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Gas fitting question

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  1. #1
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    Default Gas fitting question

    Hi All,

    Before I start let me first say that I am having all this work done by a licenced gas fitter. I am just the kind of person who likes to understand the reason behind the decisions made by the various trades.

    I am hoping one of you is a gas fitter and can advise on pipe sizing for me. I am having 2 45kg LPG bottles installed along with 2 appliances. From the bottles there will be a 4m run to a T junction where our gas cooktop will be (46MJ/hr), then the pipe will continue another 4m to a Rinnai Infinity 26 Enviro hot water heater (172MJ/hr).

    The oven specifies a minimum working pressure of 2.75kpa. The water heater specifies a range of 2.75 - 3kpa.

    I had a read through AS5601 and the piece of information I seem to be missing to calculate pipe sizes is the supply pressure from the bottles. What pressure does a normal LPG regulator run at?

    The installer has suggested 3/4" copper pipe from the bottles to the T junction then 1/2" pipe to the oven and water heater. I am thinking I should spend the little bit extra and run 3/4" all the way through to the hot water system.

    Any advice is appreciated. Thanks

  2. #2
    Slow but rough Uncle Bob's Avatar
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    Default

    Quote Originally Posted by vincentvega View Post
    I seem to be missing to calculate pipe sizes is the supply pressure from the bottles.
    I'm not a gas fitter, just a gas creator

    I'll think you you'd find that pipe diameter wouldn't affect pressure much, only volume delivered.
    Now over to the gas fitters

  3. #3
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    Beckenham / Perth / WA
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    Default

    I remember being in my roof once and noticing my gasline does basically that. Large pipe from the mains up until a junction where it splits into two small pipes, one for the stove and one for the hot water system. Can't say I've ever noticed any lack of power.

    I do know that when I asked a plumber who was doing some work here once about getting a permanent barbecue set up out the back near the hot water system, he said that the pipe would have to be upgraded up to that point. So I'd say if you wanted to future proof your line, then get the larger size, otherwise your plumber would know what the go is.

  4. #4
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    Feb 2013
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    Metford NSW Australia
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    Default LPG Pipe Sizing

    Hi Vincentvega,
    As you can tell from the consumoption rating of the Infinity 26, it has a thirsty little burner.
    You will also find it has a 3/4" inlet for gas as well as hot and cold water.
    You should never have supply piping smaller than the inlet fitting size.
    You should then run minimum 3/4" copper all the way to the water heater.
    Then take a 1/2" branch off to the cooker.
    The water heater will not achieve correct operation with smaller pipe.
    The same goes for the water piping. Take 3/4" all the way to the inlet of the heater and all the way from the outlet to the last branch on the hot water line.
    Also use quality insulated piping for the hot line.

    Hope this helps.
    Stephen
    Lic. PDGL

  5. #5
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    Default

    Quote Originally Posted by Uncle Bob View Post
    I'm not a gas fitter, just a gas creator

    I'll think you you'd find that pipe diameter wouldn't affect pressure much, only volume delivered.
    Now over to the gas fitters

    The pipe diameter will affect pressure drop, which will affect the pressure at the appliance. Hence my question

  6. #6
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    Thanks guys. I will ask for a minimum 3/4" to be run all the way to the heater. I may add a BBQ outlet when we replace our deck, so another reason to go big that I didnt think of.

  7. #7
    Golden Member
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    Default Bottle gas

    Get ready to chew through the bottles! If you can get re-supply through gas tanker rather tha bottle replacement, I'd consider using the much bigger bottles (can't find the size, but they must be 200kg). I can't do that, my neighbours can, and my cost of LPG energy/Mj is about twice theirs.

    Just a thought!

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