I was wondering when Tony would turn up 
Gas flow for replacement boiler
- Thread starter DaveMatt0709
- Start date
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Remember EACH 90 degree bend adds half a meter the effective length of the pipe. The longer that length the larger the pipe has to be.
God bless Tony and his random inputs
God bless Tony and his random inputs
Remember EACH 90 degree bend adds half a meter the effective length of the pipe. The longer that length the larger the pipe has to be.
God bless Tony and his random inputs
Yes got a phone call from Worcester-Bosch yesterday following a query I sent them. They told me to subtract 0.3 for every 90degree bend from the gas sizing calculation. He did a rough calculation over the phone for leaving the boiler in the cupboard and none are suitable, although 440CDi is the closest as pressure required is the lowest. Moving the boiler downstairs doesn't really help. Length reduces from 16.5m to 9m and no of bends from 6 to 3, the pressure would be 4.5 -0.3x3=4.6, which is just about OK for the 34CDi, but he told me this boiler would not meet our needs, confimring that we need the 38CDi at a minimum, but preferably the 42CDi or 440CDi.
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The quote says that this is the maximum we would pay, no hidden extras, but they do not mention the pipework at all in the detailed quote and have I have said there is no obvious or easy way to upgrade the piping. So if they haven't mentioned it, how can I trust if the pressure would ok and the boiler working as efficiently as it should if we went ahead with them? They also never mentioned the 5 year extended warranty for parts and labour from Worcester until end of June 2013. Instead said they would give us a year of servicing free. They also quoted an overly inflated price of £2000 for the 440CDi, which retails online for £1650. Total price for installation + boiler + wireless controller of £4700, with a discount of £550 for their sales giving £4150. Seems like a lot to me.
Dave, you dont seem to have understood what we have told you.
The boiler will work fine with an undersized gas supply.
However, the standards we have to work to require less than 1.0 mbar pressure loss in the pipe.
You can ask any quoter how they will achieve that and see what they say.
Tony
The boiler will work fine with an undersized gas supply.
However, the standards we have to work to require less than 1.0 mbar pressure loss in the pipe.
You can ask any quoter how they will achieve that and see what they say.
Tony
It's 0.3 for pulled bends. 0.5 for elbows.
Sorry Tony, yes I don't fully understand all of this, its true. To be fair the guy from Worcester did say no more than a 1mb drop from meter (usually 21mb) to gas valve then another 1.5mb drop is allowed to boiler giving total of 2.5mb. I will specifically ask this when I meet with the third installer later today.
Thanks for this, no idea what a pulled bend is though, he just said 90 degree bend to me was 0.3.
A machine bend. It's a bend formed with pipe benders, and has a set radius, not an elbow. Elbow adds 0.5m, formed bend adds 0.3m. The guy you spoke to at WB sounds like a numpty. Your gas pressure at the meter is required to be governed at 21 mb plus or minus 2mb. Straight away you could have 19 mb working pressure at the meter, and therefore with adequate pipework, 18 mb at the boiler.
Most manufacturers will NOT GUARANTEE the SAFE operation of their boilers unless you have the minimum working pressure at the appliance at full rate as specified in the installation instructions/manufacturers instructions. Some won't honour the warranty. More information on this minimum pressure can be obtained from the relevant technical helpline. Some allow a reduction in minimum working pressure due to pressure drop across the gas inlet cock.
Although a boiler may run perfectly well at it's full rate, albeit at a reduced working pressure, you must bear the other points in mind.
I have had this conversation many times with various technical help departments.
Most manufacturers will NOT GUARANTEE the SAFE operation of their boilers unless you have the minimum working pressure at the appliance at full rate as specified in the installation instructions/manufacturers instructions. Some won't honour the warranty. More information on this minimum pressure can be obtained from the relevant technical helpline. Some allow a reduction in minimum working pressure due to pressure drop across the gas inlet cock.
Although a boiler may run perfectly well at it's full rate, albeit at a reduced working pressure, you must bear the other points in mind.
I have had this conversation many times with various technical help departments.
What are your priorities? Hot water flow or heating? Have you checked the incoming flow of your cold mains? Not much point in having a whopping great boiler if your mains coming in is trickling at 12 litres per minute.
Thanks for this, it all makes sense and is what the second guy said when he came, although he hasn't measured the pressure at the meter or boiler. The third guy that came last night has now worried me, as I had to mention a potential issue with the pipes, when he looked he just said "that looks OK"!!! When I mentioned the length and number of probable bends he then finally said they would have to measure the pressure and probably upgrade the pipe. Then at the end I asked about the pressure relief pipe, he told me that these boilers have them internally and told me they were not required. What a load of rubbish, they are even mentioned in the installation manuals for these boilers. I argued with him but he was adamant. I can't believe how difficult it is to get someone who knows what they are talking about. That's 3 different installers and all 3 have given bad advice! I have come to the conclusion that we are going to have to install new 28mm piping on the outside wall of the house and take it through the wall and under our bedroom floor on a more direct route to the cupboard. Just need to find a gas safe installer who knows what they are doing!
Our priority is to ensure we get enough hot water. I do not know the flow rate of the rising mains except to say it is very high, we have the stop cock not fully open because of the high flow rate, this has been commented on before by plumbers and builders, so do not think we have any problem there.
Yes - FLOW, not pressure
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