Tankless hot water heaters are an on-immediate hot water system source that can be very efficient to use. The standard water heater today is a 40 to 50 gallon constant heater is in use predominately.
If you turn the furnace or heater off in your house when you away from it why would you keep wasting energy with a water heater that is kept at a constant temperature on idle while you are gone. Unlike traditional storage heaters the tankless just heats as is the tankless system cold water entering the pipe at the entry to a tankless system is heated immediately when you call for it by turning on your tap in either the kitchen or the bathroom. If your unit is gas fired, a gas burner heats the water. If it is electric, an electric element heats the water.
This produces a constant source of hot water as needed at about 2 to 5 gallons per minute A gas fired tankless unit will produce a higher flow rate than one powered by electricity. However the immediate demand system is not the universal choice for heating is due to an inability to produce the immediate hot water for a large family at the same time with baths and showers and kitchen cleanup being done.Simultaneous use of different water services quickly reaches a limit where it cannot deliver.
Perhaps your local plumber did not explain all of the alternatives and facts to you when your system was installed. You could have the option of running two tankless devices in parallel at the same time this increasing the output capacity at peak draw other opportunity that your favoured plumber could recommend is to run the bathrooms and dishwashers on one circuit and the laundry room services on a different circuit using the two tankless latter provides that there is hot water for everyone when they want it.
Talk to your licensed and insured plumber and see what alternative or mix they would suggest to you for your satisfaction. Once you have the tankless water system your contribution to the green movement and rapid hot water will warm your head and your heart.