Unvented Cylinder Discharge

Discussion in 'Plumbers' Talk' started by Darkred05, Aug 24, 2020.

  1. Darkred05

    Darkred05 New Member

    Hello, I've got plumbers in to quote for installation of an upgraded electric hot water system. I have very low hot water pressure and the system is probably 20+ years old. It's an economy 7 immersion heater system.
    I've been told by one plumber I can get an unvented cylinder installed, with the tundish running into a plastic soil stack.
    I've been told by another plumber that an unvented cannot discharge into a plastic soil stack and therefore I need a thermal store to upgrade my system and increase the hot water pressure.

    I cannot discharge outside as this is a flat roof and I cannot get gas installed.

    Any help? I want to get this sorted but don't know where to turn and I don't have an quotes back for a thermal store so no idea of installation cost.
  2. Mike83

    Mike83 Screwfix Select

    A thermal store and unvented will both rely on decent mains pressure to achieve what it’s designed to do.
    These days unvented can drain into a plastic soil stack if pipework is suitable and fitted correctly.
    Would probably lean towards unvented over thermal if minimum pressure or flow can be achieved.
    What is you current mains pressure and flow rate?
  3. Darkred05

    Darkred05 New Member

    I believe my mains pressure to be good (runs my electric shower well) and doing a quick calculation with a jug of water gives me about 13litres per minute
  4. Mike83

    Mike83 Screwfix Select

    13 lpm ain’t the worst but you want 20.
    What’s your current flow rate from a hot tap. Check the bath and kitchen sink.
  5. Darkred05

    Darkred05 New Member

    The 13l was from my kitchen.
    Kitchen hot water... 6seconds filled 300ml so 3litres.

    Cold tap comes in at 15l
    Hot tap 8l
  6. Darkred05

    Darkred05 New Member

    My kitchen tap is a mixer tap, my bath taps are separate. It's 15mm piperpipe from water meter, inside my flat, to the cold taps.
    My electric shower does not struggle at all and that's a Triton ivory 4

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