Gas pipe diameter

[zero]

I know building regs state that there must be a 22mm pipe from the meter for the boiler. However where my old boiler is the last run to is 15mm. This vanishes under the floor and how far away it joins the 22mm is unknown. As I am on the third floor of an old house split into flats and the pipes are cemented into the and I cannot really rip them out as they run through neighbours flats walls what can be done. Is this small last run of 15mm allowed as it is probably only a meter or 2.

Thanks

Zero

 

[Bernie2]

Hmm!

Not sure exactly what you mean. But in general a boiler feed should be about 22mm right up to the last meter or less from the boiler.

Unfortunately its not that simple either. If your on the 3rd floor you've got to know the length and number of fittings on the length from the meter to the boiler as well as anything else supplied off the same pipe.

It may be, you may even have to upgrade to at least 28mm or even 32mm and then reduce down. A good explanation is given on the copperboard site under gas pipe sizing.

Basically its got to do with flow resistance and use. The more users the bigger the pipe required. The further away from the meter you are the bigger the pipe you require.

So you may be the only user, but still have resistance you need to overcome.

That may sound daft, but its because in a small pipe, more of the gas stream is in contact with the walls of the pipe and so has to overcome more of the walls resistance. In a big pipe the centre of the gas stream doesn't touch the walls so it has less resistance to overcome.

Its the same for a spark and his cables.

To calculate it properly of course, you need quite a bit of info, so that is why I said it may help to look at the copper board site, it probably gives you details in a more orderly way than a forum.

 

[Plucky]

I hope your not thinking of undertaking the work yourself

 

[zero]

I hope your not thinking of undertaking the work yourself

No definately not. I am just trying to get an idea of costs as have a number of companies going to offer me quotes and just trying to get all the info I can to make sure they are telling me the right things

 

[newbie1]

its not actually regulations to have a 22mm feed but rather whether 15mm will flow the required amount of gas for the boiler and as its an old house with pipes in the walls it would be impossible to do a correct pipe sizing exercise
you might be lucky most old houses the pipes in the wall are of sufficient size but and its a big but if you need larger pipes then it will mean a new run from the meter
do you have a sep meter or is there 1 meter that serves whole property

 

[zero]

its not actually regulations to have a 22mm feed but rather whether 15mm will flow the required amount of gas for the boiler and as its an old house with pipes in the walls it would be impossible to do a correct pipe sizing exercise
you might be lucky most old houses the pipes in the wall are of sufficient size but and its a big but if you need larger pipes then it will mean a new run from the meter
do you have a sep meter or is there 1 meter that serves whole property

I have a separate meter which was just replaced with a new one by the gas company. There 4 flats each with own meter. Will it help having a separate run. Also I have been asked if I had a boiler in mind by my fitter. I have done some research and looked at the Vaillant ecoTEC pro 24 as it has a 15mm gas connection I think however will it be enough for a 1 bed flat as want to run a shower off it.



Thanks


Zwero

 

[stevetheplumber]

where is your meter ?if its down three floors at the front of the house and your third floor with boiler at the rear youralmost certainly going to need 28mm pipework from metter to boiler
mormally we run externally up the front of a building then in thru the floor void but im dealing with victorian houses that have been converted to flats

 

[zero]

where is your meter ?if its down three floors at the front of the house and your third floor with boiler at the rear youralmost certainly going to need 28mm pipework from metter to boiler
mormally we run externally up the front of a building then in thru the floor void but im dealing with victorian houses that have been converted to flats

The meter or so in in the kitchen from the floor to the current boiler. I am going to lift a floor board tomorrow and hopefully it is joined to the large bore pipe just below the floor boards.

 

[stevetheplumber]

didnt quite understand that last post basicly where is your meter in relation to where the boilers going to be ? most boilers have 15mm inlets its the pipe to it that needs to be checked

 

[zero]

didnt quite understand that last post basicly where is your meter in relation to where the boilers going to be ? most boilers have 15mm inlets its the pipe to it that needs to be checked

The pipe going up the wall is mm from the floor level to the back of the boiler. I believe it joins a 20mm under the floorboards but I am going to check this.

 

[newbie1]

right if you have a meter in your flat and it only serves your flat no prob you can just run a 22mm of the meter which then is reduced at the boiler to 15mm
the vaillant is a nice little boiler and if your just running a 1 bed flat will be fine check flow rate first though and tbh if its just to run new supply from meter in your flat and rip out old boiler and replace with new one then 2 days max incl powerflush prob around 600.00 for a straightforward job

 

[migoplumber]

i would suggest a new gas supply line from meter to your flat, i can see a problem, and a probable problem from your comments. firstly that your gas line is cemented into other peoples flats (thats worrying and definetly n.c.s) therefore your installer would be unable to make a new install to the existing supply without breaking gas regs.
probable problem. dont renew the main, install the new boiler when installers gas rates appliance and it dosnt pass, your wide open to be charged the earth by him for a new main.
replace the main, then get a new boiler of your choice, (not one that your obliged to install because of your current instalation)

good luck
shaun

 

