Ok, now the tit for that is over, IMO even though manufacturers make high volume/high recovery cylinders be it tank in tank or indirect coil, the reheat of these is going to be extremely large in relation to heat input.
If your only going to shower at set periods and they'll only be used once then the length of reheat isn't that important but it should still be done within 1hour.
Hot water priority is a realistic solution in a domestic sense other wise you well could be adding another 20/30kw to your boiler size if the hot water and heating run together with a fully depleted store.
I'd seriously have a look at rinnai with a buffer before leaping in with any cylinder, trouble with any gas fired heater is the gas supply, if your on a domestic u6, your very likely to have no chance in hell, unless you adopt something like the rinnai twinflow and use a flow switch on the water heater to disable any other gas fired appliance.
Accumalators IMO are crap, you need double the size for useable volume ie 300litre ACC will give 150litres of improvement as a rough guide.
It probably won't help you achieve 80lpm (4 showers hot and cold).
That's where my 1100litres came in 500cylinder plus 600ish ACC. Would probably need more than that if you like a good long shower.
Yes ACC are quiet and have no electrical/mechanical parts...until recently lots of cylinder manufacturers wouldn't allow one to be used with there cylinders, GAH had some patent crap going on.
Pump sets will do your job without having to even think, down side is obviously a water store and that its a pump which aren't the quietest of things and can/and do breakdown.
