Underfloor heating planning

Discussion in 'Plumbers' Talk' started by rmjo, Jul 11, 2019.

  1. rmjo

    rmjo New Member

    Hi all,

    I want to install underfloor heating in a fairly large room, using 3 loops. With the current pipe layout in the house (1870's), it would be most convenient to come off the pipes towards the end of the circuit. I plan to install Drayton Wiser TRVs on each radiator (reason for choosing Wiser, they were on sale so I went for it - so I do plan to use these, not another brand).

    I've not dealt with UFH heating before, so my question is, how do I control the temperature of the UFH area? All three loops are within one large room, so separate control over each loop is not needed.

    If I have to, I could run new pipes back to the boiler for the UFH heating, but I'd prefer not to. If it makes any difference, I can also move the pipes for the final radiator, but again, I don't know if that makes any difference. I've been reading about zone valves, but not sure where I'd locate them in this plan.

    I appreciate any help, I want to learn. I'm a competent DIYer, so the work doesn't phase me, as long as I can do it correctly.

    Thanks Central-Heating.png
  2. Dave Marques

    Dave Marques Member

    UFH should be on a separate zone.
  3. sospan

    sospan Well-Known Member

    Is that a single room you are putting UFH in ? with rads in a hallway / upstairs ?
  4. rmjo

    rmjo New Member

    Yes, it's a large 50sqm room, the rads are in 2 further downstairs rooms (utility and WC) and upstairs.

    Excuse my ignorance, but does putting the UFH on a separate zone mean running new pipes back before the first rad tees off?
  5. sospan

    sospan Well-Known Member

    Typically you would have a zone of one or two rooms so you can control the temperature.

    I am not an expert by any means but the layout i have seen for larger rooms have the pipe flows almost concetric so you don't get the cold zones there the returns are. So for your room may need the each feed line concentric as well

    The Teach likes this.
  6. andyscotland

    andyscotland Active Member

    Yes, ideally you'd need to tap off the boiler with a 3 port motorised valve before the radiators - UFH operates at lower temp than radiators and for longer/different cycles so you need to be able to have the boiler feeding just rads / just UFH / both.

    I suppose you might get away with it if all the rads have TRV's and you then put a TRV / thermostat controlled valve at the UFH manifold but it won't be as efficient and will be harder to balance.
  7. dobbie

    dobbie Well-Known Member

    You will need a 2 port valve for the radiator circuit and a 2 port valve next to the manifold/pump blending valve you will not need actuators as it is the one zone.

    You will have a wiring centre here also where everything can be connected and the floor controlled by a suitable room stat/programmable stat for underfloor heating.

    The diagram you have posted would not work as you would need a 2 port valve to all your radiator drops.
  8. rmjo

    rmjo New Member

    Thank you all for the replies.

    Can anyone explain why it wouldn't work to have just a single zone valve where the UFH tees off as in the attached image. If all the radiators are controlled by smart TRV's, do they need to be separated by their own zone valve? I understand they would if they were standard TRVs, or even if just one was a standard TRV, but if all are smart, why do they need separate zoning?

    Attached Files:

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