My elderly parents are in the process of buying a 1960s detached property. It would seem that very little has been changed since construction. As a result a complete rewire has to be undertaken together with a complete refurbishment of the kitchen and bathroom. Within this is the replacement of the boiler and hot water cylinder (gravity fed from tank in loft). Existing radiators to be retained. Mains pressure hot water would be preferred and therefore a thermal store (eg DPS Pandora) might be appropriate.

However, a number of issues have been raised and I wondered whether anyone here can help:

How much more expensive would a thermal store be compared with a replacement conventional or combination boiler?
How is a thermal store sized correctly?
Can a water softener be utilised (their's is a hard water area)?
DPS seems to have been used by a few members here, who else should we look at and does anyone have any words of wisdom?
Solar input is not likely to start with, but may be later on. Can suitable inputs be incorporated at installation without adversely affecting the system should solar not appear for a while?

I appreciate that a lot of this is probably quite basic stuff, although most plumbers seem to be rather bemused by the concepts, but all comments welcomed.

I've seen a 280 litre store for £880 + VAT. That's including a second coil to add solar at a later date.
I think an unvented tank wouldn't be much less. A standard insulated copper cylinder would only be around £200 though.
Or you can go bonkers as fit a 500l consolar for about £2000.

Hi,

Firstly a thermal store or heat bank provides mains pressure hot water without having the potable stored water held at mains pressure, this is what an “un-vented cylinder” does. An un-vented cylinder stores the hot water DHW at mains pressure. Consequently it falls under pressure regulations that require a safety valve, expansion vessel etc etc this must only be installed by a fitter with the necessary “ticket” (bit like corgi) and subsequently maintained by the ticketed engineer. A thermal store does not require this as the body of stored water is un-sealed; the potable DHW is only in the heat exchanger loop pipework so does not fall under the regulations. Because of this pressure they are usually glass lined steel or stainless steel and would cost anywhere from £500 to £1000 ish. Which is about the same as many thermal stores except they are usually in copper. Albion Mainsflow for just DHW is an example thermal store as an off the shelf item.
A thermal store is best for combining inputs as heating load is distributed from the central point. Another benefit is that if you are using oil fired which cannot easily be modulated down as temps rise, short cycling which is wasteful can occur. The thermal store presents a fixed volume load to the boiler which allows for much steadier running.

Cheers, Mike up North

The main benefit to a thermal store to me is that you can stick solar into the big tank and then use the stored heat either for domestic hot water OR space heating. So in the autumn and spring, you'll be able to use up all your solar generated heat, and then have the boiler kick in. It doesn't restrict you to using your solar water for showering, so you actually get to use more of it. It does mean however you may start getting tempted to up the size of you collectors and tank ;-)

If you go for unvented then the heating system will be on a split off from the main boiler flow circuit. The water in the tank is what goes to the taps. The coil that comes from the boiler split is on the same circuit as the rads.

In a store the tank water is shared between the rads, whilst the incoming fresh water goes through the coil.

The other key advantage as already mentioned, is that when you boiler does fire, it can keep going until the store temperature reaches say 80 degrees and then cuts out. This means that when the central heating is on, instead of firing say every 15 minutes, the store will buffer the heat and means it might fire only every 30-45 minutes. This is important as starting up and stopping a boiler is when it is least efficient. I'm guessing you need a decent programmer that's aware you have solar, so it doesn't fire the boiler at 5am on a summer morning, just as the sun is about to come out !

I should have checked my figures, it was £990+VAT but that' still good. It's for an Aqua-Sol store from a company called Underfloor Direct based in Northern Ireland. They were at the home building an renovating show, so it might be a special show price, but I'm sure you can twist their arm. Contact number is 028 9263 4068. info@underfloordirect.co.uk. Their website doesn't show it, but looking at the picture I have on the brochure I've found the same product here...

http://www.halosolar.com/products_cylinders.htm
http://www.rayotec.com/water_underfloor_heating/solar_linked_underfloor_heating/index.html

Simon

Wow ! life sure is complicated in the UK..
Here in France the usual arrangement is a sealed hot water cylinder, heated by off-peak electricity. Anyone with half a brain can fit them, they come as standard with a 'groupe de securitie' which is a combined cold fill, stop-cock, drain, and 3-bar pressure relief valve. Hang it on the wall, connect it up, and away you go. My 200 L unit cost under 200 Euros including a tripod for it to sit on.
Admittedly, once you start to add a CH coil the euros start to add up, but even so....

p

If you are still interested in the thermal store option then try Navitron - £790 inc. vat for a 210ltr store. I have gone for a store over an unvented cylinder because 1.I diddnt like the idea of so much high pressure hot water sitting around, 2. We had problems with a previous megaflow system - needing to renew the bubble every few months and 3. it was simpler and cheeper than an unvented version (circa £300 less for a 320ltr tank installed -solar version)

http://www.navitron.org.uk/e107_plugins/wrap/wrap.php?13