vertical hot water cylinder laid down

[StudWall]

i noticed today that my current cylinder is rather big and that much smaller ones are available (900 x 450)

if i were to get one of these smaller ones and the top of that was below the bottom of the cold tank, would that matter??

 

[StudWall]

i noticed today that my current cylinder is rather big and that much smaller ones are available (900 x 450)

if i were to get one of these smaller ones and the top of that was below the bottom of the cold tank, would that matter??

can anyone help with this?

also considering a horizontal tank but wondering how much height i would need between the cold feed tank and the hot cylinder.

any advice appreciated