Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

Can someone explain to me the issue with 1/2 inch pipes

  • 12-04-2020 08:00PM
    #1
    FutureGuy
    Moderators, Computer Games Moderators Posts: 15,255 Mod ✭✭✭✭


    Hi there,
    Had someone look the central heating of a house we bought with the idea of replacing the gas boiler with a new model. Rads are about 5 years old but boiler is about 20 years old son is in poor condition.

    Plumber came on site recently and said that the pipes from the gas main are 1/2 inch pipes and we need to get a new 3/4 inch pipe all the way into the house. That is raising the quote from 3k to 4k.

    Can someone help me understand why the 1/2 inch pipe is not sufficient for a newer boiler? I’m struggling to find anything that explains this online.


Comments

  • #2
    Outkast_IRE
    Registered Users, Registered Users 2 Posts: 7,517 ✭✭✭Outkast_IRE


    Its not really anything to do with the newer boiler, it should probably of not been 15mm 1/2 pipe in the first place. The gas regulations stipulate you are only allowed a pressure drop of 1mbar from the meter to the appliance.



    The example given in the guide would be a straight length of 1/2 pipe with no bends or fittings could be a maximum of 6m long to serve a 22kw boiler.



    If you can prove the pressure drop is acceptable, 15mm for a single appliance is ok but for each bend there is a pressure drop, for each fitting there is a pressure drop. I dont know of any installer that accepts 1/2 anymore , you should also remember that if you did have only 1/2 and the calculation says your ok, you could never fit a gas stove or oven.



    The document below pg 29 and 30 are of particular relevance.



    http://www.rgii.ie/_fileupload/installer%20files/Technical%20Info/RGIIdocument.pdf


  • #3
    [Deleted User]
    Posts: 3,858 ✭ [Deleted User]


    It’s like trying to push a Elephant in to a rabbit hutch.

    Your boiler needs a elephants amount of gas but the pipework is designed for rabbits 😁 so you need bigger pipe to match the load.


  • #4
    kirving
    Registered Users, Registered Users 2 Posts: 6,296 ✭✭✭kirving


    Outkast_IRE wrote: »
    Its not really anything to do with the newer boiler, it should probably of not been 15mm 1/2 pipe in the first place. The gas regulations stipulate you are only allowed a pressure drop of 1mbar from the meter to the appliance.

    I understand the pressure drop equations and that it makes sense to use a larger pipe.

    But out of interest, is there a safety reason for this (perhaps Gaz/oxygen ratios?), or just than a boiler wouldn't necessarily run at maximum output?


  • #5
    [Deleted User]
    Posts: 3,858 ✭ [Deleted User]


    Kevin Irving wrote: »
    I understand the pressure drop equations and that it makes sense to use a larger pipe.

    But out of interest, is there a safety reason for this (perhaps Gaz/oxygen ratios?), or just than a boiler wouldn't necessarily run at maximum output?


    Every gas HE boiler must be commissioned at its highest badged capacity.
    Insufficient gas can effect the warranty, combustion and safety.


  • #6
    kirving
    Registered Users, Registered Users 2 Posts: 6,296 ✭✭✭kirving


    gary71 wrote: »
    Every gas HE boiler must be commissioned at its highest badged capacity.
    Insufficient gas can effect the warranty, combustion and safety.


    My question really is, what about a low gas flow actually causes a safety issue? Is is that excessive oxygen can cause an explosive environment (as with an oxyacetylene torch), or that low fuel ratio could cause carbon monoxide to be produced rather than carbon dioxide?


  • Advertisement
  • #7
    [Deleted User]
    Posts: 3,858 ✭ [Deleted User]


    Kevin Irving wrote: »
    My question really is, what about a low gas flow actually causes a safety issue? Is is that excessive oxygen can cause an explosive environment (as with an oxyacetylene torch), or that low fuel ratio could cause carbon monoxide to be produced rather than carbon dioxide?

    You can have light back where the flame travels back down the supply pipe but iv never seen it, it’s less likely on HE boilers due to their design, the biggest issue is incorrect combustion due to lack of gas, intermittent ignition issues.

    Also low working pressure can have a negative effect on other appliances on the same supply, not all appliances have the safety devices required in the event of low working pressure which can lead to unlit gas entering the premises.


  • #8
    kirving
    Registered Users, Registered Users 2 Posts: 6,296 ✭✭✭kirving


    Thanks, hadn't thought about it that way. So low pressure means it's more likely to go out, and potentially fill the house with unburned gas.

    Do the regulations allow for an existing 1/2 inch pipe to be used, if the pressure is confirmed as OK?


  • #9
    DGOBS
    Hosted Moderators Posts: 3,496 ✭✭✭DGOBS


    The gas regulation specify that a domestic premises gas pressure is 20 mbar (+/- 2) and that the permitted pressure loss across an installation (affected by pipe sizing and connected appliances) is 1mbar (for Nat gas).

    Some appliance will work fine with reduced gas pressure, but as Gary described above, you new boiler consumes gas in a different manner, which may affect this pressure loss.

    While you boiler uses a gas regulator, to ensure correct pressures to the appliance burner (which is below the 20mbar supplied in the line) other appliances do not, and rely on the correct line pressure for correct and safe operation. If the supply is undersized this may reduce the line pressure in the house. Resulting in under gassed appliances.

    Appliances that are under gassed (over aired) may produce higher levels of CO, and being these appliances include gas cookers for example, that are flueless, this would be an unacceptable safety risk.

    If your current gas supply to the appliance is adequate, for the appliance being supplied, and when in it's highest mode of operation, along with any other appliances on the same gas supply line, the test shows that the loss in pressure at any and all appliances is below the standing pressure by 1mbar or less, then your all good.

    But with most new HE boilers the recommendation would be a minimum of a 3/4 supply to avoid this situation.


  • #10
    [Deleted User]
    Posts: 3,858 ✭ [Deleted User]


    Kevin Irving wrote: »
    Thanks, hadn't thought about it that way. So low pressure means it's more likely to go out, and potentially fill the house with unburned gas.

    Do the regulations allow for an existing 1/2 inch pipe to be used, if the pressure is confirmed as OK?

    The regs require the correct working pressure at the appliance.

    This is tested by confirming a maximum of a 1 mb drop between the value at the meter and the value at the furthest appliance with all appliances turned on to maximum output.

    If that can be achieved then the pipe sizing has been proved irrespective of pipe size.

    It is important to feed every gas appliances with the correct volume of gas, using larger pipes makes it more likely to achieve this without doing the calculations required but as the skillset of individual RGI improve more and more home owners will be having to deal with originally incorrectly sized pipes or increases in pipe size required to feed larger capacity combi boilers.


  • #11
    FutureGuy
    Moderators, Computer Games Moderators Posts: 15,255 Mod ✭✭✭✭FutureGuy


    Appreciate all the responses everyone. The plumber did a great job on explaining things but I’m only starting to learn about this sort of thing. Couldn’t find any information to study further.


  • Advertisement
Advertisement