22mm to combi boilers? 15mm no good?

[chrisplumb]

I didnt know everything when I first started , and I probably dont now !But before I was let loose on my own in customers houses I worked under people who did know everything and were there to assist me , but I would have got a proper bXXXXXXXing if I didnt know how to gas rate an appliance and size the pipework correctly especially after just learning it all in college.

I have recently become Gas Safe Registered after doing a 10 week course, in which, they show you how to pipe size for appliances. Since I have been out on my own so to speak I always pipe size to how I was shown, this is the basics when fitting a new boiler, sounds a bit dodgy to me?
Why dont we have an area of the forum that we can use to discuss Gas related issues but you have to prove you are Gas Safe Registered to enter the forum via a valid engineer number?
If this alreadys exists please forgive my ignorance as i dont get on here to often!

 

[jonathanb]

Sorry Steve - I was just trying to give an example of max load scenario - combi boilers are often over sized purely for hot water requirements hence 40kw boilers providing 16l flow rates in 3 bed semis, with heating side only requiring a fraction of the output.Don't want more than 1 mbar drop over pipework thats for sure!

In America I believe gas is supplied up to 1 Bar to the meter - not sure what governed to after that?

With Chris on that - any tech info for reg installers only like ARGI, with only certain issues open to public. Only 10 weeks for your gas though mate!? - where you already in the trade / experienced and done your hours on appliances?

 

[Puddle]

I would like to bring up the reason why it is so important to correctly pipe size with today’s boilers
Since combination boilers hit the UK market it as always been required to take 22mm pipe work to within 1m of the boiler, this was to give the required heat output for the hot water
However if the gas pipe work was undersized because of the burner set up (normal atmospheric) as long as the boiler had the minimum gas pressure for it to operate the low flame it was safe ,all that would happen, is you would have tepid water or fill a bath in 2 hours if you wanted hot,
When the gas valve opened from low flame to give high flame the flame would increase to whatever maximum gas pressure was available giving you a lucky dip max water flow rate. The heating would work OK
As time went on boilers became more efficient and delivered better hot water with lower gas pressures/small pipe size to the point were most 24kw normal atmospheric burner boilers could deliver adequate hot water requirements (which suited a lot of builders, stick it on the wall, even comes with power flex, plug on end and away you go but I digress) again quite safe as long as gas pressure high enough to provide low flame all ok.
However now we are fitting a new kind of boiler, efficient and to achieve that efficiency we have a new burner lay out, the gas valve is not operated with modulating solenoids but by the fan speed. For low flame the fan runs slower giving lower pull on gas valve releasing less gas and for high flame the fan speed increases giving bigger pull on gas valve releasing more gas
This is why it is so important to have to correct gas pressures, because if not, the fan go’es to high speed and opens the gas valve fully and as the fan is designed to remove the burnt gases for a high flame at this point, if gas pressure/flow to low and only small flame available, the small flame will be pulled from the burner by the fan at high speed and extinguished or partly extinguished ,resulting in burner pulsating, incomplete computation causing unburt gas to be expelled through flue possible mini explosions in heat exchanger from unburnt gases and damage to the burner itself.
Of cause the safety devises on the boiler will kick in and put the boiler to lock out or into another circle but these devises are not there to be used in the normal operating boiler mode and the boiler should be able to operate normally without them
I have explained the above simply I hope, to explain why pipe sizing has now become a big issue, and why people have got away with undersizing in the past. It really is important to the safe running of the new era of appliance or infact the running of them at all that pipe sizes are correct.It is not just about gas blokes hitting the reg book

 

[jonathanb]

Nice report Puddle - to extend on that, although slightly off topic, Gas Safe operatives login to site and check out Technical Bulletin 13 re: air/gas ratio valves if you haven't already done so.

 

[chrisplumb]

Sorry Steve - I was just trying to give an example of max load scenario - combi boilers are often over sized purely for hot water requirements hence 40kw boilers providing 16l flow rates in 3 bed semis, with heating side only requiring a fraction of the output.Don't want more than 1 mbar drop over pipework thats for sure!

In America I believe gas is supplied up to 1 Bar to the meter - not sure what governed to after that?

With Chris on that - any tech info for reg installers only like ARGI, with only certain issues open to public. Only 10 weeks for your gas though mate!? - where you already in the trade / experienced and done your hours on appliances?

Yes mate, been doing gas for around 2 years until i gained enough experience/got off my fat lazy bum to do the 10 week course, could of & should of done it earlier really but all done know!

