Some dealers may sell a tankless water heater to anyone who inquires about
one. That can be problematic for the customer. Some people are not good
candidates for tankless water heaters. My approach (and the one specified by
most manufacturers) is to determine the customer’s hot water demand. An elderly
couple or a single person who uses the shower once a day with a couple of small
loads of laundry once a week is not liable to realize much savings from a
tankless water heater. It would take an inordinate amount of time to gain a pay
back. By contrast, a large family, one with teenagers or small children, would
have a moderate to severe hot water demand, realizing a pay back in a much
shorter span of time. They are the ones who would benefit the most from a
properly sized tankless water heater installation.
Ask the dealer to see the factory sizing chart that specifies temperature
rise and flow rates. Ask them to explain the numbers and make sure the unit you
are considering is sized to provide the quantity of hot water you want at the
desired temperature. Paying a lot of money for a unit that underperforms is
unsatisfactory at best.
Finally, as with any large purchase, shop around. You may find quite a price
difference between installers. Enjoy your new tankless water heater and the
many benefits it can afford, knowing you are contributing to energy
conservation and a better environment.