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D2 pipework options for unvented cylinder in loft

Discussion in 'Plumbing and Central Heating' started by BadgerParty, 15 Jun 2021.

  1. BadgerParty

    BadgerParty

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    Hi,

    Apologies if this has been answered elsewhere, I had a search through but I couldn't find anything.

    I am installing a 200l direct unvented cylinder in my loft. I am running all the pipework up to the cylinder, and the the G3 certified plumber will be doing final connections and commissioning.

    Where I'm getting tied up in knots, is the D2 discharge pipework. The D1 discharge pipe is 15mm. The way I see it I have three options:

    1) 28mm copper pipe, through the wall directly under the eaves, and straight down the wall adjacent to the PVC guttering, terminating at ground level and basketed in. Total run length around 9m, with around 5 or 6 elbows, so that permits me something like 12m of run length. Does the vertical drop count towards run length?

    2) 28mm copper pipe along length of loft to opposite end, down through the wall, and couple onto a cast iron soil stack using a suitable boss. However, I can't seem to find a suitable adaptor for taking 28mm copper up to 32mm waste pipe size. If I'm going into the soil stack, I was planning on using a Hotun dry tundish, but I'm not sure it it can handle the flow rate (35l @5 bar, not sure what flow rate it would be when regulated down to 3 bar). Alternatively I'll use a 32mm HepCo waterless valve.

    3) Same as runs 1 or 2, but do everything in 32mm polypropylene. However, looking at the guidance, it says polypropylene shouldn't be used outside as the UV light can weaken it. Is there a UV stabilised polypropylene?

    Should I just wash my hands of it, and ask the plumber to spec and install the D2 pipe? I want it to comply with regulations, but the more I read into it the more complicated and restrictive it's getting.

    Thanks,

    Phil
     
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  3. ianmcd

    ianmcd

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    if inlet is 15mm, outlet only has to be 22mm, 28mm wont do any harm but doesnt need to be 28mm, you dont need to run it to ground level, just turn it back to the wall where it exits
     
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  4. BadgerParty

    BadgerParty

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    Thanks Ian,

    28mm was selected based on the expected run lengths, but if I can get away with 22mm then that's great.

    Looking at the guidance on discharge termination, I didn't realise that pointing it back towards the wall was an acceptable option. The only things I could find regarding discharge from high level was to either pipe it down the wall and either terminate 100mm above ground level with a basket or into a covered gully, or to boss it into a soil stack. If I'm allowed to do that, then it makes my life a lot easier.

    Cheers

    Phil
     
  5. Madrab

    Madrab

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    If you are following the legislation to the letter, under G3 requirements, any discharge termination point can not constitute a danger to anyone. If the proposed termination point is in a position where, if discharging, high pressure boiling water could be a danger to someone, then it's not allowed. Hence one of the requirements for it to terminate no more than 100mm above ground and be guarded.

    That being said, turned back to the wall happens all the time, especially if there is little danger of it spraying onto anyone below due to its location. My discharge is 5 ft away from my back door 2.5m up, therefore it could spray off the wall and scald someone below .... it's another thing on my list of stuff to do.
     
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  6. ianmcd

    ianmcd

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    if turned back to the wall and the PRV discharges, which is very unlikely, they do pass for fun but very rare that it will ever actually open full bore, the water will hit the wall and run down it, wont be a danger to anyone, regs say that the outlet from the tundish must be 1 pipe size larger than the inlet so 22mm is fine , as said highly unlikely it will ever be required but has to be there
     
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  7. BadgerParty

    BadgerParty

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    Thanks everyone,

    The discharge point is at the edge of my garden, near to the fence with my next door neighbour. there are no doors or windows directly underneath the discharge point.

    I think the new plan of attack is to run 28mm tubing out the wall at high level, and attach a couple of elbows or bends using compression fitting so it points back towards the wall. If the plumber or building control doesn't like it, then I can remove the elbows, and attach a run of pipe down the wall to ground level, and terminate in a basket. 28mm will give me the run length to allow this if I need to run to ground, whereas 22mm would not (after factoring in all the bends).

    Does that sound like a good approach?

    Thanks,

    Phil
     
  8. ianmcd

    ianmcd

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    yes it will be fine
     
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