A tankless water heater such as a Rinnai model isn't worth the investment for at least two decades, as stated by Consumer Reports. Gas tankless heaters proved themselves about 22-percent more energy efficient, which translates into savings of around $70 to $80 per year, as of 2015.
A conventional tankless water heater costs from about $800 to $1,150, while the more economical storage-tank heaters cost from $300 to $480. This big gap between prices means that it can take up to 22 years to break even on the investment of a tankless water heater. Tankless water heaters also need more maintenance and have a life span of about 20 years, which makes the investment unreliable.