28mm gas pipe anywhere on run ? to up the delivery

[JPC]

hi

When doing a gas run i have been told that if a 28mm is required then, it can go anywhere...nearest to meter the better but its not necesarily got to be 28mm to the meter...it could have say 22mm for 500mm or similar and then up to 28mm.....

is this right?

ie my mate fitted a combi..did about 500mm in 22mm from the meter (due to easy of bends etc) and then uped it to 28 for 3 meters./ he is corgi
whereas i'm trying to get my 70 days evidence to then do my corgi

 

[JPC]

yes, so the having worked out the resistance it requires some 28mm.
now back to my question, does it matter where in the run its placed

 

[gasmataz]

straight off the meter is best

 

[Biggles..]

Makes no difference, i say this having attempted it and achieved satisfactory results. 22mm for 10meters and then 28 for 15mm to boiler.

There is evidence posted on here that due to the way the reducers face in relation to the flow of gas that certain resistances have different effect( D Halisham i think)

 

[gasmataz]

it all depends what is on the gas route if you have say a fire and a cooker then a boiler you need to work out there gas needs and make sure you carry enough gas to the boiler etc. thats why it's best leaving it to someone who knows what there doing you could end up over/under gasing other appliances. i always go big off the meter for as far as i can go and then test pressure at appliances remember if its a boiler you normally got 2 mb to play with (18-20) but check mi's

 

[Agile]

D Hailsham usually gives good legal advice.

There is a fluid dynamics lecturer ( called Vijay or similar ) who advised us that a transition from 28mm to 22 mm gives slightly less restriction than a trasition from 22 mm to 28mm. Thats rather counterintutitive !

However, as most gas supplies to boilers start at 22mm and end at 22mm there is little difference where the larger pipe is located.

However, most gas installers have this ( false ) idea that the large pipe is best at the meter end. It usually works out that way because pipework at the boiler end is usually hidden within a kitchen.

The place where its useful to have 28 mm is where there are elbows fitted!

Tony

 

[doitall]

The resistance is in the length plus fittings, 3m of 22mm will deliver the same volume as 14m of 28mm, therefore it's quite acceptable to run the 1st metre or so from the meter in 22mm.

Incidentally 3m of 22mm excluding bends etc, exceeds an U6 meter capacity, so being larger is pointless.

 

[gasmataz]

Just work it out if you do the maths you might have to go of the meter with the larger pipe if not then great.

 

[JoeMar]

this is a good link for anyone who is interested in how to work out pipe sizes.

http://www.cda.org.uk/megab2/build/...een the ends, for gas of relative density 0.6

sorry if this has been posted previously.

 

[gas4you]

I think the only one so far who who may be right is gazmataz.

If there are no other appliances using the gas supply, then it shouldn't matter.

If there are then the 28mm should be at the start of the run as this will be where the greatest volume of gas is going to be demanded from with all appliances on full.

Even this way though you should be able to get away with at least 3M of 22mm off the meter.

If you calculate the pipe size correctly then this will answer all your questions.

 

[buryboy]

I have two guys looking for my work
Going to fit a worcester Greenstar 42 or Baxi duotec 40 combi

One guy intends to put new 28mm all the way from gas meter to new boiler ( about 15 metres the way he intends to go) ( see my other post re routing on outside of house) - other one says only 1.5 to 2m of new piping is required , this to be at the boiler end , and only 22mm.He is also proposing to put in bends to achieve this length ( to avoid disrupting first floor bedrooms) and i'm concerned it won't be enough for these big boilers

Would it helped if he used 28mm or instead put the new pipe just at the meter end ( or indeed do both ?)

Can you help a confused non-techy ??

Thanks
Graham

 

[ChrisR]

Can you help a confused non-techy ??

I'm sorry to see there's some incorrect information in some of the posts .

Corgi specify a maximum pressure drop between the meter, and appliances, when they're all working flat out. That's 1mbar, not 2 as given above.

To achieve that, the resistance of the pipes has to be low enough. How that's achieved, makes no difference, so larger pipe could for example come further from the meter than smaller, if the installation were easier. The meter outlet is usually only 22mm anyway.

Anyone with experience knows that the tables of resistance are very over-optimistic, and choose their pipe sizes accordingly. Ultimately it makes no difference what the tables say, it's that 1 mbar which matters.

One of your installers is being more pessimistic that the other, very possibly with good reason.

If you're concerned that the installer is guessing, and just insisting, "it'll be all right", ask him how he's worked it out. It shouldn't take more than a few minutes. If he can't show you, be worried. At the quotation stage you can ask him if he's prepared to show you.

 

[gas4you]

Good advice Chris.