Thanks for all the info.

Andy Hall wrote:
- If you are thinking about any form of direct mains fed hot water,
then measuring the cold water rate at the cold tap in the kitchen is
very important. If the supply is less than about 20 litres/min, you
will be quite disappointed by the results in comparison with the
existing storage system in terms of time to fill the bath. With two
small kids, this will matter increasingly.

Dumb question, but is measuring the water rate as simple as timing the
time it takes to fill a known volume, then extraploting?

Nevertheless, with the caveats, this might be a good choice. Have you
thought about siting it in the airing cupboard instead of the
cylinder? Is recovering the cylinder space important?

Yes, at present, the boiler and the hot water tank are in our smallest
bedroom. We don't really want to place them in another bedroom and we
don't have anywhere else we can put it. Unless we go for the loft but we
have no brick wall in our loft, so that would increase expense we believe.

thanks, dan