 

[jonathanb]

Sorry Chris - thought they were handing them out like sweets now! Congratulations & good see you doing things properly - good luck with things mate.

 

[BlakesHeaven]

Hello Corgi People,
I am a customer and I have a couple of options in front of me for a boiler replacement and this thread seems relevant, but I'm still missing an exact answer. Appologies if it is in the wrong place, maybe it can be moved by a nice moderator. I was just hoping that I might get an unbiased opinion as to which of the 2 options below would be best, i.e. do I need to have the house dug up to get a 22mm pipe to the boiler.

My current boiler is an old old Concord thing and has a 15mm input gas pipe. The house is a 2 1/2 bedroom, semi-detached (s-d) brick & tiled house with 4 large rads and 2 small rads. Water is stored in a tank. Small header tank is in loft. One slight complication is that there is an asbestos flu. The current supply comes in from the outside meter, runs within a concrete floor and somehow gets up to the boiler on the landing. I’m guessing that the run is something like; through outside wall for 2m, turn left, across kitchen for 1.5m to s-d divide wall, turn right, run 4m to centre of house with a T branch to gas oven/hob along this run, turn up towards landing for about 4m.

Option 1
Replace the boiler with a Halstead Eden VBX as it (apparently) takes a 15mm input thus negating the need for new 22mm piping. The company can not remove the old flu so have suggested it is located up in the loft. When I queried the header tank to boiler clearance being possibly to shallow the Halstead Eden SBX was suggested as it didn't need a header tank .

Option 2
Replace the boiler with a Wocester Greenstar 12Ri which will need 22mm piping plumed through the house . The company can remove the flu and thus site the boiler in the same location on the landing. Install 6 x 3m (22mm) pipe.

I think I’d prefer Option 1, but I’m concerned about the gas pressure (especially in winter) with the 15mm pipe and the water pressure with it being closer to the header tank. Any comments would be appreciated.

Thanks,
David

 

[Blackcatgas]

Hello Corgi People,
I am a customer and I have a couple of options in front of me for a boiler replacement and this thread seems relevant, but I'm still missing an exact answer. Appologies if it is in the wrong place, maybe it can be moved by a nice moderator. I was just hoping that I might get an unbiased opinion as to which of the 2 options below would be best, i.e. do I need to have the house dug up to get a 22mm pipe to the boiler.

My current boiler is an old old Concord thing and has a 15mm input gas pipe. The house is a 2 1/2 bedroom, semi-detached (s-d) brick & tiled house with 4 large rads and 2 small rads. Water is stored in a tank. Small header tank is in loft. One slight complication is that there is an asbestos flu. The current supply comes in from the outside meter, runs within a concrete floor and somehow gets up to the boiler on the landing. I’m guessing that the run is something like; through outside wall for 2m, turn left, across kitchen for 1.5m to s-d divide wall, turn right, run 4m to centre of house with a T branch to gas oven/hob along this run, turn up towards landing for about 4m.

Option 1
Replace the boiler with a Halstead Eden VBX as it (apparently) takes a 15mm input thus negating the need for new 22mm piping. The company can not remove the old flu so have suggested it is located up in the loft. When I queried the header tank to boiler clearance being possibly to shallow the Halstead Eden SBX was suggested as it didn't need a header tank .

Option 2
Replace the boiler with a Wocester Greenstar 12Ri which will need 22mm piping plumed through the house . The company can remove the flu and thus site the boiler in the same location on the landing. Install 6 x 3m (22mm) pipe.

I think I’d prefer Option 1, but I’m concerned about the gas pressure (especially in winter) with the 15mm pipe and the water pressure with it being closer to the header tank. Any comments would be appreciated.

Thanks,
David

Hi David, depending on the length of the pipe run the halstaed my still need to be at least part run in 22mm, the rgi will need to calculate the correct size etc of the pipe run to comply with the current regs.

 

[BlakesHeaven]

Hi David, depending on the length of the pipe run the halstaed my still need to be at least part run in 22mm, the rgi will need to calculate the correct size etc of the pipe run to comply with the current regs.

Thanks BlackCatGas. I have now measured up the run more acuratly as 14.1m with 10 x 90 degree bends and 1 T-Junction for the Gas Oven/Hob. Can you or anyone else recomend what option above I should go for.

Many thanks.

