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Unvented Cylinder, thickness of pipe, reduce water flow

Discussion in 'Plumbing and Central Heating' started by izrr, 31 Aug 2010.

  1. izrr

    izrr

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    Hello

    My plumber has recently installed a Worcester boiler and an Ariston unvented cylinder, 210ltr. I am also having a loft conversion.

    The pipe coming from my water meter on the pavement is the copper 15mm pipe. Inside my property on the ground floor under stairs cupboard; my plumber changed the pipe from 15mm to 22mm. This runs up above to my bathroom where my cylinder sits, the rest of the pipes are 15mm. From my bathroom, the 22mm runs straight up to just before the loft conversion. The cupboard where the cylinder rest is located beneath the top end of the stairs leading to the loft conversion. The 22mm pipes go up straight but my plumber changed them to 15mm pipe across beneath the top end of the stairs and into the shower room in the loft conversion. All the pipes are 15mm in the loft conversion.

    My water pressure is 3 bar in the garden. The pressure in the loft shower room in 2.5 bar but when the basin mixer is opened, the pressure reduces/drops.

    The flow of the water reduces in the loft when the water is opened in the first floor bathroom. I have been told that my flow of hot water is greater than my cold water.

    I was told that once the unvented cylinder goes in, I will be able to use the water/showers at the same time with no flow reduction of water.

    Now my plumber tells me that this problem is due to the fact that I have a 15mm copper pipe coming into the property and I need to change it to 28mm pipe, which is another expense.

    I would appreciate any help in this matter.

    My question is:

    Is it because my plumber did not carry the 22mm pipe into the loft shower room thats causing this problem?

    Is it true that I need to change the pipe in my driveway in order to get the flow?

    Is there something else we need to do to get the same flow of water everywhere?

    Thanks
     
  2. dreadnoughtheating

    dreadnoughtheating

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    With Unvented Cylinders (as with many things in life.... sigh ), you can really only expect to get out of them what you put in. This is especially true of water, take a look at getting an 'Accumulator' installed alongside the cylinder, this will 'boost' output, for a while until its airpocket is exhausted, or, rip out the Ariston and get Heatrae Megaflo in instead.
    Did your G3 ticket holding jnstaller - he has got G3 hasn't he?????? - check incoming dynamic pressure AND flow rate before he quoted a price?

    Has it been Benchmarked (tickbox/checklist supplied with vessel) and notified to your local building Control Office?

    Just a few questions that you may wish to raise with yourself AND the installer.

    DH
     
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  3. ajstoneservices

    ajstoneservices

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    You need to upgrade the incoming main to at least 25mm.
     
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  4. looneyfitter

    looneyfitter

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    upsi ing cold mains pipework with in the dwelling is not recommended as it will REDUCE pressure not increase it.

    You can only flow so much through a 15mm pipe. Pressure helps the flow along. I would have stuck to 15mm throughout or upgraded your incoming main to 25mm and ran 22mm from that.

    Definately not ran 15-22 this will only make things worse.
     
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  5. looneyfitter

    looneyfitter

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    Beat me to it :D
     
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  6. ajstoneservices

    ajstoneservices

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    makes a change ;)
     
  7. mysteryman

    mysteryman

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    There is a lot of tosh in these replies.

    Changing from one make of unvented cylinder to another will not improve things at all, and installing a length of larger bore pipe will not reduce the pressure.

    The basic problem is that your incoming supply pipe is not big enough in diameter, as several others have said. Without any cold water storage, your cold main is the driving force behind all your taps. This has to supply all the hot and cold draw offs at once, and the more you try to draw, the less the pressure will be. Bear in mind also that you lose 1 bar for every 10 metres you go up.
     
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  8. looneyfitter

    looneyfitter

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    Erm yes it will. so your saying that if you have a 1m length of 15mm connected to a 1m length of 22 and an open end at the 22mm you will have the same amount pressure as you would if it was the other way round?

    It wont reduce standing pressure but will reduce working pressure,

    Put your finger over the 22 slightly, does the pressure increase? YES

    Does the flow increase? NO

    Your getting mixed up with flow and pressure mate.
     
  9. mysteryman

    mysteryman

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    I am not. A finger over the end of a pipe is not an accurate way of checking pressure!
     
  10. looneyfitter

    looneyfitter

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    We both know that!!! I am merely trying give an idea of what i mean. Surely you have fitted a combi to a 22mm pipe and the water flow at the bath has been crap. Change it to 15 all is well.

    another way to look at it is if you fill a tank with water, is the water sitting in the tank the same pressure as the water coming out the feed? NO

    Its hard to explain here buy you lose WORKING pressure by up scaling pipework

    Whole heating systems are disigned on flow rates and pressure drop. Its all relative
     
  11. izrr

    izrr

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    Excuse me if I seem ignorant, just that as I am not in this trade, this is not making much sense to me.

    All in all, what I understand is that I need to change the main pipe to at least 25mm in order for it work, am I correct?

    Thanks
     
  12. ajstoneservices

    ajstoneservices

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    The 25mm will give you a better flow rate not higher pressure. The problem you have seems to be poor flow so bringing in a new main of at least 25mm will give you the improvement you want/need.
     
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  13. mysteryman

    mysteryman

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    Basically, yes.

    I believe that looneyfitter is trying to make the point that delivering hot water through smaller pipes reduces the dead capacity and wastage of heat from hot water pipes.

    Otherwise, a larger bore pipe will allow more water to flow through, especially in the cold water main.

    You need to filter out the tosh rom the truth in these posts.
     
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  14. ajstoneservices

    ajstoneservices

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    MM,
    That's not particularly helpful is it.
     
  15. mysteryman

    mysteryman

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    I think it is very important that the users of this site, the DIYers, are aware that they need to choose very carefully whom they believe.
     
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