chiefie:When we renovated our place, we took out the hot water cylinder and installed an outdoor hot water heat pump. It's great... We gained some space back inside the house, we don't use the main water reservoir in roof and we have hot water most the time.
What brand and model did you install? Have you had any problems with it? Do you run out of hot water sometimes? Nd if you do how long until hot again? Cheers