If you only want 14 L/M flow rate then it is good enough, if you need more then it isn't. To give you an idea one good shower working will draw 12 L/M leaving just 2 L/M for anything else that may be on at the same time, not a lot is it.
20 might be better for you average house but it an't going to be any good for a 3 bathroom 6 bed place. See how it works ?
What type of fitting (taps) are you going to be using what flow rate do you need for them to work correctly, as before, what pressure do you have, how high is the cylinder / fitting going to be. Just a few of the things that need to be considered, it is not so easy this old plumbing lark is it.