that most people would say that going from 30 C to 40/45 C is somewhat more than a slight increase.

    I'm also puzzled about your output of 100W/m2 at 150 mm centres. I believed that manufacturers say that is what you get with 100 mm centres and 30 C floor surface temp.
     
  14. DeltaT

    DeltaT

    Joined:
    7 Feb 2010
    Messages:
    689
    Thanks Received:
    50
    Location:
    Glasgow
    Country:
    United Kingdom
    Regs say floor surface temperature should be no more than 29*C. However, you can have a higher floor surface temperature around the perimeter or any area that you will not be walking on, this is common practice.
     
  15. looneyfitter

    looneyfitter

    Joined:
    29 Aug 2010
    Messages:
    552
    Thanks Received:
    51
    Location:
    Merseyside
    Country:
    United Kingdom
    Where have I once said that 150 centres will give 100w/m2.

    A typical ufh system will run between 35 & 50ish degrees. The System at my house runs at 40ish downstairs and 35 upstairs!!!!!

    Iirc concrete must run no higher than 55-60 to prevent cracking. Running at late 40-50 I'd still cheaper than running rads at 80-85 on a correctly setup system!
     
  16. deuce22

    deuce22

    Joined:
    7 Aug 2010
    Messages:
    385
    Thanks Received:
    1
    Location:
    Cardiff
    Country:
    United Kingdom
    Thanks guy's for all your advice.

    I have learned so much, just from this thread.

    I decided to go with U/F heating over radiators because I know the room will look much better without those bulky things all over the walls.

    However I do have a budget and I can't go over it that much.

    I now understand that it's the heat lost through the room, which is the main thing that I should be concerned with.

    What I don't understand is how the calculator can tell me to achieve 2.5 times what I will achieve, with 100w per m2.

    If I made sure that the whole area was insulated really efficiently, would have of what the calculator suggested be enough.

    I have a 1500w halogen fire and I cannot see that 6 of these would be enough to heat that area never mind just under 3.

    Is there a cheaper alternative to a manifold. Paying £300 just for that part would take the total cost over to much.

    Thanks.
     
  17. mointainwalker

    mointainwalker

    Joined:
    24 Aug 2009
    Messages:
    2,461
    Thanks Received:
    240
    Country:
    France
    @looneyfitter

    You are correct. I skimmed two posts and aggregated everything. Apologies

    Why though are you suggesting that someone have such a high surface temp, way beyond regulations ?
     
Loading...

Share This Page