In an earlier contribution to this discussion,
Blae wrote:

Hot water cylinder on a vented system 900mm high by 450mm diameter,
direct version. manufacturer advises capacity 117 Ltr.

Trying to work out if a pump installed via a flange to the tank and
giving say 12 Ltrs a minute at the shower. Assume 8 Ltrs per min is
hot water and the rest made up from the cold rising main.

What is the real capacity of useful hot water from such a cylinder. I
guess say 64 Ltrs so eight minutes shower at most.

Does this sound somewhat optimistic.

Eddie

I would have said it was better than that. I reckon that the actual water
capacity of the cylinder should be nearer to 130 litres - even allowing for
a raised bottom. Maybe the manufacturer's figure is for 'useable' capacity?
[I'm assuming that you're right about it being a *direct* cylinder - with no
heating coils inside.]

You shouldn't get too much mixing of the incoming cold water as it displaces
hot water out of the top - but you may need to adjust the hot/cold balance a
bit towards the end of the shower.

By using a flange which picks up its water (say) 200mm below the top of the
cylinder, you are reducing the effective capacity by about 22% - but you
should still have at least 100 litres available.
--
Cheers,
Set Square
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