How much longer does it take to get hot water with the Navien tankless waterheater?
How much longer does it take to get hot water from a tankless heater than from a tank heater?
Because the Navien NR-240A has a small reservoir of hot water (think of it as a very small tank heater), if you require a small amount of hot water e.g. to wash your hands, the amount of time to get the hot water is the same as you'd wait for from a tank heater. However, if you need more than 2 litres, you'll find the wait time increases.
In my house, the time to get reasonably hot water for a shower was about 13 seconds. With the NR-240A, it was about 24 seconds. This is not a scientific experiment, but a subjective one. But let's face it, the finger test is what most of us use before we get into the shower, so it's probably quite accurate.
One thing about the above information are worth noting:
1) You'll waste a bit more water waiting for your shower to get warm enough with this tankless heater
It's also worth noting that if you turn on a small hot water draw - like the sink hot water tap, and let it run while you look for your shower cap, that the hot water will start to flow with a small water draw - and be ready for your shower - without taking a lot of extra water.