An installer needs to provide heat from a conventional gas-fired boiler to a large buffer tank. The tank is necessary because of a highly zoned distribution system.
When helping homeowners choose between tank-type and tankless water heaters for a specific application, it’s advisable to get an impartial recommendation from a manufacturer that offers both technologies.
In 1970, when I started in the heating industry, there was a battle going on between the folks who believed in catching and controlling the air in a hydronic system by holding it inside a plain-steel compression tank, and those who thought it was best to catch the air and just get rid of it using automatic air vents and diaphragm-type compression tanks.
There will always be fringe markets for products that use renewable energy to provide marginal heating comfort. These markets survive because early adopters willingly sacrifice superior comfort as the perceived price for using renewable energy.