My daughter is getting in some quotes for a new boiler in her flat: a Worcester-Bosch 24i combi rather than the present Ideal(?) sealed cylinder system.
Latest to quote has said that the 22mm gas supply needs to be replaced by 28mm. None of the others have mentioned this.
There's around 16M of pipe and 10 or 12 elbows between the meter and the boiler. Does the need to increase from 22mm to 28mm sound plausible?
If it does, does it need to be the full 16M?
TIA
yes, see
ball park, pretty much so, but do your own calculation
Jim A
Thanks: just what I wanted.
It looks like the effective pipe length is 22.5M and the boiler + gas fire will need 3.1M3/hr. At that rate the maximum run of 22mm is ~18.5M.
I'm stuck for how to calculate how much of the 22mm would need to be replaced by 28mm to get the required flow.
Is it a simple ratio? At 15M 28mm delivers 7.0M3 while 22mm delivers the
3.4 needed, ie roughly 2:1. So, on that basis, should 1/3 of the run be 28mm and 2/3 22mm?Any help gratefully received!
Doubt its a simple ratio because the the first pipework section will carry fire+cooker+boiler and so there will be more allowable pressure drop in that section. As a guide, taken from my spreadsheet calculation, no guarantees although it worked out OK in practice, for a 28kW boiler, fire and cooker,
50% of the allowable pressure drop occurs in the first effective 4.5m of 22mm compared with effective 11.1m of 28mm. Not what your gut feeling is though I stand to be corrected.Jim A
It's best to turn the calculation upside down and work out pressure drop per metre for both 22mm and 28mm pipe at your required flow rate. You can then work out the total drop for various combinations, and find one which keeps you within the required 1mB.
Agreed. It's quite difficult to install truly compliant pipework. See BS 6891 linked below. Inspection and monitoring although not frequent has real teeth.
There is also a method shown in BS 6891 (linked below) where by each segment is allowed a proportion of the 1mbar pipe work loss.
No.
Boilers should have their own dedicated supply back to the meter.
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