How to measure gas-pipework capacity

[manwithoutvan]

Hello

My old 24kW Glow-Worm-Swiftflow-80-S-I-T boiler has packed it in and I am am considering installing a new Worscter-Bosh boiler.

My plumber says that he cannot tell if the existing pipework will support a given size boiler without first buying and fitting the boiler due to some of the existing pipework being hidden under floorboards. This seems odd to me and so I have a couple of questions for you. I would not like to purchase and install a new state-of-the-art combi-convection boiler only to find that I then have to completely re-do my gas pipes at considerable cost and damage to by newly laid floors.

My question is

Is there a measurement that the plumber can make at the point where the existing defunct boiler sits (or elsewhere) to determine what size boiler can be supported without changing the existing pipework?

My shortlist for the new boiler consists of 25SI, 25Junior and 27CDI all from the Worcester-bosh range.

Any ideas?

 

[Stamina]

you mean just the gas pipe work?

 

[morlomanc]

your rgi should be able to take readings of working pressures at the meter and appliance to determine what he needs to do.

 

[Bankrupt]

Your rgi should be able to take readings of working pressures at the meter and appliance to determine what he needs to do.

Yes - but if there's a hidden restriction between the meter and the appliance the working pressure at the appliance could decrease dramatically once any new appliance starts consuming gas.......

Bear in mind he's said that his current boiler has packed in.

 

[gigz]

He needs to know the length (including bends) and diameter of the gas pipe back to the meter, and other appliances, if he cant see whats already under the floor then he can only chance it, i recently fitted a boiler (old one was piped up in 22mm copper) and when i did the tests found that the previous gasfitter had connected onto 15mm under the floor (new laminate throughout) it all had to come up.

 

[morlomanc]

well true...... of course working pressure with all the other gas appliances running! mmm missed the bit where he said the boiler had packed up!

 

[manwithoutvan]

Hi

Thanks for the feedback.

I would have thought there would be some sort of instrument that could be attached at the old defective boilers gas inlet which could measure how much gas can be sucked out safely. The max gas consumption rate for the new boilers can be found in the suppliers product literature.

Or am i missing something..

 

[namsag]

Your missing something..
A gauge can be used on old appliance but this will only measure standing pressure which is completly different from working pressure and wont let him know if its within limits of permitted presssure drop along the pipework.

 

[manwithoutvan]

Sure but is the static gauge the only instrument in the corgi certified plumbers toolbox?

 

[namsag]

Yes it is

 

[Bankrupt]

Sure but is the static gauge the only instrument in the corgi certified plumbers toolbox?

What you'd need is an arrangement with a flowmeter through which you could vent off to atmosphere ( make that flare off to atmosphere for safety reasons ) measured amounts of gas and a pressure gauge to see what working pressure that left you with.....

I'm not aware of such a piece of equipment - Should I invent one and go on Dragons Den ? ! . Personally, rather than have any doubts, I'd just pipe from the meter to the boiler in 22mm pipe - That should give you plenty of capacity. Combi boiler consume a lot of gas when you're running a hot bath for example.

 

[manwithoutvan]

Thanks! That makes sense.

Yesterday I contacted the manufacturer (Worcester) and the technical support person said that a "gas pressure drop test" can be used and that the instrument to measure this is available to corgi plumbers. Do you agree with this or will this test not give the necessary accuracy?

 

[Bankrupt]

The problem is that without a device like I've described you can only do a supply line pressure drop test when the appliance is actually installed and consuming gas - preferably at maximum consumption. ( The pressure drop test measures the working pressure at the appliance location versus the gas flow rate. No flow = No pressure drop. The higher the gas flow rate the bigger the pressure drop and consequently the lower the working pressue at the appliance)

If you then find that the pressure drop is too much ( i.e. at high gas consumption rates the working pressure at the appliance is too low ) it's a bit late - You've then got to re-pipe from the meter to the appliance in a larger diameter pipe. I though the issue was that you wanted to know whether your existing pipework had enough flow capacity or not before you decided on a new boiler ?

I've got a Worcester Bosch 28CDi in my own house. It's about 5 metres from the meter. When I installed it I had to change the gas supply line to 22mm. If you look online for the manuals for the boilers you're considering they should state what supply pipe diameter they recommend. .

 

[Agile]

The people who answer phones at manufacturers are not normally qualified and working gas engineers! They read out manufacturers data and know about common faults.

As has been pointed out the only way to measure pipe resistance is to flow gas through it!

We are not permitted to vent larger amounts of gas to the atmosphere for safety reasons and even if we did that the smell would cause lots of people to phone to report a gas leak!

In theory one would be able to burn the gas off but that procedure is not available for domestic size installations.

If it was my job then I would be able to estimate the pressure loss but that facility is not available to the average installer.

The correct solution is to choose your prefered boiler and accept that yo may have to pay perhaps £200-£300 to have the gas suppply upgraded. On many properties that can be fitted on the outside.

Tony

 

[Bankrupt]

Sound advice Tony

I particularly agree with you on this :

The people who answer phones at manufacturers are not normally qualified and working gas engineers! They read out manufacturers data and know about common faults.

People who have been to the Worcester Bosch HQ tell me that the a lot of the Technical Assistance people look like Page 3 girls ! . Given the level of "advice" I was given when I rang them once I can well believe that ! .