We've currently got a hot water system with no hot water tank! It's a pain in the arse running a bath etc. Is it practical to add a tank after the rest of the system has been put in place? It's a pretty beefy boiler for the size of the house and it can cope with most demands.
I guess the water tank would have to sit in the loft, not a problem?
How we didn't spot this when viewing the house I have no idea, somebody should have said "hey, where's the airing cupboard!?" :-)
Yes, it is possible to add a hot water cylinder to a combi boiler. You will need to zone the heating circuit into CH and DHW parts. You should do this in a Honeywell S Plan arrangement, as this provides better future expansion and is much simpler to wire up, particularly if the combi requires volt free contacts for the room thermostat. Obviously, there are going to be issues with running pipes and siting the zone valves.
Consider the type of tank carefully. As it is going in the loft, and provided you have good mains pressure and flow, you should really install a system that supplies water at mains pressure. This good flow rates and doesn't need a bulky, heavy cold water tank above the level of the cylinder. The two main types are heat banks and unvented cylinders. A quick google groups on this newsgroup should come up with plenty of discussion on the merits of both.
You should probably divide the DHW side up. If the boiler is in the kitchen, it would be strongly recommended to take the kitchen hot tap off the combi and the bathroom(s) off the heat bank/unvented cylinder.
Christian.
I presume that you've got a combi boiler which provides hot water "on demand", and also heats the water for the central heating radiators.
On possible solution is to use the combi's hot water output for just (say) the kitchen sink and to split the CH side into two circuits - one for CH proper and the other for domestic hot water. This would require an indirect hot water cylinder and header tank plus appropriate zone valves and thermostats. Not impossible to retro-fit - but much easier if it's designed in from the start! Have you got a spare corner in which you could create an airing cupboard? It is more usual to locate the hot water cylinder on the first floor rather than in the attic - but the header tank could be in the attic.
OTOH a conventional tank in attic + hot water cylinder in airing cupboard system (possibly with both in the attic if space etc allows) will be cheaper on materials and it may be easier to find an installer familiar with and qualified* to install such a system (and you may therefore be able to get the work done more cheaply, if you're not, as it sounds, proposing to DIY). You'd then use the tank+cylinder system for baths and general hot water supplies and use the combi for showers.
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