davidg wrote:Pipe inside a pipe. Some tanks have 2 inlets so it's not required then.
slightly OT.. but when I think of most tanks I have encountered, they have a plastic tube inserted into the COLD entry, that sends the entering cold to the bottom of the tank..
do you know just how the tubeINtube works??
You would normally want to send the returning HOT upwards, and suck the cold from the bottom..
I could only imagine that the device protrudes WELL into the tank , so as to ensure that you are sucking the cold, away from where the hot is returning..
and... with tanks that I have played with, it is very hard to remove the factory-fitted plastic tube..
I don't have a roof cavity so I'm not sure if solar is possible?
as per the last comment - we really don't have much to go on and so this is ALL pretty general..
Depending on what you mean by no-roof-cavity, SOLAR pipes could easily run above the roof..
returning to your main interest - INSTANT - do remember that there are INSTANT heaters that they install under the sink.. and plug into standard 10A circuits.. OBVIOUSLY, you will not get boiling water from that.. 2400W of power is about that of an electric jug.. you would end up with a low flow of warm water.. IMHO..
Assuming the power was available, you could think outside the box and cascade them (Possibly) to give a higher temperature..
You will likely see unapproved ones on EBAY and legal ones at BUNNINGS, and otherwise trade plumbing supplies..
GOOGLE should find some local products, and they would have to give details of performance..
PS - the thought comes to mind that IF you are creative, you could think about the tubular-heaters used in Front-Loader washing machines...