CraigB wrote:

The current Baxi system is coupled with a large (4/5ft tall ?) Heatrae
Sadia Megaflo cylinder and the hot water system is mains pressure. I
know next to nothing about how the Megaflo system works, which may
explain my next question...

Mains pressure hot water cylinder basically.

My friend has suggested (by phone) a Worcester-Bosch 40Cdi boiler,
which has lots of interesting stats. such as a 16l flow rate. Googling
has also found the Worcester-Bosch Highflow 440 with a 20l flow rate

The highflow is to all intents a purposes a large box containing the
components you already have. So probably not much point in changing to
that.

right in assuming that the Megaflo cylinder would mean that the 40Cdi
could meet my requirements as well as the 440 could ? He's also

Yup, probably better.

offering me mates rates utilising his trade discount to get the 40CDi
for circa 940+VAT...which seems better than anything google has found.

You don't really need a combi in this situation since your total flow
rate from both the cylinder and the combi would still be limited to
whatever your cold main can deliver. What is more, if you were drawing
water from the combi side, then boiler would not be able to reheat the
cylinder while you are doing it.

Hence a powerful boiler that can when required throw all its effort into
heating the cylinder would probably work better.

You need to measure the flow rate you can get from the cold main
however, as this is going to limit what you can expect to achive[1]. How
much flow you need will also depend on your expectations regarding
shower performance (4 lpm would equate to a crappy electric shower, 7 -
15 lpm would be a average mixer shower, anything up to 30 lpm if you
want showers with drencher heads and body jets etc).

[1] If you run out of flow rate capability, then you would have a few
options ranging from upgrading your cold main, installing an accumulator
to provide a buffer of mains water, or adding a conventional storage
system for filling baths and/or a pump for the showers etc.


--
Cheers,

John.

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