Small family or stay home alone doesn't need a wholehouse tankless water heater. You can get a single or multi-point heater that can provide good amount of hot water in minutes.
Of course, if you want you can get that type. But in cost efficiency point of view the tankless water heater like that is wasting more of your money. First, they need huge power to run that can lead you to add more fuel inside it. And maintenance cost is a bit higher than single point. To get the best of it, you can click here or you should consider your daily usage volume and calculate it with products that available in the market.