David

 

[moony]

Thanks BlackCatGas. I have now measured up the run more acuratly as 14.1m with 10 x 90 degree bends and 1 T-Junction for the Gas Oven/Hob. Can you or anyone else recomend what option above I should go for.

Many thanks.

David

without even looking what the gas rate would need i would say at least part of that would have to be 22mm due to amount of bends and length especially with a gas oven and hob coming off it.

go for the worcestor....

 

[Blackcatgas]

without even looking what the gas rate would need i would say at least part of that would have to be 22mm due to amount of bends and length especially with a gas oven and hob coming off it.

go for the worcestor....

I concur with q-plumb, its a bit late at night now to calculate it + Iam full of strong lager, either way, Halstead or worcester your going to need to uprate the gas pipe size, (cant this be run outside? etc) so you may aswell go for the worcester out of the 2 boilers.

 

[BlakesHeaven]

BlackCatGas / Q-Plumb, Thank you both very much. It is appreciated.

To answer your question, “cant this be run outside? Etc” – Unfortunately a run out side is almost impossible given that everything is on the side of the house next to the other half of the Semi-Detached. There is a possible run under the kitchen units and up a duct next to the soil pipe, but the oven is on the other side of the kitchen.

Just thinking aloud, I suppose the current pipe could be retained to supply the oven (& gas fire that I just remembered about) and break the new run off immediately after the meter. The only other option I can think of is to move the location of the boiler to the kitchen, but that would mean an equally long 14-15m run to the hot water tank, not to mention linking it into the radiator system.

Thanks again – I’ll most probably go with an upgrade to the pipe.

Cheers, David

 

[moony]

get a decent installer and he will calculate the easiest and cost effective solution, you may need 28mm and then 22, may come up outside drill through and run under floor boards and drop down to outlets. may find it easier that way - without seeing it i cant possibly say but any decent installer will let you know easiest and cheapest route.

 

[td1947]

I have seen these 22mm copper pipes appearing on the outside of relatively new houses. Personally I think it is an ugly way of doing it, but I suppose other methods are costly. My main reason for posting, is that PLUMBNUTS seems to be unhappy with DIY types asking questions on this forum. My undertanding is, that according to the LOGO on this site, that DIY questions ARE allowed,as well as from professional installers. The "going to prison" thing was mentioned twice, rather over the top I thought. My understanding is, that if a company, does unregistered GAS INSTALLATION work, AND CHARGES FOR IT, without being GAS SAFE REGISTERED, Is against the law. Perhaps someone can quote the law, that prevents someone installing their own boiler, then getting it checked/certified by a GAS SAFE registered person? TD

 

[newbie1]

in your own house you can do what you like BUT getting a gsr engineer to sign it off is not allowed as how can he possibly sign off something he hasnt installed and for what gain??? 50.00 notes in his pocket for leaving him liable for the whole install if theres a problem as in court the defence of
i didnt install it guv i just took a backhander to do the paperwork
its real simple if you want gas work done get a gas safe engineer

 

[kirkgas]

The pipe size depends on the Kw of the boiler, how far away the meter is, how many bends, other appliances on the same pipe. If the gas pipe inlet on the boiler is 22mm then 22mm pipe is required all the way.
If the boiler is running on 15mm pipe. Check the inlet pressure on the boiler when the boiler is working full bore and any other appliances on the same pipe are running.
The pressure should not drop more than 1mbar than the same test taken at the meter
Low inlet pressure can lead to incomplete combustion, a rise in carbon monoxide and any warranty from the boiler co. being void!
Best practice is to allow for the pipe size upgrade in your Quote

everything you have said is correct but i would add there is a distinct possibility of gas starvation to another appliance if you run a combi on 15mm pipe, eg cooker (which doesnt have FSD) is on and working, someone opens hot tap and combi fires up on full gas, depending on layout the cooker gets starved of gas and goes out, tap is shut boiler goes off and supply is reinstated to cooker which now has 3-4 rings passing full rate gas with no ignition

 

[td1947]

Well newbei1, I did not mention a backhander, OR £50. Are you saying that when GS engineers are asked for Landlord Safety certificates, the requestin LANDLORD ALWAYS knows the appliances have been professionally installed?? A landlord could have just bought several properties, and would not have personal, or even easily verifyable knowledge, about who installed what. I was talking about the GS CERT offered for about £40, on a legitimate basis. Is it not the duty or right, of any GS registered person, to report, via the GIUSP rules, the ID, AR, or NCS state of an installation?? I would have thought than these inspections potentially create MORE business, if a DIY'er does it badly. I beleive that some keen DIY'ers do the main install/plumbing grunt-work, but leave the actual gas connection and commissioning/testing to the proper GS registered person (a sensible thing to do I would have thought). In these economic times, would this sort of work be refused then?

