I just want to find out how many minutes of hot water should I have and how long it should take for the water to get hot once it has been used up if I have a water heater that holds 19.9 gals.?
Is it gas or electric? In either case, a 20 gallon water heater is not going to give you a very long shower even with a flow restricting head. The reheating speed depends on whether it is gas or electric and the input rating.