fourth year
They need a lot of electricity or gas to heat the water as it goes through the system. A gs unit will need a much larger chimney flue due to the larger burner. Unless it has a flow regulator to limit the water velocity through the heater, the outlet temperature will drop was the flow increases beyond the optimum for the burner input. Scale buildup in the heater will reduce its efficiency tremendously. And when you need parts or repairs, there is a good chance the company will be out of business and the parts, being specific to that heater, will no longer be available. And you will not save a lot of energy, since you will still have to run the cooled water out of the pipes before you get hot water at the faucets, just like a tank type. The only justification for a tankless heater is if you do not have space for a conventional one, or you are going to install multiple units and locate them at the various bathroom units to eliminate the water wasting while waiting for the hot water to arrive.
