Hi Christian,

Thanks for your reply.

On Tue, 02 Nov 2004 15:10:08 +0000, Christian McArdle wrote:

Q: Would I want direct or indirect? Direct seems simpler - pump the boiler
primary through the bulk of the tank and the rads.

It has significant advantages and disadvantages. The main advantage is that
it allows the boiler to reheat the store in a very efficient manner, dumping
its full load into the cylinder, rather than relying on an indirect coil
that might not be able to transfer as much heat.

That seems a clear choice then, for me (see below).

This is particularly useful
if you are running radiators off the store. It also allows the boiler to use
a lower flow temperature (good for condensing) as there is no need to
provide a temperature differential that a heat exchanger would require. You
can run the boiler at 75C, rather than 82-85C.

Longer life for the boiler...

The main disadvantage is that it doesn't allow sealed pressurised operation
of the boiler, a system which has a number of advantages, such as leak
detection and protection, pump over prevention, easier filling & flushing,
allowing radiators high up, etc.

Shouldn't be a problem. Only got rads on 2 floors, with the cylider on the
lower floor - I assume that will be OK?

So - from people that fitted thermal store cylinders: are they any good
and which one did you use? Any general theories/opinions also most welcome
:-)

I have a DPS Pandora heat bank (you refer to these as the "heatweb"). It is
an indirect type, as there are likely to be radiators as the highest point
in the system, so I wanted sealed pressurised operation. The rads are off
the boiler primary, not from the heat bank.

Ah yes - Heatweb stuck in my mind, but they do sell different things - yes
it was the Pandora.

I can't make up my mind whether to take the rads off the primary via a 3
way valve or use the heat store to feed them. I suppose that using the
heat store will guarantee long boiler burns. But is there a danger that
the radiators will deplete the heat from the store? Some pictures indicate
that the radiator feed is taken off the lower half of the cylinder, so I
presume not??

Was there any particular reason you fed the rads directly from the primary?

It is absolutely excellent and works entirely as described.
snip

Hmm - this idea sounds better than ever :-)

The biggest test was filling a 750 litre birthing pool to 40C. It managed
this in just over 40 minutes, although the outlet temperature did drop to
about the required 40C by the time it had completed.

Wow. I don't think that I've had a CH HW system that could run for 40 minutes
without going stone cold after 20.

BTW, I'd avoid the traditional thermal store type devices. I would only
choose a model with a plate heat exchanger for DHW operation.

Ah - I did see "heat plate" mentioned.

Thank you very much.

Timbo