hot water pipe size from Combi?

Discussion in 'Plumbers' Talk' started by house of horrors, Dec 4, 2006.

  1. house of horrors

    house of horrors New Member

    Hi

    Currently refurbishing two spare rooms and have both sets of floorboards up. I'd like to take this oppotunity to re-direct the hot water supply to the bathroom. This currently does several site seeing tours of the house before arriving at the bathroom, cold!

    I'd allways thought that this supply should be 22mm, dropping to 15mm at each appliance (except the bath) however the feed from the combi boiler is only 15mm. Is this due to the restricted hot water supply from a combi? and therefore all pipework after this point should be 15mm? Is there any point installing 22mm?

    Would like to put the pipework in now while I have the chance and do the final connections at both ends later.

    Any help would be really appreciated, thanks.
     
  2. Zorro

    Zorro New Member

    The only 22mm pipes coming from a combi are the the CH flow and CH return. Everything else is 15mm.
     
  3. house of horrors

    house of horrors New Member

    great, thanks Zorro, appreciate the reply.
     
  4. Garfield

    Garfield Member

    Except the gas which sould be 22m or 28mm depending on length of run etc etc
     
  5. Zorro

    Zorro New Member

    Yeah, sorry I meant pipes containing water.
     
  6. Garfield

    Garfield Member

    Just thought id mention it,as he says the HW is cold.Long runs of pipe dont help though.
     
  7. house of horrors

    house of horrors New Member

    thanks for the help.

    With a conventional boiler and system would this pipe be 22mm or would it always be 15mm? As it is a present, bit bodged by previous owners it goes from 15 - 22 and back to 15 again!

    Thanks
     
  8. devil's advocate

    devil's advocate New Member

    Hi hofh.

    The reason that combis have only a 15mm DHW feed is because the water is being delivered at mains water pressure (generally much higher than that delivered from a storage tank) and therefore doesn't require a larger pipe to reduce friction.

    Using 22mm will actually be a disadvantage in this situation as it simply means a greater amount of sitting water needing to be shifted before the hot water gets to you. 15mm pipe, only, will help!

    Obviously, try and keep the runs as short as possible. This might involve having separate runs to individual taps, if keeping the current system means that the pipework to some taps are significantly longer than they need to be 'cos it travels via a tap in a different corner of the house - if you see what I mean.
     
  9. house of horrors

    house of horrors New Member

    Hi DA

    Thanks for that, makes perfect sense now, of course. Judging by the length of runs in this house I think the electricians and plumbers must have been paid by the metre! ;)

    Forgot to ask though, and final question I promise. The cold feed is 22mm, is this correct or should this be 15mm as well? We're in the sticks a bit so are not on mains water so all water is pumped from a bore hole, through a filtration system, and around the house. All pump and filter pipework is 22mm. Again though it does drop to 15mm, for its grande tour, and pressure in the bathroom is fine, pressure is regulated by the pump though at a min of 3bar.

    We have tried to get people to sort the whole system out, but they just scratch their heads, 'go for parts' and we never see them again. I understand it a little more now as I've worked my way through the house and have seen each part of the system but it isn't easy.

    Thanks.
     
  10. devil's advocate

    devil's advocate New Member

    Hi hofh.

    By 'cold feed', do you mean the supply up to the boiler, or the cold supplies to each tap?

    If the former, then this is best left as it is - presumably, it was designed to suit the delivery of your pumped borehole system.

    If you mean the cold supplies to each tap, then it doesn't really make much difference (unlike with the hot where you want the standing cold water displaced as quickly as possible). So, no point changing it.

    A min 3 bar pressure is pretty good.
     
  11. house of horrors

    house of horrors New Member

    Yes sorry, I did mean the supply to the taps.

    Thanks DA
     
  12. If your mains pressure is good then 15 mm cold supply to the boiler is fine but if its a little poor then it can help a very little to feed the boiler with 22 mm.

    Tony
     
  13. house of horrors

    house of horrors New Member

    Thanks for everyones help, I'll be installing two 15mm pipes tomorrow before the boards go back down so very gratefull.
     

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