Minimum size of cold water tank?

One of my jobs this summer is to replace the loft tanks and the supporting woodwork, since it has sagged so much that it is almost touching the plasterboard.
Screwfix sell standard cold water tanks in 25g and 50g capacities. I'd prefer a 25g since it's easier to handle. Are there any regulations which state what capacity it has to be?
jim
--
Jim Hatfield

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The limiting factor is usually how much water you want to draw from the tank at any one time. If your bath is fed from the cistern, it also tops up the hot water cylinder and you like a deep bath, you may find that 25 galls means that the water slows to a trickle part way through filling. If your hot water comes from a flow boiler and the cold water is all mains fed, the cistern is only acting as a reserve for your WC cisterns and 25 galls will be fine. Personally, I fitted two 25 gallon cisterns, linked at low level (about 50mm off the bottom) with a large bore pipe, with cold water drawn from that pipe. That was partly to spread the load more widely around the loft and partly because of the size of the trapdoor.
Colin Bignell
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If you have any gravity fed showers, now's the time to build a trestle and increase the head pressure to them (raise the store tanks as high as is reasonable). Don't be tempted to insulate below the new tanks though!
Phil
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tank
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In last house I replaced split large round tank with two 25g tanks connected by two 28mm pipes at bottom. These were chosen as easy to get though the limited loft hatch size without having to fold, bend, squeeze etc leading to possible future damage.
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On Thu, 1 Jul 2004 14:50:59 +0100, "nightjar"

Hmm, well I never use the bath, there's a pumped shower, but I guess I should think about the future owners of the house!
jim
--
Jim Hatfield

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I thought the advice was to ensure a "flow" of water from entry into the tank to exiting from the tank. Presuming only one ballcock, your setup might lead to areas of still water which might encourage stagnation?
Just mentioning the point.
Mungo :-)
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wrote in message

drawn
Running a full bath, which I like, virtually empties both (I have a large bath) so most of the water changes daily. The only problem I do get is that the fill is less positive since fitting the second tank, so sometimes the ballcock starts a bit of water hammer. I can relieve that by opening one of the cold taps attached to the mains, but permanently correcting it is on the to do list.
Colin Bignell
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Hmmm... I'm not convinced Colin: If your daily consumption of water is more than the capacity of the tank, can you also ensure that you use all of the "old" water before any of the "new"?

When I replaced my cold water tank a few years ago I took the advice mentioned here and fitted a "Torbeck" valve. About a year ago I got persistent water hammer. A swift email to the company and they sent me some new components for the valve - methinks there was a design problem with the original. So if your problem is via a Torbeck valve then consider this.
Regards
Mungo
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