Unvented below sink water heater- PRV drain

Discussion in 'Plumbing and Central Heating' started by 4xpaws, 5 Aug 2007.

  1. 4xpaws

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    I'm having a 'below sink' unvented water heater installed in the loft. It needs a pressure relief valve installed in the pipework along with it. Has the drain coming from the PRV & tundish got to be copper? or can it be PE-X barrier pipe?
     
  2. Doctor Drivel

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    Avoid these. Fit a heat bank thermal store.
     
  3. 4xpaws

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    Thanks for comment.

    One reason amongst others is too long a pipe run is needed to fit thermal store. 30m+ run needed. Its for 3rd floor and storage cylinder's in basement.
     
  4. Dan_Robinson

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    What make and model?

    I think it would have to be copper.

    What are you feeding with it?

    Why not fit a secondary return - much lower running costs and less maintenance.
     
  5. 4xpaws

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    Speedlow SF10Li unvented water heater

    feed from mains.

    Secondary return -what's all that about? Returning to where?
     
  6. jay1

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    does it need to have prv and tundish if it is storing less than 15 litres, im pretty sure its doesnt need to.
     
  7. Doctor Drivel

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    A DHW secondary circulation pump can be fitted to a thermal store heat bank.
     
  8. 4xpaws

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    Comes supplied with PRV + all fitting senarios show the 6 bar PRV installed.
     
  9. Dan_Robinson

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    Its basically just a loop going back to the cylinder that re-circulates the hot water using a bronze pump set on a timer/timer & thermostat so that the hot water doesn't take three weeks to get to taps at the opposite end of the house. Hotels use it as do hospitals.


    You haven't answered the main quetion of what it's for.


    DD the man doesn't need a thermal store; leave it - for a change.
     
  10. Nige F

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    Fraid not, they come with a PRV and you have to allow 4 meters of supply 15mm pipe for expansion back up the supply pipe before a draw off on said supply.........or 2 metres of 22mm pipe ;) I would run copper and use a 22x35 reducer as a tundish.......in fact I`ve done 2 now ,as they are not covered by unvented certificating ;) which I aint got
     
  11. 4xpaws

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    Pipe run involved means its too costly in terms of labour & materials + access needed to install run is difficult. Forget it.

    The heater's bought and now needs fitting (correctly)!
     
  12. Dan_Robinson

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    You are welcome.

    :rolleyes:
     
  13. 4xpaws

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    Its to supply a sink in a 3rd floor bathroom. Boiler and cylinder a down in basement. Cold tank is on the 3rd floor too. Previous plumber said the under sink heater was the best option for getting hot water to 3rd floor sink.

    -The fitting instructions show at least 2.8m of 15mm pipe is needed for expansion to the nearest cold draw off from the heater. As the curent main supply is 15mm, adding reducers and a section of roughly 1.3m of 22mm between the nearest cold draw off and the 15mm fitting to the heater is acceptable??

    Fitting a length of 22mm -would this step up the the size pipework needed for the PRV discharge? Currently with the PRV Tee'd off 15mm supply, discharge pipe D1 (PRV to tundish) is 15mm & D2 (tundish to outside) is 22mm.

    With this 22mm 'expansion' section would D1 now become 22mm and D2 28mm??

    -Finally, can the PRV drain pipe discharge onto a roof, or has it got to go 3 story's down to a surface drain, or... can it vent into the cold water/ DHW cistern?

    I'm a bit bemused you can't use barrier pipe for the drain given that you can use it for other HW CH applications.
     
  14. Dan_Robinson

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    You want to use a 10 litre unvented heater to run a bathroom?

    hhhmmmm. Are you sure?

    I wouldn't terminate it over the roof unless you had at least three metres of surface before it entered the guttering.

    It would be a copper pipe as the PEX pipe might not handle the superheted water/steam that is released under fault conditions.

    Hence avoiding the termination of the Safety discharge over the roof.

    I don't think you quite understand how all this works do you?

    The size of the incoming main has little bearing on what happens after the heater with regards the safety discharge.
     
  15. Balenza

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    Dan Robinson wrote

    Sounds like he only wants to provide hot water to a basin. :!:
     

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