[newbie1]

ime guessing he has his own meter in the flat as it would be pointless having a meter in his flat that serves other flats so if the meter is in his flat it will have the correct pressure incoming
this should then be fine to run a new 22mm supply into 15mm
first step is to get a gas engineer to come to the flat and check your pressure at the meter with no appliances running and if it is between 19-23mb then you will not have a problem simply get them to run new supply from outlet of meter to the boiler and if neccsy to your cooker (if its gas)
its only going to be a short run so depending on standing pressure test if its fine then use elbows etc if pressure is low try to avoid using too many elbows and try bending the pipes

 

[Puddle]

Think you mean check working pressure at boiler,newbie
Standing presure could be ok however once appliance turned on could fall right down ie if pipework to small,faulty governor
If standing presure down on test,supplier should be called as could be dangerous

 

[newbie1]

what i mean is if his standing pressure incoming is between 19-23 preferably 23mb then his incoming supply is fine and the the regulator is doing its job then if he runs the new supply in 22mm and 15mm from the meter he should be fine as it likely that the incoming pipework up to his meter is one of 2 things
1/newly run(unlikely)
2/old orig iron which will be of a sufficient diameter although not ideal as its in the walls and floor but then again most old iron pipework is
its higly unlikely landlord will swallow for the cost of running totally new pipes from the main meter to all 4 flats in 28-32mm as the cost would be huge
yes he could also gas rate his orig boiler but not sure if that is working
but basically he just needs to get the standing pressure tested first and if thats fine then likely he wont have a problem with running new supply
just trying to stop him having his pants taken down

 

[Bernie2]

I still can't make out whether he has a Primary meter or a Secondary. If its a Secondary meter then he may be better off with a system boiler set up than a combi. But you would have to gather info to find out what the options are.

 

[Puddle]

The standing pressure tells you didly poop apart from showing gas present
It definatly does not tell you the regulator is ok or that the incoming gas supply is fine
and its not going to stop getting his pants taken down.......shaving cream rubed in his bum cheeks.......... his chest shaved.........oh sorry.......getting carried away

 

[newbie1]

surely the standing pressure shows regulator is doing its job as isnt it the pressure incoming anything from between 75mb and 2 bar for low to medium fed meter
at the end of the day my guess is that this is not a primary meter it is a secondary meter so landlord can bill each unit he lets out
and as such will prob be fine with a 22mm into 15mm at new boiler
worth gas rating orig boiler to see if its getting good pressure

 

[Bernie2]

Err!

On a Primary/Secondary meter system you only have about 20-25mb in the main riser, not 75mb.

The 75mb - 2 bar pressure is usually a gas meter governor inlet service side pressure, for individually mains connected meters. But that would be at the inlet to the Primary meter not the Secondary meters, they are just really governor less flow meters.

If you use Secondary meters on domestic, you usually have to treat the whole place like one big house and work out sizes as though its one house, so that each appliance in every flat gets a minimum of 20mbar with everything in the block of flats working flat out.

Okay so you can drop 1mbar, but that is only an allowable drop not a standard.

It works a bit like:

If you can only suck so hard up a straw, and you only get 1 pint of water in a minute up the straw, but you want more than a pint in a minute, you get a wider straw.

In this case increase the flow.

So to work it all out, you need a load of figures, resistances and route descriptions which basically, we haven't got.

If however your on governed down individual supplies with 20-25mb at the outlet and your boiler position is only a few feet away from the meter. Then you should be okay with 22mm or even 15mm to the boiler. Must admit I prefer it in 22mm and reduce down close to the boiler.

 

[newbie1]

that makes sense so if at primary meter say 75mb and 21mb on outlet riser as long as primary meter regulator is working then they all should be getting between 19-23mb at their meters and if we assume orig boiler was getting sufficient flow then a new boiler which will have new pipework of 22mm-15mm(i blve for a short run the vaillant wld be ok on 15mm)but better on 22mm reducing to 15mm
and if the pipe can be bent instead of elbows even better

 

[Bernie2]

Hi! Newbie1

If the riser pipe to the Secondary meters is sized correctly and all appliances in the whole block are getting 20mb - 25mb when all are full on. Its okay.

But we don't know the size of his former boiler it may only have been very small requiring 4 or 5kW and if he then puts a small combi on that requires say 23kW you can understand the potential problems.

The chances are when he gets it fixed, it may look okay, but when the tenant's on the next floor up, come to use their appliances its a case of "Where has the gas gone?"

In point his system may be demanding 4 times as much gas as it was before.

But then of course, he may have had a bigger boiler, you just don't know so many things.

He could of course be on a system whose gas riser is adequatly sized for any future uses. In which case as you say he would have no problem.