In an earlier contribution to this discussion,
Russ wrote:

"direct" as in it's got an immersion heater only

"indirect" being the tanks with the additional connections on the side
and the coil inside, into which you'd feed water from the boiler.

All we've got is immersion heated water.

In that case, the terms "direct" and "indirect" don't have any relevance to
your situation. They both apply to situations where the water is heated by
an external source rather than by an internal immersion heater.

With a direct cylinder - often used with back boilers behind coal fires -
the water which circulates between the boiler and the cylinder is the *same*
water as comes out of your hot taps. With an indirect cylinder, there is an
internal coil/heat exchanger through which water from the boiler circulates,
heating the water in the cylinder *indirectly* without mixing with it.

If you use an indirect cylinder, you will simply have an unused heater
exchanger sitting inside it - it matters not one jot. In fact, it will
provide a modicum of future-proofing in case you ever want to convert to an
external water heating system.
--
Cheers,
Set Square
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