Adding 3 metres of 28mm pipe at the end of a 15 metre 22mm run

[boilerwoes]

All,

First time poster, long time reader!

I need some advice before I get some quotes to resolve an issue. I found out a couple of days ago (from a boiler engineer) that the gas inlet working pressure at my boiler is too low (approx 13.5mbar). I haven't got precise figures, but apparently the working pressure at the gas meter is approximately 20mbar, but the boiler engineer was not precise about it. The system is gas tight, so no leaks. System has 22mm pipe to a boiler and to a gas hob. The 22mm reduces to 15mm for the last 0.5m for the boiler, and 1m for the gas hob.

Replacing the 22mm pipe with 28mm pipe from the gas meter is going to be hard due to obstacles etc. One option could be to increase the pipe size for the last 2-3 metres of the 22mm run, just before it enters the boiler, but am not sure if this will help reduce the pressure drop?

In terms of length of 22mm pipe - there is approx 15 metres of 22mm pipe between gas meter and boiler with about 10 corners and 1 tee. From the tee, there is approximately 3 metres of 22mm pipe before reducing down to 1 metre of 15mm pipe going into a hob.

Thanks in advance.

 

[Billy Bob Bob]

Replacing the 22mm pipe with 28mm pipe from the gas meter is going to be hard due to obstacles etc. One option could be to increase the pipe size for the last 2-3 metres of the 22mm run, just before it enters the boiler, but am not sure if this will help reduce the pressure drop?

will help,would try replacing the 15mm to boiler with 22 first but it does need 28 mm installed by the sounds of it,within 2-3 mtrs of the boiler should cure the issue but the engineer needs to do his/her calcs on pipe sizing sounds along way for 22mm what kw rating is your boiler

 

[boilerwoes]

Hi Gas man,

Thanks for the quick response. The boiler is a (Vaillant ecotec plus 831) 31kw one. 15mm can't be changed to 22mm as the boiler has to have a 15mm pipe feed in - so this is the shortest possible run to be 15mm.

In terms of gas pressures within piping - am I correct in assuming that we can replace any section of a 22mm pipe with 28 mm pipe to gain a better (reduced) pressure drop, and it doesn't have to start from the gas meter?

Someone I know indicated that the 28mm pipe has to start from the meter otherwise it doesn't make sense increasing it the pipe size after an initial 22mm restriction (as you have reduced the pressure due to starting off with a 22mm pipe). I have read somewhere else (though it wasn't conclusive) that gas behaves differently to water so if you do add a larger pipe diameter (28mm) after a run of 22mm, or in between a run of 22mm, then it should help.

Lot's of conflicting advice! ;-)

 

[Billy Bob Bob]

In terms of gas pressures within piping - am I correct in assuming that we can replace any section of a 22mm pipe with 28 mm pipe to gain a better (reduced) pressure drop, and it doesn't have to start from the gas meter?
​no that advice is wrong,28mm must start at the gas meter and run as far as the pipe sizing has been calculated

 

[boilerwoes]

Ahh, ok - slightly confused by your earlier post:

will help,would try replacing the 15mm to boiler with 22 first but it does need 28 mm installed by the sounds of it,within 2-3 mtrs of the boiler should cure the issue but the engineer needs to do his/her calcs on pipe sizing sounds along way for 22mm what kw rating is your boiler

When you indicated that it needs 28mm to be installed, were you indicating that this has to be from the meter, rather than the last 2-3 metres of run, just before the boiler?

 

[bill577]

In terms of gas pressures within piping - am I correct in assuming that we can replace any section of a 22mm pipe with 28 mm pipe to gain a better (reduced) pressure drop, and it doesn't have to start from the gas meter?
​no that advice is wrong,28mm must start at the gas meter and run as far as the pipe sizing has been calculated

think you will find that the advice is correct, increasing the pipe size anywhere on the run will decrease the pressure loss.

 

[tamz]

Ask your gas man to work it out. He has all the stuff he needs to calculate it in his expensive notes.

 

[tamz]

think you will find that the advice is correct, increasing the pipe size anywhere on the run will decrease the pressure loss.

But you'll need an electronic guage to 2dp to be able to read the difference in what he wants to do.

 

[Gray0689]

Gas is not like water increasing the pipe size anywhere on the run will increase the volume of gas (more gas going to appliance) but if the pipework can be increased in size it would be best practice to come from meter

 

[mickie]

ive also read that adding a larger pipe anywhere in the pipe line will increase the working pressure,

 

[bill577]

ive also read that adding a larger pipe anywhere in the pipe line will reduce the working pressure,

where did you read that ?

 

[boilerwoes]

Hmm, interesting (and different) thoughts from you guys. Thanks for all chipping in. The latest thinking seems to be that increasing pipe size anywhere in the run will increase volume, but potentially decrease working pressure at the appliance (in this case the boiler), which is the exact opposite of what I am trying to achieve (increase working pressure at the appliance)!

 

[Gray0689]

ive also read that adding a larger pipe anywhere in the pipe line will increase the working pressure,

How??

 

[mickie]

you quoted me too fast haha, i mean increase the pressure, its getting late.. think its kirkgas that said it would increase the pressure and it doesnt matter where the pipe goes and isnt he a lecturer

 

[Gray0689]

No decrease pressure loss

 

[Gray0689]

If pipe increased in size you will get more volume ie more gas going to boiler this increases working pressure as you need but as said still needs calculated properly

 

[Billy Bob Bob]

Hmm, interesting (and different) thoughts from you guys. Thanks for all chipping in. The latest thinking seems to be that increasing pipe size anywhere in the run will increase volume, but potentially decrease working pressure at the appliance (in this case the boiler), which is the exact opposite of what I am trying to achieve (increase working pressure at the appliance)!

as said from the meter in 28mm then reducing to 22mm but your installer will work out what the correct size and how far it needs running in there gas calcs

 

[mickie]

gasman so what do you make of everyone else saying its ok to have the increased pipeside anywhere in the run ?