 

[newbie1]

in a word yes
i am sick and tired of people who think its ok to do the work and then expect a gas engineer to pop in and sign the work off
i would not sign off any work i havent completed
doing a landlords cert and signing of an install are 2 completely different things
let me guess just a wild stab in the dark td1947 you are not a gas safe registered engineer
and if a diyer does it badly people can die and as such i dont want any tom dick or hary doing a bit of diy gas work no

 

[heatserve]

Halstead Eden *snigger*

 

[spudulike]

I'm looking for some advice and help - I have just had a combi boiler installed by a Gassafe registered fitter. All neat and tidy and it looks a good job.

But - the boiler is connected to the old 15mm pipe from the meter and is then taken up to 22mm for the last few inches at the boiler. Even though there was lots of discussion before starting the job about how to get under the floor and replace the pipes not a single floorboard was lifted. He is telling me that the pressure at the boiler is sufficient (although I do not think he has tested it with gas cooker and fire on at the same time.)

The boiler is about 5 metres from the meter in a straight line but the pipe is under the floor so probably has a few turns.

I am now worried that the boiler will underperform, be uneconomical and possible unsafe ?

Is the wider pipe a legal requirement ? Or if he proves that there is still adequate pressure even when all other appliances are running is the narrow pipe still okay ?

All advice appreciated.

 

[kirkgas]

safety is paramount, the MI's take the appliance requirments as paramount and might ask for 22mm pipe, if so easy peasy he is wrong, if the MI ask for a specific pressure then a test according to the gas regs and BS6891 needs to be carried out to determine what is required, if the pipe is wrong thew boiler under performing is the least of your worries more likely to create a prob at the fire or cooker, post the make and model of the boiler and also a distance/route as best you can for the 3 appliances

 

[Billy Bob Bob]

everything you have said is correct but i would add there is a distinct possibility of gas starvation to another appliance if you run a combi on 15mm pipe, eg cooker (which doesnt have FSD) is on and working, someone opens hot tap and combi fires up on full gas, depending on layout the cooker gets starved of gas and goes out, tap is shut boiler goes off and supply is reinstated to cooker which now has 3-4 rings passing full rate gas with no ignition

and this is exactly why we have pipe sizing,because this situation can and does happen

 

[spudulike]

safety is paramount, the MI's take the appliance requirments as paramount and might ask for 22mm pipe, if so easy peasy he is wrong, if the MI ask for a specific pressure then a test according to the gas regs and BS6891 needs to be carried out to determine what is required, if the pipe is wrong thew boiler under performing is the least of your worries more likely to create a prob at the fire or cooker, post the make and model of the boiler and also a distance/route as best you can for the 3 appliances

The boiler is a Worcester Bosch Greenstar 30Cdi combi. Distance from meter I guess at 5 metres. Gas hob is probably 3.5 metres. Gas fire is about 5 metres. These are straight line distances and as the pipes are all under the floor I don't know whether they have any turns.

The fitter is coming back to the house early next week - what should I be asking him to test or prove ? If he still insists this is a proper install can I get it checked independently somehow ?

Thanks for the advice - much appreciated.

 

[tamz]

A 30CDi requires 3.4 cubic metres of gas per hour to operate correctly. A 6m length of 15mm pipe (which is what you will have when adding in fittings) can only pass 1.9 cubic meters of gas so your boiler is working at just over half capacity at around 18kw.
The situation is made even worse as you have a fire and cooker and could lead to a situation as Kirk said where the other appliances are starved of gas.
Get him to do a gas rate of the boiler whereby you turn the boiler on to high rate (hold the chimney sweep button for about 10 secs) and time it at the meter.
Eg. A rough (but near enough) guide is
Metric meter (m3) time it for 2 minutes then multiply by 321 = kw
Imperial (ft3) 1092 divided by the time for 1 revolution of needle = kw.
You will need a 22mm pipe from meter to the boiler (22mm is stated in the manufactures instructions).

 

[fuzzy]

work out the gas requirement then you know!

wouldnt someone who had done their acs know this?

