We're aware that some users are experiencing technical issues which the team are working to resolve. See the Community Noticeboard for more info. Thank you for your patience.
📨 Have you signed up to the Forum's new Email Digest yet? Get a selection of trending threads sent straight to your inbox daily, weekly or monthly!

sizing gas pipe for boilers

Options
Got 2 quotes on the replacement of my combi-boiler.
One of them mentioned that gas pipe needs to be 22mm. However, the other didn't even mention gas pipe at all.
I assume the latter just assumed if the old boiler works, the same pipe will work for the new boiler.
I don't know much about combi-boilers, so can anyone explain to me the possibilities if the gas pipes is not increased to 22mm (parts of it is already
22mm, but not all of it)? I just think the gas pressure may not be enough, but what's the resulting situation?

Furthermore, how can I estimate how big the gas pipe need to be (in case even 22mm is not enough in the future), any quick guides?

Thanks everyone

Comments

  • ormus
    ormus Posts: 42,714 Forumite
    15mm gas pipe will only carry 15000 btu,s.
    so vitually all modern domestic gas boilers will require a 22mm gas supply pipe.

    esp if feeding say a gas cooker too.
    Get some gorm.
  • Gloomendoom
    Gloomendoom Posts: 16,551 Forumite
    Part of the Furniture 10,000 Posts Combo Breaker
    ormus wrote: »
    15mm gas pipe will only carry 15000 btu,s.
    so vitually all modern domestic gas boilers will require a 22mm gas supply pipe.

    esp if feeding say a gas cooker too.

    Strange. My boiler input is 100,000 to 114,000 BTU's

    It is fed by a 15mm gas pipe.


    My house has solid stone walls, no double glazing and it's very warm.
  • gas4you
    gas4you Posts: 2,602 Forumite
    Ormus, you are getting confused with the heat carrying capacity of 15mm pipe for radiators.

    Gas pipe sizing has to be done taking into account the input power of all the appliances, length of pipe run, number of elbows/bends in the pipe etc etc.

    Gloomendoom, unless your boiler is withing approx 3m of the gas meter, your gas pipe is undoubtedly undersized for that power boiler.

    Just because it may seem to work ok, the power input will be less than it needs to be and the pressure drop between meter and appliance will be greater than regs allow.
  • Gloomendoom
    Gloomendoom Posts: 16,551 Forumite
    Part of the Furniture 10,000 Posts Combo Breaker
    edited 1 March 2011 at 12:50AM
    gas4you wrote: »
    Gloomendoom, unless your boiler is withing approx 3m of the gas meter, your gas pipe is undoubtedly undersized for that power boiler.

    Just because it may seem to work ok, the power input will be less than it needs to be and the pressure drop between meter and appliance will be greater than regs allow.

    I've been told this before. The meter is in the front garden and the boiler is in an an outbuilding at the back of the house. Part of the run is 22mm but the last 10/12m are 15mm pipe. Theoretically the boiler (an ancient 70's Potterton) is well matched to the size of the house and, in practice, it heats it perfectly well even in the coldest winters.

    If the power in was too low, then one would expect the power out to be correspondingly low. It isn't. :huh:
    .
    .
    .
    .
  • gas4you
    gas4you Posts: 2,602 Forumite
    Yours is a very common scenario with boilers fitted years ago.

    The chances are the boiler was oversized when fitted anyway. Even if the burner pressure may be set correct the boiler output may be low.

    You need to gas rate the boiler. If you have a metric meter, see how much gas is used in 2 minutes. If am imperial meter, see how long it takes for one revolution of the dial, then post back results.
  • Gloomendoom
    Gloomendoom Posts: 16,551 Forumite
    Part of the Furniture 10,000 Posts Combo Breaker
    gas4you wrote: »
    Yours is a very common scenario with boilers fitted years ago.

    The chances are the boiler was oversized when fitted anyway. Even if the burner pressure may be set correct the boiler output may be low.

    You need to gas rate the boiler. If you have a metric meter, see how much gas is used in 2 minutes. If am imperial meter, see how long it takes for one revolution of the dial, then post back results.

    Cheers. :)

    I'll give it a go at the weekend. I don't run it with the boiler thermostat turned up full. I suppose it would use more gas if I did.
  • User2050
    User2050 Posts: 20 Forumite
    Thanks for your input.
    I now understand what really matters here is the gas pressure, am I right?
    If gas presure is low, what will happen? I can think of,
    1. lower input power, hence lower output power --->
    2. bath water is not hot or takes longer to get hot; and heating is not warm enough.
    what else? Will the boiler stop functioning? - as I am starting to think maybe my current boiler looks sick just because of this - not enough gas pressure?

    Any gas engineer willing to explain?

    Thanks again
  • BaldPlumber
    BaldPlumber Posts: 145 Forumite
    With the hot water running, take a reading at your meter as in #6 and post the results back. Someone will calculate the heat input for you, but will not be able to advise on pressure drop from the meter.
This discussion has been closed.
Meet your Ambassadors

🚀 Getting Started

Hi new member!

Our Getting Started Guide will help you get the most out of the Forum

Categories

  • All Categories
  • 350.9K Banking & Borrowing
  • 253.1K Reduce Debt & Boost Income
  • 453.5K Spending & Discounts
  • 243.9K Work, Benefits & Business
  • 598.8K Mortgages, Homes & Bills
  • 176.9K Life & Family
  • 257.2K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 16.1K Discuss & Feedback
  • 37.6K Read-Only Boards

Is this how you want to be seen?

We see you are using a default avatar. It takes only a few seconds to pick a picture.