Gas sizing chart

[buckley plumb]

been to look at a gas pipe job today and the boiler will be 9m away from the meter and there is a fire and a hob .so when calculating the gas pipe the boiler lenght with elbows etc equals a lenght of 15m and there are 3 sections of pipe so the 15m must be multiplied by3 to give a max 1/4 pressure drop so pipe lenght equals 45m.the charts in corgi and viper books only go to 30m pipe lengths -where can i get charts for longer runs also the charts only go up to 28mm .

thanks ant

 

[newbie1]

are you sure you have done ur calc correct

 

[Gray0689]

Yes try again

 

[gbgas001]

Hi Ant

Your missing the key info of the appliance(s) gas rate and how your putting the info into the chart.

the information inside the chart with the pipe lengths along the top and the pipe diameters down the left, is the size of the appliance (gas rate m3/hr) with a one MB drop from inlet to oulet.

The gas essentials book shows you how to do step by step or download
http://www.gb-gas.co.uk/gb-gas%20QuickReferenceGuide2010v2.pdf

and have a look at page 29, walks you through step by step. or if you have excel on you computer you could use the spreadsheet calculator
http://www.gb-gas.co.uk/page_20.html

Hope this helps
gb-gas

 

[buckley plumb]

hi thanks but i know how to do the calcs just the charts i have only go up to 30 m in lenght. was wondering where to obtain charts for longer runs above 30m.
above links are great why cant acs and gas safe make their info so easy this is a great aid


thanks ant

 

[gbgas001]

Its because the British Standards BS 6891 only supply tables up to 30m.

have a look at this webcast its only 11 mins long but very good
Domestic Gas Pipework - Pipe Sizing

 

[buckley plumb]

thanks for that info its very good . i have been using the method in the corgi book and viper book to do my gas sizing,which is total different and looking at both methods now not the most acurate.The method on the link looks a lot better


thanks ant

 

[Toddyplumb]

Ant , can you explain why you think its 45metres

 

[gbgas001]

The Corgi book and Viper book use the same method as the video... the video makes it easier to understand.

Gb-gas

 

[buckley plumb]

yes mate in the corgi book, say you have 3 appliances and there are 3 pipe legs to some appliances then say the boiler and other apliances = 30kw giving approx 3m3/hr gas and the length including fitings is 15meters for first section of pipe the book states each section should be multiplied by the max legs eg 3 to give a 1/3 max press drop eg 15m x 3 =45mequivalent lenght and read off chart the lenght and and pipe size the problem being the chart only goes to 30m .if there were 5 pipe legs to an appliance then the lengths would be multiplied by 5 to get 1/5 max drop.the corgi book and viper is an easier way to do it but i think an over kill.its in the corgi essential book.an example can also be seen on the worcester bosch web site showing the above method.check it out and let me know what you think.i have been using this method for ages but normaly the calculated lengths are not normaly over 30m.

thanks ant

 

[bikerbas]

Try the link provided its a lot easy to work out.
45m seems a lot of pipework and elbows
http://www.ukcopperboard.co.uk/lite...ion-Tips/Domestic-gas-planning-and-sizing.pdf

 

[Toddyplumb]

Ive never done it that way . I just use my old CITB way gas rate then calc length / max length to give actual pressure loss in each section .
So for your 3m3 over 15 metres 22mm copper gives 1 mbar calculated drop No good ( Debatable ? NO ) so 28 mm gives less than 0.5mbar (using max charted length of 30m)
You obviously need your flow chart for this Hope you understand it

 

[GPSNewcastle]

I dont understand the way you have gone about calculating this, mainly because of the reference to "3 legs", as far as I know the calculation is from the meter to the appliance with an allowance for fittings and a max drop of 1mbar from meter to appliance. If the length from the meter to the appliance is about 9m I dont understand how you have come to 45m

 

[Toddyplumb]

I had never seen it either but it is in the CORGI book like that . I had a look last night . I suppose its like all these things its horses for courses as to the method you use .
But with my method you dont need to find 45metres !

 

[GPSNewcastle]

Same here...and I dont have a problem with gas rates! I think anyone using this method will be oversizing pipework and crippling their margins! Haha

 

[buckley plumb]

im changing to the other method. well at least i know if my customers want to upgrade in the future they should be ok lol.

thanks for the advise ant