 

[tamz]

The difference between water and gas is water cannot be compressed. Gas can.

 

[boilerwoes]

as said from the meter in 28mm then reducing to 22mm but your installer will work out what the correct size and how far it needs running in there gas calcs

Hi Gas man, thanks - the issue is that without digging up the wall, replacing 22mm with 28mm from the gas meter is not realistic - the less intrusive aspects are either at the end of the run (the last 2-3 metres before boiler) or somewhere in between which we could get access through floor boards, but it will be tough to get the first length from the meter in 28mm.

 

[Billy Bob Bob]

gasman so what do you make of everyone else saying its ok to have the increased pipeside anywhere in the run ?

you cant just chuck a length or two of 28mm anywhere on a run,it has to be from the meter otherwise whats the point?

 

[mickie]

have you read that somewhere or just assuming thats how its done ? my thinking was the same as yours but changed my mind when i read kirkgas saying its ok for the 28mm to go anywhere in the pipeline, to up working pressure

 

[Billy Bob Bob]

no its experience take a straw twist it in the middle you will struggle to pull air through it same effect as taking 22mm from the meter and putting a bit of inch in then going back to 22mm i dont agree with kirks comments

 

[GQuigley67]

its the total resistance of the pipework, less resistance in 28mm than there is in 22mm so if you put 28mm anywhere in the pipework then their is still less resistance and less pressure drop so i think kirk is right on that one

 

[LegionellaSlave]

I agree with you gas man. A lad i worked with ages ago got a better pressure by replacing a few 22mm elbows with bends and 28mm elbows. I dont know if the 28mm elbows helped but I'd think they would have less resistance than 22mm ones.

 

[cr0ft]

It matters not a jot where you increase the pipe size. Increasing the diameter of the pipe at any point along the run will decrease resistance to gas flow and thus increase the working pressure at the appliance. Resistance of the pipe and the laws of thermofluids apply to natural gas/LPG in exactly the same way as any other gas/liquid travelling along the pipe.

 

[kay-jay]

i've been told by a few gas engineers that if you can't increase diameter from meter then do it at appliance end, they call it reservoiring and it helps deliver working gas pressure in otherwise low pressure supplies

 

[fuzzy]

Hmm, interesting (and different) thoughts from you guys. Thanks for all chipping in. The latest thinking seems to be that increasing pipe size anywhere in the run will increase volume, but potentially decrease working pressure at the appliance (in this case the boiler), which is the exact opposite of what I am trying to achieve (increase working pressure at the appliance)!

why would it do that any increase in diameter will 'help' the gas get the the appliance and therefore pressure and flow rate are better

 

[boilerwoes]

why would it do that? remember the working pressure is related to thee gas govener

I don't know - just trying to summarise the points from the posts. Looks like the later posts say that increasing pipe size anywhere will increase volume, decrease resistance and increase working pressure at the appliance. The issue I am facing is that the pressure drop from gas meter to boiler is too great (around 6mbar) so am trying to determine ways of reducing this pressure drop. I am assuming the gas supply people won't change the governor to increase the gas meter pressure to above 22mbar?

 

[GQuigley67]

6mbar drop has nothing to do with the gas board, its your installation your engineer should sort this

you may need more 28mm than the last 2-3m aswell

 

[Gray0689]

6mbar drop has nothing to do with the gas board, its your installation your engineer should sort this

you may need more 28mm than the last 2-3m aswell

Agree

 

[bill577]

have your boiler gas rated and the inlet pressure checked on the hob, if the gas rate on the boiler and pressure drop on the hob are within limits leave the pipework as it is, the installation would be classed as NCS.

 

[boilerwoes]

6mbar drop has nothing to do with the gas board, its your installation your engineer should sort thisyou may need more 28mm than the last 2-3m aswell

Understood. Just responding to fuzzy's post (look at the text i quoted) about the governor. I think recent changes to the system as part of a recent period of building works have resulted in a both job (we eventually kicked out the builders) so am left o pick up the pieces. I have an RGI coming to look at it but wanted to make sure I did some research first. The reality is that it will be tough to replace anything other than the last 2-3m with 28mm pipe. Perhaps a middle section of about 3m could also be replaced but that is about it without having to dig up walls (which you can understand I would like to avoid). This gives 5-6m of 28mm upgraded from 22mm (but not starting at the meter). But it generally sounds like upgrading sections of pipe to 28mm will help even if in the middle and end of the run (although a number of you have disagreed with that, so how do I convince my RGI if he disagrees as well).

 

[bill577]

Is this a new boiler install ?

 

[boilerwoes]

Is this a new boiler install ?

No, been there a couple of years and pressure drop was fine before building work. Recent building work re routed a pipe and I asked them to ensure it was 22mm rather than the original 15mm for part of it. It is possible the measurement at the boiler taken by a boiler engineer a couple of weeks ago was incorrect so it may not be a 6mbar drop, but either way, the drop is high! I just dont understand how they could have introduced a big drop as essentially run is similar to before. Either way the builders are not coming back as I kicked them out for other shoddy work so they won't be solving it. Am hopeful that only sections can be replaced to fix the problem.