This calculator will give the Hydrostatic pressure at the bottom of the Heater Tank.
This is useful to know if you are using a on-demand hot water system, most of which require 0.2 bar to function.
The formula is P = pgh where;
P = pressure
p = is the density of the fluid (i.e. the practical density of fresh water is 1000 kg/m3)
g = the acceleration due to gravity (approx. 9.8 m/s2 on Earth's surface)
h = the height of the fluid column in meters.