Horizontal vs Vertical Geyser Mounting
The majority of domestic geysers are installed in South African households are installed horizontally. This is because 'it has always been that way' and South African lofts are low pitch limiting the space for a vertical installation. Geysers are commonly installed in the loft and by placing support beams across the roof trusses, a simple base can be constructed for the geyser and drip tray.
This is not the most efficient use of the geyser and by installing the geyser vertically, the user will be able to use the geyser in a much more cost effective way over its life-span.
This is due to STRATIFICATION.
Water stratification occurs when water masses with different properties - salinity, oxygenation, density, temperature - form layers that act as barriers to water mixing. These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers. – Wikipedia
Hot water is less dense than cold water and so, in a geyser the hot water sits in layers with the hottest water being at the top of the geyser.
Geysers installed in vertical configurations have much better stratification, and maintain this stratification better than equivalent sized horizontal geysers. Fig 1’s stratification surface area is much smaller than that of Fig 2’s, creating a smaller surface area for conduction between layers and less turbulence disrupting the layers when water is run through the geyser.
Some geysers are not able to be mounted vertically but if you are replacing a geyser or having one installed as part of a new project. Investigate options for installing it vertically.