Our current tank is an old 22 gal. (100 litre, ish) one and after fitting
a new bath which is a shade bigger than the old one, is only just enough
to fill it hot, so this years project is to fit a new tank. (One of this
years projects, oh will it ever end!!!)

Current way to heat it is from conventional back boiler (non condnesing
with hopefully a good few years left in it yet) on a standard Y-Plan
system with a 3-way valve feeding the tank and CH loop (5 rads, but I
want to add 1 or 2 more). The tank coil for this heater is a "top-loader"
presumably replacing an old immersion heater. (system fitted by previous
owners) There is also a range cooker (Stanley DWH) with a back boiler
feeding a conventional coil in the tank. The top-loading coil doesn't
seem too efficient to me - the boiler cycles a bit quicker than I'd
like when trying to heat the tank up, and it takes a long time to get
the whole tank really hot...

So rather than just fit a conventional (2 coil) tank, I'm thinking of
moving to a heat bank/thermal store system and after enquiring, realise
I can't really afford a DPS/Pandora system, (was quoted close to £1500)
so wondering about DIYing it...

I'm not a fan of pressurised systems - it's true that I do a lot of SCUBA
diving where I encounter tank pressures of over 250 bar, but I try to
avoid it if I can... So, the idea is to start with a big well-insulated
coil-less tank with loft F&E tank. I'd love to put the tank in the loft,
but the hatch isn't big enough )-:

Bathroom Hot & Cold will be fed from tanks in the loft (via existing
Stuart Turner pump), kitchen will be gravity fed (as it is currently -
HW tank is on same floor as bathroom, loft is one up, kitchen one down)
- mains pressure is high where I am (8 bar!) but flow rate is low and
that won't be fixed unless I dig up a lot of tarmac/concrete to see
where the restriction is)

The tank will be directly heated from the existing conventional back boiler
assisted by the cooker with small back boiler and eventually supplementary
heated from roof-top solar panels.

So Q1: Can I just parallel up the heat sources like this, and just tap
into the top and bottom of the tank round its periphery with 3 inlet &
outlet pipes to the various heat generators? Each one will be pumped
(Although the cooker right now is gravity fed)

(I've heard the words "Dunsley Neutraliser" banded about, to combine
heat sources like this, but as I understand it, a thermal store will
just act like a big DN...?)

Would there be a problem with the cooker, back boiler, central heating
system (and solar) all sharing the same water and F&E tank? (The down
side is having to drain the lot if there's a problem, but with isolation
valves in the right places, I think I can live with that)

Q2 is how to get the heat out - A plate heat exchanger would seem to be
the most efficient - can these be bought independently of a tank and
DIY installed? A pump on the tank side and a flow-switch on the other
side is all I need, presumably.

They seem to have diffusers on the inlet & exit inside the tank (going
to the heat exchanger) - does the tank have to come with these fitted,
or are they just sections of pipe with holes drilled horizontally?

The only other conundrum is how to heat the radiators... Do I tap off
the tank with another pump, (+TRVs, thermostats, timers, etc.) or use
a conventional Y-plan system off the back boiler?

This system will have more pumps that I can shake a vacuum tube at,
and the tank end up looking like a colander!!!

I suspect the major cost is the plate heat exchanger and control
units. (And maybe the tank, and dozen essex flanges I'll need to plumb
into it!) Basically if I can save £500 on the bits, I'd put it towards
the solar panels. (Although fitting them will require scaffolding, to
bridge over a lower glass roof, so it might work out to be even less
attractive, but thats another problem for another day ...

I guess the only issue with a non-pressurised system like this is that
the F&E tank will have to be above the solar panels, but I can worry
about that later...

And any ideas where the best online places I can use to get the basic
parts? Essentially tank and heat exchanger...

Thoughts/comments welcome!

(Eg. how many building regs I'll be breaking!!!)

Thanks,

Gordon