22mm to combi boilers? 15mm no good?

[migoplumber]

plumbnuts, your right but calm down!

dan mekrl, manufactures instructions are to be followed over and above gas regulations, unless they contravene british standards. to contravene the standards the present instalation would have to fail them. our gas regs are not backdated which means his instalation under test might possibly be n.c.s
the british standards are never out of date, they are just ammended ( their rules not mine)

shaun

nor do i approve of unregistered/qualified people working on gas stuff they dont understand.
xx

 

[copperspropper]

Good practice to over size the guvoner and gas valve will work for you never under size

thats why the regs are there bruv always over size if any thing its good practice

 

[vdcplumbers]

Did you know that all condensing boiler love bigger size of gas pipes? 22mm ,but if the gas meter far away you need to re-size the gas pipes from 28mm to 22mm straight. then check the inlet gas pressure.I beat you if not enough gas supply You are in trouble... To be honest ask extra payment to your client and how ?and we need to be done. if doent agree,well, dont risk your Corgi I.D...if happen They will call a Corgi inspection or gas safety inspector to check the gas supply..Now You will recieve a letter to the Corgi..asking you to re-done or test....You must prove to them that is ok..if not..You will pay all the cost..Cover your pocket....I this days..Be clever..dont risk it..I learn this from my work for many times

Cheeers,
vdc

 

[jonathanb]

Sorry mate - "the dogs" went on the first of April!

End of the day if your installing modern HE boilers you should be working out your pipe sizes properly and charging for upgrading gas supply. A 40kw combi will work on 22mm but really you should be putting in 28mm, especially with consideration to other appliances -e.g. cooker ranges, what happens when both are in full use and boiler at max gas rate for hot water and the fires on in the living room also? A lot of these boilers will still work if minimum pressure there as self governing - but why turn a 40kw boiler into a 30kw by not doing your homework?

 

[stevetheplumber]

condensing or not makes no difference if you want 30kw of heat you need to burn enough gas to provide it to get enough gas you need a pipe size that will provide it at a given preasure
can anyone wiser than me explain why we deliver gas to our appliance at such low preasure if we had more preasure we could use much smaller piework

 

[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....