The biggest difference that we see from the plumber’s perspective is the engineering and overall simplifications. These tankless heaters are practically jet engines, and when installed properly and regularly maintained, will last 20+ years. Navien backs their products with the longest warranty within the industry… 15 years on the heat exchanger and 5 years on all other parts. This is as long as the installation is done correctly, and that the tankless unit’s regularly scheduled maintenance is completed and can be verified. As of this writing (2024), Navien is the only tankless water heater that uses stainless steel for its main components and heat exchanger versus copper. Copper is suitable, but stainless steel is far superior in strength and corrosion resistance. Especially when considering the combustion temperatures and the molecular changes that take place in that process.