undersized gaspipe in listed building

[sooey]

I went to look at a job which is a combi swap in a large listed building which has been converted into flats. It was obvious that the gas supply was undersized and would have to be upgraded. This would be very awkward to do running internally, but could be done quite easily if the pipe could be run up the side of the building externally. Does anybody know what the likelihood of getting permission for this might be, given that it's a safety issue and the current installation is obviously well under gassed? I didn't check the pressures as the owner was not present and I
couldn't even find the ecv (if there is one, which I doubt) or the point of entry into the flat. At the moment the gaspipe is run across the cellar from the external meter and the up to the second floor flat and has an effective length of about twenty metres all in 22mm until it enters the flat.

 

[giblets]

20m of effective pipe length of 22mm copper should manage about 30kw input with a 1mb drop Does the 20m include the fittings?

Secondary isolating valve has to be installed with suitable label.

First I think you need to confirm the existing pipe is actually undersized in the usual way.

Obtaining permission for routing the pipe externally would be the owner's problem not yours.

 

[Agile]

20m of effective pipe length of 22mm copper should manage about 30kw input with a 1mb drop

What formula have you used for that?

Tony

 

[giblets]

From pipe sizing chart:

20m(effective length inc. allowance for fttgs) of 22 will pass 2.9cu m/hr ~ 2.9 divided by 0.09 = 32.22kW.

Have I got it wrong?

 

[sooey]

giblets thanks for reply, it's definitely undersized, there's a 29 kw combi there already and a gas fire and hob, also the 20 meters was just to the point of entry into the building. theres the internal pipe runs to add on to that as well. i know it's more the owners problem than mine, but as a relatively new entrant into this game I am constantly surprised at some of the installations I see that don't come anywhere near to the standards that were told to us as gospel during acs training etc. I wouldn't dream of putting a combi onto that installation as it is at present and then signing it off with my name, and I can see the owner not wanting to get involved with all the hassle of upgrading the pipe, so it looks like yet another job out the window.

 

[giblets]

I am constantly surprised at some of the installations I see that don't come anywhere near to the standards that were told to us as gospel during acs training etc.

Welcome to the real world

so it looks like yet another job out the window

Don't worry - there will be lots more (and easier ones too)

 

[Agile]

Have I got it wrong?

Thats an interesting question! Certainly you have correctly applied the formulae.

However, many like Chris and I visit a lot of existing installations where we find that the actual pressure drop greatly exceeds the calculated figure. Chris suggests that an additional 70% is needed and I would say 20%-30% as a minimum when I am installing.

I think that the answer is that the tables are based on a continuous length of tube whereas all soldered joints have had the tube cut with a pipe slice which introduces a discontinunity and then add some solder runs inside and it becomes quite different from the "best case" calculated figure.

Some installations I visit obviously have a serious restriction but the circumstances dont permit me to dismantle to find it. We have all found pipes virtually blocked by jointing compound, PTFE tape, solder runs or sulphide deposits to add to the problem.

I also sometimes wonder if two elbows close together cause more restriction than they would if seperated.

I always check gas pipe pressure losses where possible by measurements as I find calculated values to be so different in some cases on existing installations.

Tony

 

[giblets]

I would fully agree with your comments, Tony. I have also come across some "interesting" situtations in the 30 odd years I've been doing this job (non-BG )

Based on the further info given in Sooey's second post I doubt I would have selected 22 - more like 35 As you say, each job has to be looked at differently. And, of course, the tables are for an ideal world aren't they.

I always check gas pipe pressure losses where possible by measurements as I find calculated values to be so different in some cases on existing installations

Been there, done it, had to rectify it.

Sooey, If the owner can't be bothered with the hassle of upgrading the pipework it looks like he/she is stuck with the existing boiler. You are probably best out of that one.

 

[sooey]

It's not so much that the owner can't be bothered, it was just some idle thoughts I was having, I'm waiting for my mate who is arranging the job to talk to the owner and wondered in the meantime what the issues would be in the case of a listed building.My thoughts were to take it across the basement (about 8 meters) in 35, and then out and up to the point of entry in 28 and the rest in 22. Anyway thanks for replies, i'll wait to see what the owner says.

ps He'll probably think it's just another gasman trying to think up ways to get money out him.

 

[doyle]

giblets thanks for reply, it's definitely undersized, there's a 29 kw combi there already and a gas fire and hob, also the 20 meters was just to the point of entry into the building. theres the internal pipe runs to add on to that as well. i know it's more the owners problem than mine, but as a relatively new entrant into this game I am constantly surprised at some of the installations I see that don't come anywhere near to the standards that were told to us as gospel during acs training etc. I wouldn't dream of putting a combi onto that installation as it is at present and then signing it off with my name, and I can see the owner not wanting to get involved with all the hassle of upgrading the pipe, so it looks like yet another job out the window.

tuff for him he aint allowed to have undersized so you can still terminated the supply if the drop is to much, so you still get the work lol

 

[gas4you]

From pipe sizing chart:

20m(effective length inc. allowance for fttgs) of 22 will pass 2.9cu m/hr ~ 2.9 divided by 0.09 = 32.22kW.

Have I got it wrong?

Will also depend if any other appliances are coming off it, eg if 3 appliance then multiply pipe lenght by 3 so they get .333 mbar drop each

I never go more than 12/15M equivalent length for a 30Kw boiler

 

[giblets]

I know that now, Dave, after the OP's 2nd posting. First posting just said 20m effective length.

I find it easier to divide the total (inc ftgs) length of pipework by the charted maximum length which gives the pressure drop for each section. Add the relevant sections together and they should come to under 1mb.

 

[ChrisR]

On one installation I even put a test point each end of the actual pipe run, which was a LOT of 28mm going to a 30kW boiler. All the elbows were the "slow" type and really carefully scraped out with a knife to remove any protrusion into the bore.
It's so long ago I can't remember the details, but I know the tables predicted a drop of just under 1mbar, and I got just under 2.

Based on the further info given in Sooey's second post I doubt I would have selected 22 - more like 35

Sounds about right to me!

As far as the Listed Building bit is concerned , it's obviously every one on its merits inconsltaion with "the authorities" which may include some spotty sociology graduate who thinks his opinion is real. The front of the building will be out of bounds, but the side is likely to be possible if you use brass clips and can pick a tidy route.


To beginners - others have it covered but a case in point on pipe sizing is a current problem I'm looking at.
35kw boiler (suprima 120) with 1" iron barrel off the meter, which disappears into the fabric to re-emerge as 22mm, with a foot of 15mm into the boiler. The drop might have calculated out to about 1mbar, but it measures 7mbar. There are fires and cookers on the way, so you can take pressure readings (without drawing gas) at those, and it appears that the drop is distrubuted fairly evenly across the length.
This is a basement of a rather nice terraced 5 floor house which has marble tiles above the probable pipe run, and concrete floors below. So the only (?) way to get pipe from the front of the house to the back is to surface run it. The 35mm(big fires) required will look really good.