On Thu, 01 Jun 2006 20:38:36 +0100, thescullster wrote:

Hi all

Looking at a replacement central heating/HW boiler and reckon I will need
something like W/Bosch 24Ri. This states a requirement of 2.67cu.m/hr of
gas.

I have a 22mm gas pipe running right across the house to the location of the
current boiler.
Assessment of length and addition of effective length for bends etc gives
23m equivalent length of pipe.
From R D Treloar, this looks to be right on the limit for 22mm dia pipe.

Also we have a gas fire tapped off this main (approx 4 m from gas meter).
This is an occasional use decorative affair claiming 6.5Kw gross heat input
required.

Does anyone know enough to comment on the viability of this install?
What would the effect be if the boiler were running and the fire turned on?

As we have concrete floors throughout and the boiler location is as far from
the meter as geographically possible, what are the alternatives (please
don't suggest moving)?

Also I note that previously it would have been likely that this main would
serve:
Valor Homeflame gas fire
Landing gas heater
Gas cooker
CH boiler 50,000 Btu

Surely this lot would put as much if not more load on the supply?
Final question - if the gas supply pressure as measured is high, can I take
this into account in calculation? I believe 20mBar is the datum pressure on
which these figures are based?


By the book it usually possible to correctly design the pipework. In
practice the pipework in _most_ houses and flats (that I come across)
drops more than 1 mBar between meter and appliances.

The installer can't usually take the risk to reuse undersized (but
functional) pipework because the monitoring and inspection
process has real teeth.

By the book the meter supplies gas at 19-23 (used to be 20-22) mbar.
The pipework should take no more than 1 mbar so leaving 18mbar + at the
appliances.

The W/B will insist on 18mbar minimum inlet working pressure in the manual.
IIRC this is a forced premix burner so will not readily tolerate poor
inlet pressures.

In practice the meter will almost certainly be giving 22 to 20 mbar at the
outlet depending on the rate of gas flow. This means that you will almost
certainly get your 18 mbar even with the fire on at the boiler. So you
have a functional but irregular installation just almost like everyone
else.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards