Generally if your control valve is 100% open you'll get around a 10 degree rise in water temp... example 43 deg inlet water 53 degrees outlet temp.
more than a 10 degree rise tells you you either have too few gpm water flow or your airside cfm is too high.... if you're getting less than a 10 degree rise in water temp..... too many gpm water flow or too few cfm airflow....
common problems are:
Air in the coil, plugged strainers, balance valves set incorrectly, control valve problems, dirty air filters, dirty coil fins, loose belts.
knowing the design GPM through the piping and design CFM on the airside is important.
Your airside temp drop depends on design but, can range between 15 to over 30 degrees drop
How can you have any pudding if you don't eat your meat?