I'm having a central heating boiler replaced to a Baxi condensing one but my
installer called this morning to tell me that the Baxi he was going to
install has been discontinued (Baxi 80 HE Plus) and a newer model will now
be installed that doesn't require the gas supply pipe to be 22mm. The boiler
he said will now be installed is a Baxi Duoheat ( I think that's what it was
called) with a built in filling loop. I have been on the Baxi website but
cannot find that boiler. What I want to know is has anyone else heard of
that boiler and is it right that it doesn't need a 22mm supply?
When I did the calcs for my own installation with a boiler of similar size
15mm was a no-no by a long way. Like you I couldn't see a Duo-tec 24HE
but the installation manual for the Platinum 24HE shows a 22mm inlet pipe
and the standard minimum inlet pressure of 20mbar. Note also that having
a 15mm inlet pipe on a boiler is no indication that a run of 15mm is
adequate, my own is 15mm but is increased to 22mm within a foot of the
case to avoid excessive pressure drop on the pipe run.
If you can get a look at the installer manual look for the Gas Inlet pressure
quoted in the Specification section, if it's the standard 20mbar then I'd
suggest that 15mm is a no-no.
The size of pipe required will depend on the distance from the meter to the
boiler and any bends or other off-takes along that route.
I don't know the formula but you'd need around 22mm pipework for boiler
providing 30kW at up to 30m overall.
I think15mm could only be used for something like 10m overall.
To determine the overall/effective length, you need to add about half a
meter for each bend along the way. I've no idea what effect a tee off to a
fire or gas cooker would have, but I'd assume another meter.
You've got to allow enough gas to flow to the boiler. The more heat the more
gas is required, otherwise the boiler will be starved of gas and not reach
full potential (and may not even work at all).
I'd expect all boilers to require 22m pipework (or larger). It doesn't need
to be that size throughout, so long as the required flow rate at the boiler
can be achieved.
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