 

[spudulike]

A 30CDi requires 3.4 cubic metres of gas per hour to operate correctly. A 6m length of 15mm pipe (which is what you will have when adding in fittings) can only pass 1.9 cubic meters of gas so your boiler is working at just over half capacity at around 18kw.
The situation is made even worse as you have a fire and cooker and could lead to a situation as Kirk said where the other appliances are starved of gas.
Get him to do a gas rate of the boiler whereby you turn the boiler on to high rate (hold the chimney sweep button for about 10 secs) and time it at the meter.
Eg. A rough (but near enough) guide is
Metric meter (m3) time it for 2 minutes then multiply by 321 = kw
Imperial (ft3) 1092 divided by the time for 1 revolution of needle = kw.
You will need a 22mm pipe from meter to the boiler (22mm is stated in the manufactures instructions).

Tamz - Thanks for this and to other posters' replies. I'm now convinced he needs to upgrade the pipe. Are there any pipe sizing regulations I can quote to block any objections he might have ? Sure I've seen these in a previous thread but can't remember where.

The other thing I was thinking of doing, if he refuses to change the pipe, was to get an independent inspection done. Any ideas on how to do this ?

Thanks again

 

[oldplumber]

contact the gas safe register, let them know you are unhappy and having sought advice request them to carry out an inspection for you. If your really worried call in another fitter, checks his/her credentials so you know they are qualified and ask them to survey your sytem, youll have to pay them but youll get a simple report which if things are wrong you can refer to gas safe and trading standards and use to claim you money back from the original fitter if he fails to make good the work, which you must allow him to do if your to have a valid case if things dont work out in the end. have fun!

 

[spudulike]

Good advice - I'll give the fitter a chance to put it right first and then if no joy I'll call gassafe and see what they say. There is also a local plumber who I know is reputable and I'll get him to do a check.

At least I haven't paid yet .....

Thanks

 

[kirkgas]

Tamz - Thanks for this and to other posters' replies. I'm now convinced he needs to upgrade the pipe. Are there any pipe sizing regulations I can quote to block any objections he might have ? Sure I've seen these in a previous thread but can't remember where.

The other thing I was thinking of doing, if he refuses to change the pipe, was to get an independent inspection done. Any ideas on how to do this ?

Thanks again

BS6891 covers gas pipe supply requirements

 

[Eddie Charlton]

it should purley be down to what you calculate, taking the total kw usage at the address and the pipework layout to get from the meter to each appliance. dont take it for granted that the exisiting pipework was correct in the first place. the new boile might say that it will be acceptable to connect to 15mm, but that is only half the story. get someone in to survey the address to calculate the correct size pipe needed. it does not take long

 

[Bernie2]

All this confusion seems to back up a good reason why there should be a website with freely accessible gas work information for everybody.

We could then standardised the info and all work out of the same info.

The problem is the gas Regs are so uninformative and leave it open to interpretation as the forum shows. Some are quoting from manufacturers specs, some from British Standards and some from ACS or training courses. Its all a mess.

The likes of the Building Regs guides are straight forward and easy to get for free.

Why not do the same thing for gas work?

 

[Hoopey]

Have a look in the Manufacturers Instruction, newer worcesters and vailliants can work at 17mb inlet pressure there that economical. Tricky one though.

 

[tamz]

It has nothing to do with being economical. Most boilers will actually work ok at 17.
The point is that BS6891 states
"The pressure drop between the outlet of the meter and the points to be connected shall not exceed 1 mbar at maximum flow conditions"

 

[Assessor Gas]

Hi Tamz, I am a field assessor and inspector. Simply you need someone who knows what they are doing. It doesn't take 5 mins to size up pipework which is necessary on the majority of new installations these days due to the higher overall demand. Most people are missing the downside, and since i have inspected a lot of downsides, an undergassed boiler scales the Heat Exchange fins due to condensing in the combustion area. When the heat exchange blocks slowly you get vitiation and excess heat in there and then you get 2 problems. Incomplete combustion, and excess heat in the combustion area to burn through your seals. When checking G20 operating pressures you must run all the appliances not just one. Now check your pressure losses, and perhaps gas rate with all appliances on. From a safety point of view - well i thought that's what gas engineers training was for, and why the job prices are high. The customer's interests need to be in hand. For 10 years i have had to listen to "22 it will do" - Monkeys - If you got 15 in there even worse. funny enough just come from ispecting one today. Call Gas Safe, They want to hear from you !!!!! Good Luck